Scholarly article on [(17beta)-3-oxoandrost-4-en-17-yl]methyl acetate 4975-51-3 from Helvetica Chimica Acta p. 1262,1265

BEHAVIORAL AND BRAIN SCIENCES (2000) 23, 573–644

Printed in the United States of America

The evolution of human mating:

Trade-offs and strategic pluralism

Steven W. Gangestad

Department of Psychology, University of New Mexico, Albuquerque, NM

87131

sgangest@unm.edu

Jeffry A. Simpson

Department of Psychology, Texas A&M University, College Station, TX 77843

jas@psyc.tamu.edu.

Abstract: During human evolutionary history, there were “trade-offs” between expending time and energy on child-rearing and mating,

so both men and women evolved conditional mating strategies guided by cues signaling the circumstances. Many short-term matings

might be successful for some men; others might try to find and keep a single mate, investing their effort in rearing her offspring. Recent

evidence suggests that men with features signaling genetic benefits to offspring should be preferred by women as short-term mates, but

there are trade-offs between a mate’s genetic fitness and his willingness to help in child-rearing. It is these circumstances and the cues

that signal them that underlie the variation in short- and long-term mating strategies between and within the sexes.

Keywords: conditional strategies; evolutionary psychology; fluctuating asymmetry; mating; reproductive strategies; sexual selection

Research on interpersonal relationships, especially roman-

tic ones, has increased markedly in the last three decades

attributes (e.g., physical attractiveness) tend to assume

greater importance in mating relationships than in other

types of relationships (Buss 1989; Gangestad & Buss 1993

[see also Kenrick & Keefe: “Age Preferences in Mates Re-

flect Sex Differences in Human Reproductive Strategies”

BBS 15(1) 1992]). Specific facial and body features predict

the attractiveness of mates in nearly all cultures (Cunning-

ham et al. 1990; Jones & Hill 1993; Perrett et al. 1994).

Marriage is culturally universal (Daly & Wilson 1988). This

(

see Berscheid & Reis 1998) across a variety of fields, in-

cluding social psychology, anthropology, ethology, sociol-

ogy, developmental psychology, and personology (Ber-

scheid 1994). Unfortunately, these diverse perspectives

have not coalesced into larger, more integrative theories of

how and why relationships function the way they do.

Evolutionary principles can integrate the findings on in-

terpersonal relationships, especially concerning mating and

parental behavior. In the evolutionary approach one tries to

understand human psychological design – the nature, or-

ganization, and operation of domain-specific psychological

mechanisms – by identifying plausible constraints from

selection pressures during evolutionary history (see Buss

Steven W. Gangestad is Professor of Psychology and

Regents’ Lecturer at the University of New Mexico. He

received his Ph.D. from the University of Minnesota in

1

995). Human behavior is highly flexible and environmen-

tally responsive but “[psychological] designs that produce

plasticity’ can be retained by selection only if they have fea-

1

986. In the past decade, his major research interests

have been in evolutionary psychology, with particular

emphasis on human sexual selection, the evolution of

mating strategies, the maintenance of genetic variation

in populations, and the evolutionary-genetic underpin-

nings of neurodevelopmental variation.

‘

tures that guide behavior into the infinitesimally small re-

gions of relatively successful performance with sufficient

frequency” (Tooby & Cosmides 1992, p. 101). To under-

stand behavioral flexibility (i.e., the ability to adjust adap-

tively to specific environmental circumstances), especially

in the form of cultural variation, one must understand the

psychological architecture that guides social interactions.

Romantic relationships have several unique qualities

that distinguish them from other types of relationships.

Romantic love, for example, differs from other forms of

love (Hendrick & Hendrick 1986). Sexual jealousy has fea-

tures and consequences that differ from other types of jeal-

ousy (Daly & Wilson 1988; Daly et al. 1983). Specialized

verbal and nonverbal courtship rituals are observed in vir-

tually all cultures (Eibl-Eibesfeldt 1989). Certain personal

Jeffry A. Simpson, Professor of Psychology at Texas

A&M University, received his Ph.D. from the Univer-

sity of Minnesota in 1986. He has written over 70 pub-

lications in social/personality psychology. Most of his

research focuses on interpersonal relationships, partic-

ularly mating, attachment, and relationship mainte-

nance processes. He has served on the Social Psychol-

ogy grant panel at the National Science Foundation,

serves on the editorial boards of several journals, and

currently is the editor of the journal Personal Relation-

ships.

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573

Gangestad & Simpson: Evolution and human mating

all suggests that a specialized psychological architecture

may underlie and guide romantic interactions. This would

make sense considering the importance of mating, repro-

duction, and parenting throughout evolutionary history.

The fact that the ties between mating and reproduction

can now be severed by contraception does not imply that

evolved psychological mechanisms no longer influence hu-

man mating (see Symons 1987; 1992; Thornhill 1991;

Tooby & Cosmides 1992). [See also BBS multiple book re-

view of Symons’s The Evolution of Human Sexuality, BBS

1. Basic evolutionary concepts

1.1. Sexual selection

Sexual selection refers to discrepancies in reproduction

rates among individuals resulting from the various “advan-

tages” in mating, independent of advantages resulting from

differential survival. Evolutionary biologists have tradition-

ally studied the effects of sexual selection on two kinds of

adaptations: (a) intrasexual competitive abilities, and (b)

specialized signals that appeal to members of the opposite

sex (Andersson 1994). In many species, the number of dif-

ferent mates that one sex can obtain is related directly and

strongly to reproductive success, whereas this is less true of

the other sex. In most mammals, the former sex is male, and

the latter, female (whose reproductive output is limited by

internal gestation and lactation). Thus, in most mammals,

females are a limited reproductive resource for males, who

compete to attract mates. Given this disparity, sexual selec-

tion pressures should have acted more strongly on the male

intrasexual competitive abilities and the specialized signals

appealing to female preferences than vice versa (see Cronin

2

, 1980.]

Evolutionary theories of human mating have been heav-

ily influenced by research on mating in other animals (see

Campbell et al. 1999). These theories – especially Trivers’s

(

1972) theory of sexual selection and parental investment –

clarified the major (and slightly different) barriers that

males and females in most species must surmount to in-

crease their inclusive fitness. Trivers’s work launched the

strong theoretical and empirical focus on sex differences in

human mating strategies, most of which has tried to explain

why women, in comparison with men, tend to be more dis-

criminating when choosing mates and more “restricted” in

their sexual behavior. Recently, Buss and Schmitt (1993)

have applied and extended many of Trivers’s ideas in devel-

oping their Sexual Strategies Theory (SST). The focus on

sex differences in human mating has been criticized, how-

ever, for not explaining why there is more variation in mat-

ing-related behaviors within sexes than between (see

Gangestad & Simpson 1990) and for not considering how

women’s control of resources may have influenced the mat-

ing strategies of both sexes (see Gowaty 1992a; 1992b; Hrdy

1

991; Trivers 1972). Empirical evidence supports these

predictions in many different species (see Trivers 1985).

Theories about the signals or cues that females prefer in

mates have focused on two types: (a) attributes that tend to

signal qualities of a “good parent” (or a “good provider”),

and (b) attributes suggesting that an individual may have

“

good genes” (Cronin 1991; Gangestad 1993; Miller 1998).

Theories of good parenting have been fairly uncontrover-

sial. Those involving good genes, on the other hand, have

been debated extensively (see sect. 3). Consequently, most

applications of sexual selection to human mating have not

seriously considered good-gene sexual selection. Recently,

however, theoretical and empirical research has indicated

that both good-parenting and good-gene selection could

have operated on many species (Kirkpatrick 1996; Møller

1

997).

In this target article, we show how evolutionary princi-

ples can extend and deepen our understanding of human

mating, and how and why both sexes display both short- and

long-term mating tactics in certain contexts. SST (Buss &

Schmitt 1993) tries to explain why men tend to adopt short-

term mating tactics more often than women. SST also em-

phasizes that both men and women have evolved mixed

strategies involving both long- and short-term matings. Af-

ter reviewing SST, we will argue that selection produced

mixed strategies that depend on environmental circum-

stances and their cues. Men and women accordingly shift

between short- and long-term mating, with considerable

variation within each sex.

The target article has six major sections. In the first, we

discuss basic concepts in evolutionary biology that are rel-

evant to mating, paying particular attention to trade-offs

and their adaptive role. In section 2, we summarize previ-

ous theoretical claims about sex differences in short-term

mating in humans, including Sexual Strategies Theory. We

discuss how existing theories fail to incorporate trade-offs

to explain fully within-sex variation in mating tactics. In sec-

tion 3, we discuss how and why genetic fitness and models

of good-gene sexual selection should affect mating deci-

sions and behavior. In the fourth section, we review recent

evidence concerning good-gene sexual selection in hu-

mans. In section 5, we discuss how good-gene and good-

provider sexual selection should affect how men and

women make trade-offs and hence why individuals engage

in different mating tactics. We also discuss how different

environmental factors should affect the expression of short-

and long-term mating tactics within each sex. Section 6 is a

short summary of the target article.

1

994b), particularly those in which males provide substan-

tial parental care (as is true of humans). In what follows, we

will argue that these selectional processes are likely to have

produced differential mating tactics within each sex.

Natural selection also has important implications for hu-

man mating. In many species, parental care by males might

have evolved to increase offspring fitness directly and, thus,

could have evolutionary benefits (Clutton-Brock 1991), par-

ticularly in humans (Lancaster & Lancaster 1985). Natural

selection could also have led females to obtain the resources

necessary to reproduce and compete for additional re-

sources (Gowaty 1992a; Hrdy 1981). Moreover, mating can

have benefits that are indirectly derived from reproduction

and are not associated with sexual selection. For example,

females may induce paternity uncertainty by having multi-

ple mates, possibly leading to more protection or greater tol-

erance of offspring by different men (Hrdy 1981).

1.2. Adaptations

Adaptations are traits that gave individuals a gene-transmit-

ting advantage over other individuals who had different vari-

ants of the traits found in the original environments in which

the traits evolved (i.e., in the “environment of evolutionary

adaptedness” or EEA; Alcock 1993). They are identified by

showing that specific traits or behaviors meet the require-

ments of “special design” (Williams 1966), evidence that a

trait shows specificity, efficiency, and economy for produc-

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Gangestad & Simpson: Evolution and human mating

ing a particular beneficial effect (the “function” of the trait).

In many instances, adaptive behavioral flexibility should be

facilitated by domain-specific psychological mechanisms

tempting to attract additional mates). Thus, costs include

the lost benefits of potentially productive yet foregone ac-

tivities (Gross & Sargent 1985).

(Tooby & Cosmides 1992). These mechanisms should oper-

If fitness gains arising from mating effort (through in-

creased access to more mates) are greater for one sex, se-

lection should tilt the balance toward more mating than

parental effort in that sex compared to the other (see Low

1978). Because obtaining more mates (a component of mat-

ing effort) cannot produce large fitness gains for females in

many species (e.g., Bateman 1948), the average females in

those species should devote more time and energy to

ate according to specific decision rules that are activated by

certain environmental cues and that produce efficient, sta-

ble, persistent, and finely tuned responses (e.g., specific per-

ceptions, arousal, behavioral reactions) designed to solve

specific adaptive problems (e.g., choosing or attracting

mates). These decision rules do not have to be consciously

formulated or under deliberate control. During puberty, for

example, individuals’ physiological adaptations “decide” to

produce secondary sexual characteristics. Likewise, the ba-

sis of attraction to a potential mate, suspicions about a mate’s

infidelity, or interpretations of flirtatious glances are all re-

sponses to specific environmental cues that are likely to be

2

parental investment than the average male. Conversely,

most males in these species should devote a greater portion

of their time, energy, and effort to finding and attracting

mates than most females. Hence, trade-offs are implicit in

the prediction that males and females should, on average,

differ in the total reproductive effort they devote to mating,

a prediction that is central to many theories of human mat-

ing. These same notions about trade-offs also lead to the ex-

pectation that males should differ from one another in the

total amount of reproductive effort devoted to mating.

As an illustration, consider Burley’s (1986) innovative

research on zebra finches. She found that when females

mated with males who were experimentally manipulated to

be more “attractive,” females increased their parental in-

vestment in the resultant offspring. As a result, males actu-

ally decreased the amount of parental effort they exerted

and, at the same time, experienced greater success in extra-

pair matings. Thus, when a male’s mating effort was more

productive, he exerted more mating effort at the expense of

reduced parental effort. This notion has not been fully in-

corporated into existing theories of human mating.

1

governed by implicit, unconscious decision rules.

1.3. Evolutionary functional analysis and trade-offs

Evolutionary theory existed for more than a century before

Williams’s (1966) groundbreaking work on adaptations.

This lag occurred because “classical Darwinists” viewed

adaptations almost exclusively in terms of the benefits they

bestowed on organisms; associated costs were not fully con-

sidered (Cronin 1991). Individuals must invest consider-

able time, effort, and energy to accomplish the major tasks

that most directly affect their inclusive fitness: surviving to

reproductive age, reproducing successfully, and rearing off-

spring to reproductive age. These factors are important not

only because they put individuals at risk (and, hence, can

decrease their future reproductive success, despite imme-

diate benefits), but because individuals could have used

these resources differently. Thus, adaptations have “oppor-

tunity costs” associated with them – costs that accrue from

lost fitness benefits that might have been achieved by using

resources in different ways. A major “modern Darwinian”

insight was that one must weigh the benefits in relation to

the costs to appreciate whether and how adaptations

evolved during evolutionary history (using cost-benefit

analyses: Parker & Maynard Smith 1991). The funda-

mental goal of evolutionary analysis is to specify the cost-

benefit “trade-offs” that led individuals to allocate their

time, energy, and effort to activities in ways that increased

their ancestors’ inclusive fitness.

2. Existing theories of sexual strategies

2.1. The concept of sexual strategies

Sexual strategies (or mating strategies) are integrated sets

of adaptations that organize and guide an individual’s re-

productive effort. They influence how individuals select

mates, how much mating effort they expend, how much

parental effort they expend, and so on. As discussed in sec-

tion 1.2, sexual strategies are not necessarily formulated

3

consciously or even accessible to awareness. Strategies

typically are defined as genetically based programs (i.e., de-

cision rules) that individuals use to allocate their somatic

and reproductive effort to specific alternative phenotypes

(i.e., mating tactics) in adaptive ways. Tactics in turn are the

specific actions and behaviors in which individuals engage

when pursuing a given strategy. A mating strategy often in-

volves multiple behavioral tactics (Dominey 1984).

1.3.1. Parenting effort versus mating effort. Trade-offs are

illustrated by the differential allocation of effort to parent-

ing versus mating activities. Trivers (1972) defined parental

investment as “any investment by the parent in an individ-

ual offspring that increases the offspring’s chance of surviv-

ing (and hence reproductive success) at the cost of the par-

ent’s ability to invest in other [including future] offspring”

Consider, for example, Trivers’s (1972) hypothesis that

males in many biparental investing species may invest heav-

ily in offspring, yet remain open to low-cost mating oppor-

tunities with other females. This is a mixed mating strategy

involving multiple behavioral tactics in which each tactic is

displayed with a certain frequency. If each tactic is cued by

specific environmental stimuli (e.g., the prolonged absence

of a mate, having short-term sex only with mates who have

certain attributes, seeking short-term sex only when such

efforts have paid off in the past), the strategy is conditional.

(

p. 139, emphasis ours). This definition implies a basic

trade-off. Parental investment can increase the probability

that offspring will survive and subsequently reproduce,

yielding greater fitness. However, parental investment also

has costs. Indeed, according to Trivers (1972), the amount

of investment is measured in units of lost benefits of alter-

native investment (i.e., lost opportunities to invest in other

offspring). Individuals who engage in parental effort (the

sum total of parental investment in all offspring; Low 1978)

could be doing other things with their limited time and en-

ergy, such as devoting greater effort to mating (e.g., at-

2.1.1. Conditional strategies. In the last two decades, evo-

lutionary theorists have begun to acknowledge that selec-

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Gangestad & Simpson: Evolution and human mating

tion pressures should not have produced a single “best”

mating tactic (or mixture of tactics) for males and females

in most species. Instead, selection should have fashioned

considerable phenotypic diversity in mating (Gross 1996).

Guided by concepts from game theory (Maynard Smith

another and most intensely during breeding season. In most

species, assertiveness is the most profitable male strategy. Dur-

ing the full period of time it takes to bring a fetus to term, from

the fertilization of the egg to the birth of the infant, one male

can fertilize many females but a female can be fertilized by only

one male. Thus if males are able to court one female after an-

other, some will be big winners and others will be absolute

losers, while virtually all healthy females will succeed in being

fertilized. It pays males to be aggressive, hasty, fickle, and

undiscriminating. In theory it is more profitable for females to

be coy, to hold back until they can identify males with the best

genes. In species that rear young, it is also important for the fe-

males to select males who are more likely to stay with them af-

ter insemination. . . . Human beings obey this biological prin-

ciple faithfully. [p. 129; emphasis ours]

1

982 [see also Maynard Smith “Game Theory and the Evo-

lution of Behaviour” BBS 7(1) 1984]) and the theory of evo-

lutionarily stable strategies (Dawkins 1980; Parker 1984),

evolutionary biologists are now documenting how having

alternative mating tactics gives individuals of each sex dif-

ferential reproductive fitness in various species. Although

relatively little theory and research have focused on the

mating behavior of human beings, hundreds of studies have

confirmed that males and females in a wide range of species

display alternative mating tactics that reflect conditional

strategies (Gross 1996). Burley’s (1986) finding that male

zebra finches’ relative allocation of parental effort and extra-

pair mating effort is contingent on their attractiveness is a

good illustration of a conditional strategy.

Conditional strategies have five main properties (see

Gross 1996): (a) They involve different behavioral tactics

that are consciously or unconsciously “chosen” by an indi-

vidual; (b) the choices between tactics are “made” in re-

sponse to specific features or cues in the environment, of-

ten an individual’s status or attractiveness relative to other

individuals; (c) all individuals are genetically monomorphic

More recent theories of sex differences in mating have

incorporated similar notions. Perhaps the most ambitious

of these new theories is Buss and Schmitt’s (1993) Sexual

Strategies Theory (see also Buss 1994b; 1998a; 1998b).

Buss and Schmitt’s theory emphasizes that both men and

women should have evolved tactics for obtaining long-term

mates and investing in offspring. Similar to Wilson’s (1978)

theory, however, SST predicts that men should have

evolved to seek multiple mates in particular:

What specific adaptations should be expected in the evolved

sexual psychology of men to solve the problem of gaining sex-

ual access to a number of women? One first-line solution to the

problem of number can be expected in desire: Men may have

evolved over human evolutionary history a powerful desire for

sexual access to a large number of women (cf. Symons, 1979).

(

i.e., they are are genetically designed to enact the same tac-

tics); (d) during their evolution, the average adaptive values

of different tactics were not equal except at a “switchpoint”

on a continuum of environmental input (e.g., individuals’

relative status) where the costs and benefits of each tactic

balanced out; and (e) during their evolution, the chosen tac-

tic tended to yield higher fitness for the individual than

other tactics given current environmental conditions. Thus,

the environmental conditions moderate the fitness gains of

pursuing different tactics (e.g., exerting parental effort,

pursuing short-term matings), thereby affecting the opti-

mal allocation of effort to different tactics.

(

Buss & Schmitt 1993, p. 208; emphasis ours.)

This prediction is based on an implicit cost-benefit analy-

sis that involves trade-offs between different activities that

were presumably optimal for men and women in evolu-

tionary history. According to SST, men experienced, on av-

erage, a greater net benefit than women from attempting to

attract multiple mates. This prediction has received empir-

ical support in several recent studies. For example, men re-

port desiring four times as many sex partners in the next five

years as women do (Buss & Schmitt 1993).

If males differ in the conditions under which they engage

in different tactics, they are enacting alternate conditional

strategies. Although alternate strategies can be noncontin-

uously distributed in a population (e.g., if certain males

never invest in offspring and always seek short-term mates),

they are usually distributed continuously. This should occur

if males differ in how long they tolerate their mate’s absence

before pursuing other mates, or if males differ in the degree

to which they expect extra-pair mates to have certain desir-

able attributes (Dominey 1984). Alternate strategies can re-

flect genetic polymorphisms (see Gross 1996). Although

such polymorphisms exist in nature and may underlie cer-

tain variations in human mating strategies (see Gangestad

2

.3. A sex-specific universal?

Evidence indicates that men do, on average, desire and

seek short-term mates more than women do. Wilson

(1978), however, makes an even stronger prediction about

this sex difference. He claims that males should benefit by

being “aggressive, hasty, fickle, and undiscriminating.” This

should hold true for all males in a species. Although Buss

and Schmitt (1993) do not explicitly claim that all men have

a “powerful desire for sexual access to a large number of

women,” they do not qualify their statement to indicate that

some men may not. Clearly, a mean sex difference – even

a large one – does not imply a near-universal propensity in

each sex. Indeed, a mean sex difference could exist even

when the modal response of each sex is similar (e.g., when

the distribution for one sex is more variable and skewed

than for the other sex).

Sex differences in the desire for multiple sex partners and

interest in engaging in short-term mating are moderate in

magnitude. Buss and Schmitt (1993) report ␥s (i.e., the

number of within-sex standard deviations on which the

means of the two sexes differ) for each effect they found.

We converted this statistic to percentages of variance ac-

counted for on each variable by sex. Sex accounts for 16%

&

Simpson 1990; Wilson 1994), we focus on conditional

strategies in this article.

2.2. Sex differences in sexual strategies

Most evolutionary theories of mating have focused on the

different strategies purportedly adopted by men and wo-

men. Based on Trivers’s (1972) theorizing, Wilson (1978)

suggested that men and women differ along an assertive-

ness-coy dimension:

The . . . conflict of interest between the sexes is a property of

not only human beings but also the majority of animal species.

Males are characteristically aggressive, especially toward one

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Gangestad & Simpson: Evolution and human mating

of the variance in seeking short-term mates, 9% of the vari-

ance in the number of sex partners desired within a speci-

fied time, and 20% of the variance in the probability of con-

senting to sex after knowing an attractive, opposite-sex

person for a given length of time. In a recent meta-analysis,

Oliver and Hyde (1996) found that the mean sex difference

in interest in casual sex accounted for 25% of the variance.

Across different college samples, we have found that sex ac-

counts for 8%–20% of the variance in expressed interest

and willingness to engage in sex without commitment

view of Kitcher’s Vaulting Ambition: Sociobiology and the

Quest for Human Nature, BBS 10(1) 1987]; Maynard Smith

1982). Similarly, the best strategy for women may not al-

ways be to devote less effort to pursuing short-term mates

than the average male.

From our perspective, the basic notion that men, on av-

erage, evolved to engage in greater mating effort than

women correctly assumes that some ancestral males could

have increased their fitness by trying to attract multiple

mates. However, the more stringent notion that the best

evolutionary strategy for most men should have been to

pursue multiple mates assumes that most men were suc-

cessful at short-term mating. This is a dubious assumption.

Men’s short-term mating success should have depended

partly on which attributes women preferred and desired in

short-term mates. Relatively few men are likely to have sat-

isfied these preferences. Thus, for some men, one cost of

engaging in short-term mating would have been the loss of

opportunities to engage in parental investment (which hu-

man males also evolved to do: see Alexander & Noonan

1979; Lancaster & Lancaster 1985). If short-term mating

effort generated poor payoffs for men who did not have the

attributes most women desired in short-term mates, these

costs should have outweighed the benefits of pursuing

short-term mating. Hence, the most profitable mating

strategy for the typical man may have been to devote most

of his reproductive effort to enhancing the phenotypic qual-

ity of his offspring by investing heavily in a single mate’s off-

spring, despite the fact that a few men with certain desir-

able attributes were even more successful when they

adopted short-term tactics.

(

Simpson & Gangestad 1991a).

Although these effect sizes are fairly large by conven-

tional standards (Cohen 1977), substantial amounts of

within-sex variation and overlap exist between the distribu-

tions of women and men. For example, despite the mean

sex difference in the desire to have sex without commit-

ment (Simpson & Gangestad 1991a), approximately 30% of

men express less favorable attitudes about casual sex com-

pared to the median attitudes of women. Substantial over-

lap also exists for many other measures, including interest

in sex with multiple partners and optimal time before hav-

ing sex (see Miller & Fishkin 1997). Generic claims that

women desire certain mating arrangements whereas men

desire others raise the questions “which men?” and “which

women?” (Gowaty 1992b). If the within-sex variation in

mating strategies is adaptive, the environmental contingen-

cies in the EEA that led men and women to adopt short-

term versus long-term mating tactics must be specified.

Sexual Strategies Theory acknowledges that both sexes

can and do exhibit short-term and long-term mating tactics

(

i.e., that human mating strategies are mixed); indeed, this

is one of SST’s defining features. Buss and Schmitt (1993)

also explicitly note that within-sex variation in mating tac-

tics may be adaptive. Nonetheless, within-sex variation has

received less theoretical attention than sex differences have

and it remains an “unresolved issue” (Buss & Schmitt 1993)

within SST (see also Buss 1998a). Moreover, to state that

Consider a parallel example where the currency of profit

is money rather than fitness. Suppose that brain surgeons

make more money than everyone else does. Clearly, it is not

the “most profitable” money-making strategy for everyone

to decide to become a brain surgeon. Only so many people

can become brain surgeons; hence, most people would be

bound to fail. Instead, the most profitable strategy for most

people would be to select careers that provide them with

the most money, given their abilities and, in competitive

markets, their chances of success.

“

[m]en who lack mechanisms such as a desire for a variety

of partners . . . would have been out-reproduced by men

who successfully solved [the problem of partner number]

entailed by the pursuit of a short-term mating strategy”

(

Buss 1998a, p. 24) is to imply that evolution would not have

If the most evolutionarily profitable strategy for men de-

pended in part on the attributes each man possessed (e.g.,

his ability to attract multiple, short-term mates), what sex-

ual strategy should have evolved in men? The answer is a

conditional mating strategy (see Gross 1996; Trivers 1972).

Most men would probably have profited from substantial

investment in a primary mateship (or small set of mate-

ships), investing fairly heavily in subsequent offspring.

When men could obtain short-term, opportunistic matings

with other women (often other men’s primary mates), they

could have profited by pursuing the sex-typical strategy out-

lined by Wilson (1978) and Buss and Schmitt (1993). How-

ever, when they could not, men should have shifted greater

amounts of time, energy, and other resources to long-term

mating (including mate guarding) and parental investment

to attract and retain one mate and derive the benefits of

parental investment. Although men may have “evolved over

evolutionary history [the capacity for] a powerful desire for

sexual access to a large number of women” (Buss & Schmitt

1993, p. 208; our addition and emphasis), the desire for

short-term mating should be expressed conditionally, and it

should be observed infrequently under conditions when

only a few men are able to attract short-term mates. The key

favored a male strategy entailing little desire for multiple

mates. However, as we shall see, most men may have ben-

efited reproductively by having little interest in pursuing

multiple mates. Both the desire for multiple mates and the

lack of this desire should have been beneficial under cer-

tain conditions.

2.4. Cost-benefit considerations

If aggressiveness and interest in short-term mating is the

most profitable” strategy for men, why do only some men

“

pursue short-term mates? Differential cost-benefit trade-

offs should have led men to pursue more mates on average

than women. Consequently, men should, on average, dedi-

cate more time and energy to mating effort than women.

These premises, however, do not lead to the conclusion that

the best strategy for most males would involve high mating

effort, whereas the best strategy for most females would en-

tail high parental effort. A consideration of trade-offs sug-

gests that the best strategy for men may not always – or

even usually – be to devote effort to pursuing short-term

mates (see Kitcher 1985 [see also BBS multiple book re-

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Gangestad & Simpson: Evolution and human mating

adaptation should be a set of decision rules about when and

how to allocate reproductive effort wisely and contingently,

rather than a universal desire for short-term mating. As

noted above, this is not a novel notion. Conditional strate-

gies are a central topic in behavioral ecology (see Krebs &

Davies 1993, on “making the best of a bad job”; see also

Dawkins 1980; Gross 1996). However, the possible role of

conditional strategies in human mating has received rela-

tively little attention (see Buss 1998a; Buss & Schmitt

typically greater than those of ordinary morphological traits

(e.g., height). Human fecundity, for example, has a CV of

a

15 to 20 (Burt 1995), 4 to 5 times greater than that of human

height. Values exceeding 10 have been estimated for fitness

traits in other organisms (Burt 1995; Houle 1992), com-

pared to values around 5 for ordinary traits or traits under

stabilizing selection (Houle 1992; Pomiankowski & Møller

1995). Fitness itself has been estimated to have a CV of be-

a

tween 10 and 30 in natural populations of many species

1

993). We accordingly propose that evolution generated

(Burt 1995).

conditional strategies in both sexes, resulting in a plurality

of mating tactics.

New theoretical developments are based on the notion

that the amount of genetic variance in fitness within a

population is the result of two opposing forces: natural se-

lection (which removes genetic variation) and forces that

degrade an organism’s fitness, such as mutations and envi-

ronmental change (both of which enhance genetic varia-

tion: Fisher 1958). As long as deleterious mutations and en-

vironmental change are negligible, natural selection should

keep genetic variance near zero. Recently, population ge-

neticists have begun to model and estimate the amount of

genetic variance in fitness that can be maintained by muta-

tions alone. The genome-wide mutation rate (i.e., the num-

ber of new deleterious mutations per organism) is about

1 in Drosophila, a rate that explains at least half of its esti-

Trivers (1972) also noted that “the optimal [mixed strat-

egy] is likely to differ for different males” (p. 146). Trivers

was in fact the first evolutionary theorist to acknowledge

that selection could have favored adaptations that led some

males to devote very little time and effort to short-term

mating. It is ironic that his classic article is often cited as

suggesting that the most profitable strategy for males

should be to pursue short-term mating almost universally.

What attributes have women evolved to desire in short-

term mates? It is important to identify these attributes be-

cause they should moderate strategy choice in men. In the

next section, we suggest that good-gene sexual selection

may be central to answering this question. As we shall see,

these selection pressures may also have important implica-

tions for understanding variation in women’s interest in

short-term mating.

mated genetic variance in fitness (a CV of 6–17; Charles-

a

worth 1990; Charlesworth & Hughes 1998). The genome-

wide mutation rate in humans is probably higher, given our

larger genome (Charlesworth 1990). Thus, mutations prob-

ably account for a human CV f fitness of 10 or more.

ao

Hence, mutations alone might produce more genetic vari-

ance in fitness than is observed in most ordinary traits.

Recent theory has also drawn attention to phenomena

that induce rapid change in the selective environments of

organisms. Pathogens are one set of the strong selective

forces operating on long-lived organisms such as humans.

Because parasites evolve in response to their hosts’ de-

fenses against them, no set of host defenses is evolutionar-

ily stable; these defenses are always being challenged by

changing parasites. These rapid shifts in the selective envi-

ronments of hosts ensure not only that hosts will never

be free of maladaptations caused by parasites, but that they

will vary in their ability to resist parasites. Hence, host-

parasite coevolution maintains genetic variance in host fit-

ness (Anderson & May 1982; Haldane 1949; Hamilton

3

. Genetic fitness and sexual selection

In many species, males provide little or no parental invest-

ment. Yet even in these species, females are selective and

consistently prefer certain males over others as mates.

Good-gene sexual selection (GGSS) can explain female

mate preferences in species that do not have much pater-

nal investment (Cronin 1991). According to models of

“

good gene” selection, females have evolved to prefer males

who possess indicators of viability and good condition, that

is, adaptive attributes that might be passed on to their off-

spring through genetic inheritance.

3.1. Genetic variation in fitness

1

982; Tooby 1982).

For mate preferences based on indicators of heritable fitness

to evolve, additive genetic variance must underlie fitness

It is important to emphasize that alleles that are good

genes at one point in time need not be intrinsically better

than alternative alleles. Host-parasite coevolution imposes

changing selection pressures on host genes, maintaining

heritable fitness in individuals. Thus, an allele that is a good

gene today might be selected against in future generations,

and an allele that is currently selected against could become

a “good gene” in the future. Because no gene is inherently

better than an alternative one, the population does not be-

come more fit through selection.

(

i.e., fitness must be transmitted genetically across genera-

tions). Historically, GGSS has been controversial because

population geneticists have assumed that selection typically

reduces the heritability of fitness to nearly zero (e.g., see

Kirkpatrick’s [1985; 1986] arguments against the “sexy son”

[Weatherhead & Robertson 1979]). Recent empirical and

theoretical developments, however, have led even the harsh-

est critic to acknowledge that GGSS can and probably has

occurred in a variety of species (see Kirkpatrick 1996).

The new empirical development is the ability to estimate

the actual amount of genetic variation in fitness (or fitness

components) in natural populations. The most relevant

measure of genetic variation is the additive genetic coeffi-

In combination, mutation and host-parasite coevolution

can maintain a substantial amount of genetic variance; as

a result, fitness traits contain relatively large amounts of

genetic variance in natural populations. Moreover, recent

theoretical models indicate that large amounts of genetic

variance in fitness not only can but do produce GGSS (Kirk-

patrick 1996; see also Andersson 1986; Charlesworth 1988;

Grafen 1990; Heywood 1989; Iwasa et al. 1991; Pomi-

ankowski 1987).

cient of variation (CV ), the genetic standard deviation of a

trait, standardized by the trait mean and multiplied by 100

a

4

(

Houle 1992). Houle has argued that the CV s of fitness

a

traits (e.g., longevity, fecundity) in natural populations are

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Gangestad & Simpson: Evolution and human mating

3.2. Markers of heritable fitness

3.3. Tests of good-gene sexual selection

The degree to which individuals harbor mildly deleterious

alleles or are less pathogen-resistant must be inferred

from phenotypic markers (e.g., “advertisements”: Zahavi

To test GGSS, researchers should show that direct indica-

tors of individuals’ genetic fitness are associated with their

attractiveness as a mate (particularly as a short-term mate).

Unfortunately, perfect indicators of fitness do not exist.

Tests of good-gene selection must therefore rely on indi-

rect, fallible markers of genetic fitness. The best available

measure may be fluctuating asymmetry.

1

975). GGSS must operate through honest signaling,

which explains why only certain features tend to be valid

indicators of individuals’ underlying conditions and, po-

tentially, their genetic fitness (Grafen 1990; Zahavi 1975).

If an attribute is a marker of heritable fitness, sexual se-

lection should favor new genes that simulate the valued

feature, even in individuals who do not actually have high

fitness. Thus, “cheaters” – individuals who display the se-

lected phenotypic traits or behaviors but do not have high

fitness – may invade the population. Over time, selection

should eliminate these attributes as valid cues of heritable

fitness, and preferences for them should diminish. Under

certain conditions, however, an attribute’s link with heri-

table fitness can remain honest and stable. In particular,

an attribute can remain an “honest” advertisement when

individuals who have deleterious alleles or who are less

pathogen-resistant cannot develop or maintain the at-

tribute without incurring substantial costs. Attributes that

meet this criterion are those that conditionally “handicap”

individuals who have mutations or are less pathogen-re-

sistant.

Both mutations (Pomiankowski et al. 1991) and path-

ogens (Hamilton & Zuk 1982) divert an individual’s energy

and resources. Hence, honestly advertised traits tend to be

energetically costly because individuals who have muta-

tions or are less pathogen-resistant cannot develop such

traits without diverting valuable resources from competing

demands (e.g., sustaining their immune systems: Folstad &

Karter 1992). In peacocks and other birds with extravagant

features, costly handicaps include exaggerated sexual orna-

ments and colorful plumage (Zuk et al. 1990). In many

mammals, they include large size and increased muscula-

ture resulting in sexual dimorphism for size in polygynous

species, including primates (Alexander et al. 1979).

Fluctuating asymmetry (FA) reflects the degree to which

individuals deviate from absolute perfect symmetry on bi-

lateral features (e.g., in humans, both ears, both feet; in

other species, bilateral fins, bilateral tail feathers) for which

the signed right versus left differences have a population

mean close to zero and are nearly normally distributed

(Møller & Swaddle 1997; Van Valen 1962). Asymmetry is

believed to reflect deviations in developmental design re-

sulting from the disruptive effects of environmental or ge-

netic abnormalities encountered during the lifespan (i.e.,

developmental instability: see Lerner 1954; Palmer &

Strobeck 1986; Parsons 1990; Soule 1982; Thoday 1955;

Waddington 1957). Because these disturbances lower re-

productive fitness, pronounced asymmetry reflects mal-

adaptation (Møller & Swaddle 1997). Recent meta-analy-

ses and reviews have shown that greater asymmetry is

associated with lower fecundity, slower growth, and poorer

survival in many species (Leung & Forbes 1996; Møller

1997; Thornhill & Møller 1997; see also Clarke 1998, and a

subsequent analysis by Møller 1999). FA should be a good

marker of genetic fitness because an individual’s degree of

asymmetry should be affected primarily by (1) mutations

(that cause lower metabolic efficiency and imprecise de-

velopment), and (2) diseases (that reflect an individual’s

pathogen-resistance; Møller 1992). Consequently, FA

probably reflects both genetic and nongenetic variation in

fitness. Because sexual selection should lead females to

mate with males who have phenotypic traits that signal

greater fitness, the association between FA and mating suc-

cess has been studied in many species. A recent meta-analy-

sis of these studies reveals that, on average, more symmet-

rical individuals have greater mating success (Møller &

Thornhill 1998a).

This type of selection can be understood in terms of cost-

benefit analysis. A costly trait confers certain benefits. For

example, males who have the trait may be preferred as

mates. However, having such a trait also involves costs be-

cause the resources used to develop the trait could have

been used for other purposes. At some point, the marginal

gains of investing in the costly trait begin to diminish, and

individuals should no longer be selected to invest in the trait

beyond that point. The benefits of sexual selection can be

maintained if males with different levels of heritable fitness

maximize their benefits relative to their costs (i.e., maxi-

mize their outcomes) at different levels of the costly trait

GGSS is of course not the only form of selection that

could explain these findings. In some species, more sym-

metrical males may provide greater material benefits (e.g.,

more direct and better parental care or more physical pro-

tection of young). In addition, females may find less sym-

metrical males less attractive to avoid contracting infectious

diseases from them. However, three novel sets of findings

suggest that GGSS may have occurred in humans.

First, a recent meta-analysis indicates that, across many

species, symmetry is partly heritable (Møller & Thorn-

hill 1997). Modeling the relationship between asymmetry

and underlying developmental imprecision in these data,

Gangestad and Thornhill (1999a) have estimated that the

additive genetic coefficient of variation of developmental

imprecision is approximately 15 to 20, about the same size

as other fitness traits and much greater than ordinary mor-

phological traits (e.g., height: see Houle 1992). If part of

this genetic variance is associated with fitness, the favored

status of symmetrical males may in part reflect the opera-

(

Grafen 1990).

Trivers (1972) proposed that intrasexual competitive

abilities may have evolved to be valid cues of heritable fit-

ness. Successful intrasexual competition, such as winning

physical fights, requires developing the potentially costly

attributes used in competition (e.g., muscularity) and the

expenditure of considerable energy during competition.

Just as highly viable males should be more capable of en-

during “handicapping” traits than less viable males, they

should also be able to devote more energy to developing the

physical tools needed for successful intrasexual competi-

tion. Females may in turn may have evolved to pay atten-

tion to the outcomes of intrasexual competition to assess

male fitness (Andersson 1994).

5

tion of good-gene selection (Kirkpatrick 1996).

Second, in some species in which symmetry predicts

male mating success, more symmetrical males are favored

as extra-pair mates, even when they provide little or no ma-

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Gangestad & Simpson: Evolution and human mating

terial benefits. For example, although male and female Eu-

ropean barn swallows mate seasonally and rear offspring to-

gether, their rate of extra-pair paternity is approximately

correlation between developmental imprecision and male

partner number is approximately Ϫ.38 (Gangestad &

Thornhill 1999a). Waynforth (1998) has found a similar cor-

relation (Ϫ.23) in a sample of Mayan men in Belize and has

also documented that more symmetrical men have higher

fertility. Because women should be less inclined to convert

intrasexual competitive advantages into increased numbers

of mates (see Trivers 1972), no relation between women’s

FA and their number of lifetime sex partners was predicted,

and none has been consistently found in several studies (see

Gangestad & Thornhill 1997a).

Given that these studies are based on self-report data,

the findings could be explained by a tendency for more

symmetrical men to exaggerate their past sexual behavior.

In one study, therefore, men’s scores on narcissism (a mea-

sure that reflects self-aggrandizement tendencies: John &

Robins 1994) were partialed out. Controlling for narcissism

did not attenuate the relation between men’s FA and their

number of lifetime sex partners, partial r ϭ Ϫ.27 (Ganges-

tad & Thornhill 1997b).

3

5% (Møller 1994b). More symmetrical male barn swallows

are the main beneficiaries of extra-pair mating, yet they do

not provide material benefits that enhance the reproduc-

tive success of their female mates (see Møller 1994b).

Third, in some species, more symmetrical males also pro-

vide fewer material benefits to their primary mates. For ex-

ample, more symmetrical male barn swallows spend less

time feeding their offspring than do less symmetrical males,

and they do not compensate for their lack of time with

greater feeding efficiency. In a recent review of 18 bird

species, Møller and Thornhill (1998b) have documented an

association between extra-pair paternity and the extent to

which attractive males engage in direct parental care.

Specifically, when the rate of extra-pair paternity is high

(

and, thus, when males can benefit more from trying to at-

tract extra-pair mates), attractive males perform a smaller

proportion of offspring feedings than less attractive males.

Exerting greater extra-pair mating effort should yield larger

payoffs for more attractive males, and this is evident in the

time they fail to spend engaging in a competing activity:

providing direct parental care. We suggest that this type

of trade-off also occurs in humans. Over evolutionary his-

tory, men who had indicators of genotypic quality should

have experienced larger gains in fitness payoffs than men

who lacked these indicators. Moreover, men should have

evolved to “decide” conditionally to allocate more versus

less effort to mating or parenting, depending on the degree

to which they possess these features.

4.2. Men’s extra-pair sex and FA

Extra-pair sex (i.e., sex outside a current, ongoing relation-

ship) is one form of short-term, opportunistic mating. If

women evolved to desire men with greater heritable fitness

(independent of the investment and resources these men

provided), more symmetrical men should have more extra-

pair partners (see Benshoof & Thornhill 1979; Smith 1984).

Gangestad and Thornhill (1997b) found that men’s FA does

predict their number of extra-pair sex partners, r ϭ Ϫ.17

(reflecting a latent correlation between extra-pair partners

and developmental imprecision of about Ϫ.36; Gangestad

& Thornhill 1999a). Once potential artifacts were con-

trolled (e.g., social status, socioeconomic status [SES] in

family of origin, anticipated future salary), the correlation

between FA and extra-pair sex increased slightly. Neither

men’s social status nor their resources (as indexed by their

SES and their anticipated future salary) predicted their

frequency of extra-pair sex. Although Perusse (1993) has

found that men with higher status report having more sex

partners than men with lower status, this effect did not hold

for married men in his sample. Thus, it is unclear whether

men with higher status (e.g., wealthier men) have more

extra-pair mates than men with lower status.

4

. GGSS in humans?

New evidence indicates that GGSS might have operated on

ancestral humans. Most of this evidence indicates that FA

is systematically associated with male mating success in hu-

mans. Although FA is not the only valid marker of heritable

fitness, it currently appears to be the best marker. As we dis-

cuss below, other, more visible features (such as physicality,

social dominance, and intrasexual competition tactics) are

likely to be the proximate cues that “advertise” an individ-

ual’s genetic fitness. We focus on FA because rival models

of selection do not capture the complex relations predicted

from developmental imprecision.

4.3. Women’s extra-pair sex and FA

4

.1. FA and sexual behavior

More symmetrical men should also be preferred as

women’s extra-pair mates (i.e., mates chosen by women

who already have primary mates, regardless of whether the

man has a primary mate). Gangestad and Thornhill (1997b)

found that men’s FA predicted the number of times they

were chosen as extra-pair partners by women who were si-

multaneously involved in other, ongoing relationships, r ϭ

Ϫ.26 (reflecting a latent correlation between developmen-

tal imprecision and these partners estimated to be Ϫ.60;

Gangestad & Thornhill 1999a).

If women evolved to prefer men who exhibited indicators

of genetic fitness, more symmetrical men should have more

lifetime sexual partners (see also Perusse 1993; 1994).

Thornhill and Gangestad (1994) measured the symmetry of

men and women on seven bilateral features (foot, ankle,

hand, wrist, elbow, ear width, and ear length) using digital

body calipers. They then aggregated these measures (each

standardized by feature size) to form a global index of FA.

With the effects of age partialed out, more symmetrical

men reported more lifetime partners than less symmetrical

men, r ϭ Ϫ.32. Controlling for potential artifacts (e.g.,

height, ethnicity, marital status) strengthened this effect,

partial r ϭ Ϫ.38. These effects have also been estimated in

several other studies. The weighted correlation in a sample

of more than 500 men is Ϫ.21 (p Ͻ .0001), and the latent

4.4. FA and associated traits

What personal attributes should mediate the link between

men’s FA and their number of lifetime sex partners? One

possibility is physical attractiveness (Feingold 1990), which

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Gangestad & Simpson: Evolution and human mating

Buss and Schmitt (1993) have found is important to women

when they evaluate short-term mates and Scheib (1999) has

found is particularly important to women choosing extra-

pair mates. In fact, a man’s attractiveness in short-term mat-

ing contexts is just as important to women as a woman’s at-

tractiveness is to men when men evaluate long-term mates.

Buss and Schmitt (1993) claim that this finding is consistent

with the notion that attractiveness might have been an in-

dicator of genetic fitness in ancestral environments, but

they say little about this possibility.

If preferences for attractiveness evolved in response to

GGSS, attractiveness should be correlated with markers of

heritable fitness (such as FA). Gangestad et al. (1994) mea-

sured individuals’ FA and then had coders rate their physi-

cal attractiveness from facial photographs. After controlling

for potential artifacts (e.g., age, height), FA significantly

predicted men’s facial attractiveness, r ϭ Ϫ.33, but not

women’s, r ϭ Ϫ.17, ns. That is, more symmetrical men

were rated as more physically attractive. This sex difference

has been replicated (Thornhill & Gangestad 1994), but has

not been found consistently (Gangestad & Thornhill

Because men who have traits that facilitate intrasexual

competitive success should benefit by comparing them-

selves directly with their competitors, Simpson et al. (1999)

predicted that, when competing for a woman, more sym-

metrical men would use direct competition tactics (e.g., di-

rectly comparing themselves with, and derogating, their

competitors). After measuring their FA, Simpson et al. had

men compete with other men for a lunch date with an at-

tractive woman. Each man was asked a series of questions

over a video system by a female interviewer (actually a

videotaped experimental assistant) located in another

room. After the interview was finished, the female asked

each man to tell the “competitor” (ostensibly located in a

different room) why she should choose him instead of the

competitor. Each interaction was videotaped and coded for

specific intrasexual competition tactics. Relative to less

symmetrical men, more symmetrical men were more likely

to directly compare themselves with and belittle the com-

petitor, r ϭ .49. These results support the hypothesis that

more symmetrical men should engage in direct intrasexual

competition tactics. They also provide further evidence

about the proximate cues that may “advertise” genotypic

quality (indexed by men’s FA).

1

997a). Across several studies, the correlation between fa-

cial attractiveness and body FA is significant but rather

small (see Gangestad & Thornhill 1997a). Studies of the as-

sociation between facial symmetry and facial attractiveness

have similarly yielded mixed but positive results overall

Finally, intellectual ability may be a marker of develop-

mental precision and health. In two studies, Furlow et al.

(1997) found an association between a measure of fluid in-

telligence (Cattell’s Culture-Fair Intelligence Test) and FA,

mean r ϭ Ϫ.23 (the estimated latent correlation with de-

velopmental imprecision was Ϫ.56; Gangestad & Thornhill

1999a). The size of this effect did not differ across the sexes.

(

e.g., Grammer & Thornhill 1994; Kowner 1996; Mealey et

al. 1999; Scheib et al. 1999; see also Møller & Thornhill

998). Gangestad and Thornhill (1999a) have estimated

1

that the latent correlation between developmental impre-

cision and male facial attractiveness is about Ϫ.28.

Because facial attractiveness mediates only part of the

relation between men’s FA and their sexual history, Ganges-

tad and Thornhill (1997a; 1998a) tested three other poten-

tial mediators, namely, three sexually dimorphic traits in-

volved in intrasexual competition: (1) Body mass – Humans

show moderate sexual dimorphism, consistent with their

purported ancestral polygyny (Alexander et al. 1979); (2)

Physicality – A measure of men’s muscularity, robustness,

and vigor, as rated by both men and their romantic partners;

and (3) Social dominance – A measure based on the Cali-

fornia Adult Q-Sort. Once again, a relation was found be-

tween men’s FA and their number of lifetime partners, r ϭ

Ϫ.29 (estimated by causal modeling). In addition, all three

traits associated with intrasexual competition were pre-

dicted by men’s FA, estimated rs ϭ Ϫ.31, Ϫ.39, and Ϫ.39,

for body mass, physicality, and social dominance, respec-

tively. The indirect effects mediated through these traits ac-

counted for more than 70% of the total effect of FA on the

lifetime number of partners. As expected, women’s FA did

not predict their number of lifetime partners, and it did not

correlate with any of the 3 intrasexual competitive traits, av-

erage r ϭ Ϫ.06.

The fact that men’s FA covaries with traits that should

have facilitated intrasexual competition in ancestral envi-

ronments (i.e., physical intimidation of competitors) is con-

sistent with other research showing that more symmetrical

men engage in fights with other men more often, particu-

larly fights they initiate (Furlow et al. 1998). Besides af-

fecting the outcomes of intrasexual competition, these

traits may serve as cues that women use to evaluate men as

potential short-term mates. This would explain why all

three traits mediate the link between men’s FA and their

sexual history.

4

.5. Evidence for women preferring symmetrical

men for their gametes

The fact that more symmetrical men have more mates

might not be explained by GGSS exclusively. More sym-

metrical men could be advantaged because of the superior

material benefits more viable males typically provided in

the EEA or because they have success in intrasexual com-

petition (Kirkpatrick & Ryan 1991). However, additional

evidence (reviewed in sects. 4.5.1–3) suggests that these

alternative selectional processes cannot fully explain the

greater short-term mating success of more symmetrical

men. This evidence suggests that women’s preferences for

more symmetrical men may be specifically “designed” to fa-

vor their gametes.

4.5.1. Female orgasm and sperm retention. Baker and

Bellis (1995) have conjectured that women’s orgasms

evolved to manipulate sperm competition via differential

sperm retention. If male extra-pair mates in the EEA pro-

vided advantages to offspring above and beyond the invest-

ment and tangible resources they offered (through good

genes or genetic diversification: see Smith 1984), selection

could have favored adaptations that biased sperm competi-

tion in favor of conceptions with extra-pair mates who had

higher genetic fitness. Baker and Bellis (1995) report that

women who have both an in-pair (primary) partner and an

extra-pair partner have patterns of orgasms that facilitate

the retention of sperm from the extra-pair partner.

If Baker and Bellis are right, indicators of a partner’s ge-

netic fitness should be cues that lead women to have more

frequent sperm-retaining orgasms during extra-pair sex.

Thornhill et al. (1995) correlated women’s frequency of or-

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Gangestad & Simpson: Evolution and human mating

gasm during sexual intercourse with their current mate’s

FA, while controlling for his SES, anticipated future salary,

age, and observer-rated physical attractiveness. Women ex-

perienced more orgasms if their partner was more sym-

metrical, r ϭ Ϫ.27. More important, high sperm-retention

orgasms (i.e., those occurring close to ejaculation; Baker &

Bellis 1995) were significantly correlated with the men’s de-

gree of symmetry. Aside from their partner’s physical at-

tractiveness, no other male feature correlated with the fre-

quency of female orgasms. Analyses on a larger sample have

replicated this effect (Møller et al. 1999). These findings

are consistent with GGSS and difficult to explain in terms

of other theories. (For evidence that female orgasm favors

dominant males in Japanese macaques, see Troisi & Carosi

tiveness and physical prowess when evaluating them for

possible short-term relationships. Scheib (1999) found that

women place greater emphasis on physical attractiveness

when evaluating men as extra-pair partners.

Gangestad et al. (1999a) examined women’s mate pref-

erences by asking them to rate men who had been video-

taped during an interview conducted by an attractive

woman. After observing each man, women rated his attrac-

tiveness as a potential long-term mate and short-term mate

(either as a one-time sex partner or as an extra-pair mate).

Women’s sociosexual orientation (based on their Sociosex-

ual Orientation Inventory [SOI] score; Simpson & Ganges-

tad 1991a) was measured as well. Women with an unre-

stricted sociosexual orientation are more willing to have

short-term relationships (i.e., they are more interested in

short-term mating). Women with a restricted sociosexual

orientation, in contrast, are less willing to have sex without

commitment and emotional closeness (i.e., they are more

interested in long-term mating; see Simpson & Gangestad

1991a; 1992).

1

998.)

4.5.2. Women’s olfactory preferences across their repro-

ductive cycle. If women tend to choose extra-pair partners

for their gametes, compared to sex with their primary part-

ners, women’s extra-pair sex should occur during the most

fertile time of their reproductive cycles. Bellis and Baker

Compared to restricted women raters, unrestricted

women raters preferred more symmetrical men, particu-

larly for short-term relationships. Indeed, unrestricted

women’s short-term mate attractiveness ratings correlated

.40 with men’s symmetry. Correlations between restricted

and unrestricted women’s ratings of long-term mate attrac-

tiveness and men’s symmetry, as well as correlations be-

tween restricted women’s ratings of short-term mate at-

tractiveness and men’s symmetry, were all nonsignificant.

These findings indicate that more symmetrical men have

(or display) features that are preferred in short-term mates

by those women who are most willing and likely to engage

in short-term mating – unrestricted women. They also clar-

ify how women’s preferences may produce greater sexual

success in more symmetrical men. These results would not

be expected if more symmetrical men offered superior ma-

(

1990) found preceisely this pattern in a sample of British

women. If women’s patterns of extra-pair sex thus favor the

sperm of extra-pair mates, this effect might be mediated by

women’s preferences for specific attributes valued in extra-

pair partners, especially those associated with symmetry.

Olfactory cues affect mate preferences strongly in many

species (Alcock 1993). Based on evidence that women’s

olfactory sensitivities and preferences change across the

menstrual cycle (Grammer 1993), Gangestad and Thornhill

(

1998b) hypothesized that women should find the smell of

more symmetrical men more appealing during ovulation.

Men were measured for FA and then asked to wear a non-

scented T-shirt for two nights. Women smelled each shirt

(

blind to all other characteristics of the men), and rated how

attractive they found the odor of each shirt. Women’s fer-

tility was estimated from their probability of conception

when they participated in the study, based on medical data

7

terial benefits in long-term relationships.

(

Jöchle 1973). Women taking oral contraceptives were ex-

cluded from the analyses. The shirts worn by more sym-

metrical men were rated as smelling better than those worn

by less symmetrical men, but only among women who were

in the fertile phase of their reproductive cycle, r ϭ Ϫ.30.

Indeed, women’s probability of fertility correlated .54 with

their preferences for the scents of more symmetrical men.

This effect has been replicated in a larger, separate sample

5. Strategic pluralism

According to the model we have presented, men’s alloca-

tion of effort to short-term mating during evolutionary his-

tory should have been contingent on their ability to satisfy

the short-term mate preferences of women. Women’s

short-term mate preferences, in turn, should have been in-

fluenced by GGSS. Thus, men’s tendency to engage in

short-term mating should be a direct function of their ge-

netic fitness (indexed by FA), whereas men’s propensity to

invest in single, exclusive long-term relationships should be

inversely related to their genetic fitness.

(

Thornhill & Gangestad 1999), where the correlation be-

tween fertility risk and preference for the scents of sym-

metrical men was .42. Statistically controlling for a number

of factors (e.g., men’s number of showers) increased the ef-

6

fect size. These results confirm a very specific prediction

that can be derived only from GGSS and provide further

evidence about the proximate cues that may “advertise”

male symmetry.

5

.1. FA and attitudes toward engaging in casual sex

Simpson and Gangestad (1991a) developed the Sociosexual

Orientation Inventory (SOI) to measure individual differ-

ences in willingness to engage in sex without closeness and

commitment. If asymmetrical men have less desire to en-

gage in short-term sex, as our model of conditional strate-

gies predicts, men’s FA should correlate negatively with the

SOI. As predicted, the mean correlation across several sam-

ples is Ϫ.20. Men’s SOI scores do not correlate with either

the SES of their family of origin or their expected salary in

five years.

4.5.3. Women’s long-term and short-term mate prefer-

ences. Buss and Schmitt (1993) claim that the characteris-

tics women prefer in long-term and short-term mates are

quite similar. According to SST, women use short-term

mating to evaluate men as potential long-term partners or

for mate-switching. Women’s long-term and short-term

mate preferences are not identical, however. As discussed

earlier, even Buss and Schmitt (1993) have found that

women place greater emphasis on men’s physical attrac-

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5

.2. FA and investment in an exclusive relationship

available from long-term mates. Moreover, long-term

mates who offered more genetic benefits may have pro-

vided fewer material benefits. Because of variation in their

circumstances (discussed in sects. 5.6 and 5.7), women

should have differed in the extent to which they could have

benefited from obtaining genetic versus material benefits.

If some women could have appreciably improved their fit-

ness by mating with men who offered better genetic ben-

efits, these women should either have preferred long-term

mates who had markers of genetic fitness or they should

have engaged in short-term mating (especially opportunis-

tic extra-pair matings) with males who had such indicators,

even if it meant “trading-off” or risking the loss of mater-

ial benefits they could have garnered from a long-term

mate. Conversely, if other women could have enhanced

their fitness by obtaining mates who provided (or could

provide) superior material benefits, these women should

have pursued long-term mates who were able and willing

to provide the material benefits they most needed. Such

women should have refrained from extra-pair mating, sac-

rificing some genetic benefits they might otherwise have

obtained. The differential value of genetic versus material

benefits across women should accordingly have produced

In a sample of long-term dating couples, Gangestad and

Thornhill (1999b) tested whether more symmetrical men

tend to make less of an investment in their ongoing rela-

tionships. Partners answered questions about their own

and their partners’ behavior in their relationships and then

completed the Relationship-Specific Investment Inventory

(

RSI: Ellis 1998). The RSI measures 10 sets of acts perti-

nent to the partner and relationship maintenance: Being

Expressive/Nurturing, Being Committed, Giving Time,

Being Sexually Proceptive, Investing Money, Being Hon-

est, Providing Physical Protection, Being Attentive in Social

Contexts, Having a Good Relationship with the Partner’s

Family, and Not Sexualizing Others. Some of these acts

(

e.g., giving time and attention to the partner) detract from

mating efforts outside the relationship. These acts, there-

fore, should correlate negatively with men’s symmetry.

Path analyses tested models in which both self-reports

and partner reports were treated as markers of men’s in-

vestment. When men’s resource potential (indexed by their

anticipated future salary), women’s rated physical attrac-

tiveness, and women’s level of investment in the relation-

ship were controlled, more symmetrical men provided less

investment than did less symmetrical men, ␤ ϭ .26. More

symmetrical men were particularly less honest with their

partners, sexualized other women more, and spent less time

with their partners. This pattern of lower investment should

facilitate efforts to mate with women outside the current re-

lationship.

8

adaptive variation in women’s mating tactics. (For a re-

lated discussion on avian mating, see Petrie & Kempanaers

1

998.)

5.4. Evidence that differential valuation of men’s

attributes predicts women’s mating

The one component of investment that symmetrical men

provided more of was physical protection, particularly their

reported ability (as opposed to their reported willingness)

to provide their current partner with greater physical pro-

tection. Because the ability to provide physical protection

may involve the development of attributes that are also use-

ful in intrasexual competition, providing this form of in-

vestment is not likely to interfere with men’s short-term

mating. If men who possess markers of good genes do

In section 4.5.3 we described a study examining women’s

preferences for men’s symmetry in long-term and short-

term mating contexts (Gangestad et al. 1999a). It showed

that women with a less restricted sociosexual orientation

(i.e., more willing to have short-term sexual relationships)

found symmetrical men more attractive, particularly as

short-term mates. These results indicate that variation in

women’s willingness to engage in short-term mating is as-

sociated with – and perhaps driven by – their stronger pref-

erence for indicators of genetic fitness in men.

“compensate” their partners with some kind of material

benefits, the most likely candidate is physical protection.

Hrdy (1981) and Smuts (1985) have claimed that physical

aggression from men other than fathers may have been one

of the major dangers to offspring in the EEA . To reduce

these threats, women may have either mated with multiple

partners to confuse paternity or developed male-female

friendships, particularly with socially and physically domi-

nant men. Mesnick (1997) and Wilson and Mesnick (1997)

have recently argued that women may have evolved to

prefer protective males primarily to receive protection

from other aggressive males, which could have enhanced

women’s fitness directly.

Several additional lines of evidence also suggest that

women who engage in short-term mating especially prefer

men who display indicators of genetic fitness. First, women

who are willing to engage in short-term mating (i.e., unre-

stricted women) care more about a man’s physical attrac-

tiveness than do women who are less willing to engage in

short-term mating (Simpson & Gangestad 1992). Second,

when given a choice between dating a romantic partner

who is very attractive but not highly reliable/loyal versus

one who is highly reliable/loyal but only average in attrac-

tiveness, women who are more willing to engage in short-

term mating (unrestricted women) tend to choose the more

attractive/less reliable male, whereas women who are less

willing to engage in short-term mating (restricted women)

tend to choose the less attractive/more reliable one (Simp-

son & Gangestad 1992).

5.3. Variation in women’s mating strategies

Thus far we have concentrated on adaptive variation in

men’s sexual tactics. However, women also vary consider-

ably in their openness to, and willingness to engage in,

short-term mating (Simpson & Gangestad 1991a). We now

address adaptive reasons for this variation.

5.5. Environmental factors and sexual strategies

According to the model we have presented, the attri-

butes that made men valuable as short-term mates in the

EEA may have differed from those that made them valu-

able as long-term mates. Short-term or extra-pair mates

should have offered genetic benefits that were often un-

Our model suggests that women should vary in their “ex-

change rate” between a partner’s genetic fitness (indexed

by FA) and his investment, whereas men should vary in

their “exchange rate” between short-term mating effort

and long-term parental investment. Environmental factors

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Gangestad & Simpson: Evolution and human mating

should influence women’s assessments of the exchange rate

between a prospective male’s parenting qualities and his

heritable fitness. In environments where biparental care

was crucial to infant survival, male parenting qualities

should have had more beneficial effects (Andersson 1994)

Conversely, in environments with prevalent pathogens,

male genetic fitness may have had more beneficial effects

individuals place less weight on these attributes in environ-

ments containing more pathogens. Whether these findings

reflect the increased value of physical attractiveness or an

independent devaluation of these male attributes remains

unclear.

Third, in environments where pathogens are more

prevalent, women should trade off indicators of good genes

for exclusive paternal investment. In other words, a higher

degree of polygyny should be seen in pathogen-prevalent

environments (see Gangestad 1993). Low (1990a) corre-

lated the degree of polygyny with parasite-prevalence in

nearly 200 societies of the Standard Cross-Cultural Sample

(Low 1988; 1990a; Murdock & White 1969). With latitude

and geographical region held constant, polygyny was more

common in societies where pathogens were more preva-

(

because of both the importance of pathogen resistance and

the decreased marginal value of heavy parental investment

when mortality rates are high; see Kaplan 1996). If ances-

tral women were repeatedly exposed to these contrasting

environments, they should have evolved to make trade-offs

between investment qualities and indicators of good genes

contingent on specific environmental conditions. Factors

that influenced this exchange rate may have differentiated

1

0

(

a) populations of individuals, producing differences in the

lent. Hence, variation in parasite prevalence might be

partially responsible for the variation in desired mate at-

tributes and associated mating strategies across cultures

(see Tooby & Cosmides 1992).

mating systems across different groups of women (i.e.,

within different cultures; see Tooby & Cosmides, 1992, on

“

evoked culture”), and (b) women within a population, pro-

ducing differences in the mating preferences and behaviors

of women in a given group of people.⁹

5.6.2. Factors influencing the value of men’s parental ef-

fort. Several factors should also have played a part in de-

termining the influence of men’s parental effort on infant

mortality and their later reproductive success. For example,

in environments where the primary causes of infant mor-

tality were infectious diseases (rather than inadequate

parental care), paternal effort should have had less impact

on offspring fitness. In contrast, when infant viability was

strongly tied to biparental care (e.g., when women could

not provide for all the nutritional needs for their offspring),

paternal care should have had a greater impact on offspring

fitness.

5.6. Environmental factors producing differences

between populations

5.6.1. Factors influencing the value of men’s genetic

quality. Several factors may have affected the value of men’s

genetic fitness. According to principles of host-parasite

coevolution (Hamilton 1982), pathogen prevalence should

have been one critical factor. In environments where

pathogens were prevalent, women should have benefited

more from mating with men who had good genetic quali-

ties that made them more pathogen resistant. Although ad-

ditional work is needed, several lines of research are con-

sistent with this notion.

First, besides conveying information about female fertil-

ity, physical attractiveness may also contain cues about a

person’s health, pathogen resistance, and perhaps genetic

fitness (Symons 1979). Gangestad and Buss (1993) tested

whether preferences for attractive mates might have

evolved through parasite-driven sexual selection. Men and

women from 29 countries around the world rated the im-

portance of several mate attributes, including their prefer-

ence for a “good-looking” mate (see Buss 1989). Pathogen

pressure at each geographical location was estimated from

information about the prevalence of eight different para-

sites (see Low 1990a). Across the 29 countries, both men

and women in regions containing more pathogens placed

greater importance on a prospective mate’s attractiveness,

even when latitude, geographical region, and mean income

were controlled, partial r ϭ .76. This finding does not of

course demonstrate that host-parasite coevolution neces-

sarily influenced sexual selection in humans. Attractiveness

could have been more important in regions with more par-

asites because of direct selection against mating with dis-

eased individuals (Kirkpatrick & Ryan 1991).

Women’s access to resources should also have influenced

their need for – and the value of – male parental investment

(Gowaty 1992a; 1992b). Because parental investment often

has diminishing marginal returns (see Cashdan 1993),

men’s resources may have been less important when

women had sufficient resources of their own. Hence, poly-

gyny should be more prevalent in societies in which women

have more access to resources. Low (1990b) correlated in-

dicators of women’s ability to care for both themselves and

their infants independently with measures of polygyny

across nearly 200 cultures in the Standard Cross-Cultural

Sample. As predicted, polygyny is more common in cul-

tures where women have more control over resources.

We do not know how women’s control over resources in

ancestral environments affected their mate preferences,

but their participation in current economies does predict

the importance women place on physical attractiveness in

men. In the cultures surveyed by Buss (1989), women’s

mean preference for physical attractiveness in a mate was

positively correlated with the proportion of women who

were involved in the economy. However, women’s prefer-

ences for qualities related to parental care did not correlate

with their economic participation (Gangestad 1993).

Across the cultures surveyed by Buss (1989), Eagly and

Wood (1999) have found that women’s preference for men’s

earning potential is predicted by a measure of women’s

“empowerment” (United Nations Gender Empowerment

Measure; United Nations Development Programme 1995).

As women’s empowerment (indexed by their earnings, their

representation in legislative government, and their involve-

ment in professional positions) increases relative to men in

cultures, women place increasingly less value on the earn-

Second, women in pathogen-prevalent environments

should be more willing to trade off features associated with

exclusive parental care. Indeed, across the 29 cultures,

parasite prevalence correlated negatively with the mean

ranked importance of 4 attributes relevant to direct and

exclusive parental care: “dependable character,” “pleasing

disposition,” “emotional stability and maturity,” and “desire

for home and children,” r ϭ Ϫ.41 (Gangestad 1993). Thus,

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Gangestad & Simpson: Evolution and human mating

ings of a mate. However, women do not place less empha-

sis on men’s physical attractiveness (nor do men place less

emphasis on women’s attractiveness) as women’s empower-

ment increases. Although Eagly and Wood interpret these

findings in terms of domain-general behavioral processes

and responses to gender roles, they are also consistent with

an ecologically contingent, conditional mating strategy in

which women moderate their mating tactics and prefer-

ences in response to specific environmental inputs (e.g.,

women’s control of resources; see Low 1990b).

value different qualities in mates. In many circumstances,

parental investment has decreasing marginal returns: the

more investment an offspring has received, the less benefi-

cial the next “dose” (see, e.g., Cashdan, 1993; for important

exceptions, see Kaplan 1996). Especially when men’s and

women’s investments in offspring are similar (rather than

complementary) in form, women who can make more of an

investment on their own show less of a need for additional

paternal investment. Consequently, women may have

evolved to focus more on a man’s genetic fitness when their

own access to independent resources increased (Gowaty

1992a), making them more willing to engage in short-term

mating.

Correlations between women’s sociosexual orientation

and their personality traits provide indirect support for

these conjectures. Unrestricted women (who are more

likely to engage in short-term mating) tend to be more so-

cially dominant, more extroverted, and less harm-avoidant

(Gangestad & Simpson 1990). Each of these traits should

facilitate the acquisition and maintenance of independent

resources. Hrdy (1981) and Gowaty (1992a) have suggested

that women’s access to resources through cooperation,

competition, and social influence should have been an in-

tegral component of their fitness in the EEA. These per-

sonality traits may have helped unrestricted women acquire

their own resources and, thus, pursue short-term mating

tactics.

5.6.3. Effects on men’s tactic choice. How women evalu-

ate men and how they make trade-offs should influence

which mating tactics men adopt. In environments where

male parenting qualities are needed and valued, women

should be less likely to engage in short-term and extra-pair

mating. In response to this, men should devote greater ef-

fort to parental investment, and variance in men’s repro-

ductive success should be reduced (i.e., a larger proportion

of men should have offspring). On the other hand, in envi-

ronments where men’s genetic fitness is needed and valued,

women should be more willing to pursue short-term mat-

ing. Consequently, men should devote greater effort to

short-term and extra-pair mating, and variance in men’s re-

productive success should increase (see Low 1990a;

1

990b).

In environments where biparental care is not as crucial,

even men with lower genetic fitness might benefit from

channeling some of their effort to short-term and extra-pair

mating (perhaps by attempting to “deceptively” advertise

genetic quality). Under these circumstances, men’s in-

creased efforts to display their “quality” could result in an

escalated war of attrition (Maynard Smith 1982), which

could be facilitated by testosterone-based somatic growth

and aggressive behavioral displays. Thus, the fiercest intra-

sexual competition among men may not occur over re-

sources relevant to parental investment, as SST might pre-

dict. Rather, it may occur when status displays that signal a

male’s genetic fitness are contested (see Daly & Wilson,

Based on these notions, one might expect the value

women ascribe to their mates’ resources to diminish as their

own access to resources increases. This association has not

been found: Women with high-paying jobs tend to value re-

sources as much as or more than women with lower paying

jobs do (e.g., Buss 1989; Townsend 1989; Wiederman &

Allgeier 1992). These findings contrast with those of Eagly

and Wood (1999), who found that, across cultures, women’s

access to resources and power is associated with a lower

rated importance of mates’ financial success. Because what

women learn about the value of a mate’s resources is shared

within a culture, the effects of women’s access to resources

within a culture may differ from the effects of women’s ac-

cess to resources across cultures (see Eagly & Wood 1999).

Another possibility is that Eagly and Wood’s finding is not

the result of women’s access to monetary resources (only

one component of the Gender Empowerment Measure

they used) but to their access to power. Power and the abil-

ity to affect outcomes through social influence may have

been important facets of women’s circumstances for which

they evolved contingent strategies, whereas their ability to

accumulate wealth in modern cash economies may not have

been.

In sum, environmental factors should influence women’s

mating tactics. Pathogen prevalence, for example, should

increase the value women place on men’s genetic quality,

whereas the need for biparental care should increase the

value they place on men’s parental effort, particularly for

women who do not have independent access to resources.

Depending on environmental conditions, therefore, women

should make trade-offs between male genetic quality and

parental investment in adaptive, ecologically contingent

ways. Women should vary in the exchange rate between

men’s genetic quality and their long-term investment, where-

as men should vary in the exchange rate between short- and

long-term mating. As a result, most men should adjust their

mating strategies in response to what women value.

1

988, for a discussion of how men’s face-saving tactics often

lead to homicide).

5.7. Environmental factors producing differences

within populations

5.7.1. Differences caused by differential exposure to cues

signaling the value of parenting. If some women are ex-

posed to environments that require paternal investment

whereas others are not, within-population differences in

mating preferences and tactics should emerge. Belsky et al.

(

1991) have proposed that patterns of parental care experi-

enced during childhood may affect adult mating tactics (see

also Chisholm 1996; Simpson 1999). Insufficient parental

responsiveness to their needs as infants (possibly caused by

harsh, demanding environments) should lead individuals

to adopt short-term mating tactics better suited for envi-

ronments in which stable pair-bonds are not needed or

anticipated. Conversely, adequate parental responsiveness

should result in long-term adult mating tactics more ap-

propriate for environments in which biparental care and

stable pair-bonds are needed and expected.

5.7.2. Differences due to women’s phenotypic qualities.

Women’s personal characteristics may also lead them to

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Gangestad & Simpson: Evolution and human mating

. Summary and conclusions

6

NOTES

1

. Not all environment-response linkages are evolved. Many

Mating tactics are highly variable in both men and women

and have evolved to be contingent on environmental fac-

tors. Complete theories of mating strategies must account

for these individual differences and contextual effects. We

have proposed that these phenomena cannot be fully un-

derstood without considering the nature of the trade-offs

that underlie mating decisions in humans. We suggest that

good gene sexual selection, in concert with good-parenting

sexual selection, may have generated the variation and con-

textual effects associated with the short- and long-term

mating tactics witnessed in both sexes.

are learned. Learning, however, can reflect a set of implicit,

evolved decision rules (see Mayr 1974).

2. In certain species, males engage in more parental effort than

females, in which case sexual selection pressures operate more

strongly on females than males (Trivers 1972). The selection pres-

sures that lead to different amounts of parental effort for the sexes

are not yet fully understood (for one treatment, see Parker et al.

1

972). Moreover, as we will discuss, there are circumstances in

which mating with multiple mates can benefit females even in

species in which they invest in offspring more than males do (see

also Hrdy 1981).

3. These effect sizes may be attenuated by unreliable mea-

surement, particularly for single-item measures. Our 3-item mea-

sure of attitudes toward casual sex has a reliability of nearly .8

Given the demands of biparental care during evolution-

ary history, both men and women were selected to use

long-term mating tactics and invest in offspring. However,

they were also selected to use ecologically contingent, con-

ditional mating strategies, dedicating some effort to short-

term and extra-pair mating under specific conditions.

Women may have evolved to trade off evidence of a man’s

genetic fitness for evidence of his ability and willingness to

invest in offspring. The specific mating tactics and prefer-

ences women adopted, however, depended on the nature

and quality of their local environment. If the local envi-

ronment was difficult and demanded biparental care,

women placed more weight on the investment potential of

prospective mates and less weight on indicators of their

genetic fitness. As a result, a larger proportion of women

adopted long-term mating tactics almost exclusively. If, on

the other hand, the pathogens were prevalent in the local

environment (or the environment signaled the importance

of the genetic fitness of offspring), women placed more

weight on indicators of the genetic fitness of prospective

mates. In such environments, a larger proportion of

women were willing to engage in short-term, extra-pair

matings, allowing them to gain genetic benefits from men

who provided less parental investment at the risk of losing

parental investment from their primary mates. The mating

tactics and preferences of women accordingly reflected

the nature and quality of the environments in which they

lived.

Whereas women “tracked” their environment, men

tracked and adjusted their mating tactics and preferences

to the behavior of women (Thiessen 1994). If most women

expected heavy paternal investment, most men (especially

those who displayed less fitness) offered more and per-

haps exclusive parental investment, dedicating a greater

portion of their effort to long-term mating tactics and

parental investment. As a result, variance in men’s mating

success was reduced. If women’s “demand” for genetic

benefits increased, some men (especially those advertis-

ing such benefits) dedicated more effort to short-term, ex-

tra-pair mating tactics, thereby increasing variance in mat-

ing success among men. Only a small proportion of men

(

Simpson & Gangestad 1991). If sex accounts for 8%–20% of the

variance in this measure, it should explain 10%–25% of the vari-

ance in an error-free measure. Single items in this domain may have

as little as 50% reliable variance (estimated using the Spearman-

Brown formula; Anastasi & Urbani 1998). Hence, sex may account

for 20%–40% of the reliable variance underlying single-item mea-

sures of optimal number of future sex partners and willingness to

have sex with an unknown partner. Naturally, the reliable variance

in these measures may not all be valid, as some may reflect dif-

ferences in social desirability responding. The sex difference in

Clark and Hatfield’s (1989) naturalistic field study of willingness

to engage in unsolicited sex with a stranger (using a measure less

susceptible to social desirability than lab measures) was one of the

largest effects ever documented, accounting for about 60% of the

variance. One possible reason this sex difference is so large is that

men are willing to accept unsolicited sex even when they are not

exerting effort to obtain short-term mates. The robustness of this

result needs to be replicated, however. Moreover, this sex differ-

ence may partly reflect differences between men and women in

the fear of physical harm from opposite-sex strangers rather than

differences in interest in short-term mating per se (see Hrdy

1997). Overall, although sex accounts for a large amount of the

variance in measures of interest in and willingness to actively pur-

sue short-term mating, it appears to explain less variance – in

some cases substantially less – than occurs within each sex. (For

comparison purposes, sex accounts for about 50% of the variance

in adult height.) Moreover, the distributions of men’s and women’s

interest in pursuing short-term, opportunistic matings appear to

overlap substantially.

4

. The CV is evolutionarily relevant because the potential rate

a

of evolution (“evolvability” or the proportionate change in a char-

acter’s mean in the population per generation) is a function of the

absolute amount of genetic variance (specifically, the square of the

CV ). The sheer amount of environmental variance in a trait does

a

not affect the rate of the trait’s evolution. The heritability of a trait

is its genetic variance divided by total (genetic plus environmen-

tal) variance. Because this measure standardizes a trait’s genetic

variance (relevant to its evolvability) in relation to its environ-

mental variance (not relevant to its evolvability), heritability is a

less evolutionarily relevant index than the CV . Fitness characters

a

tend to have lower heritabilities (around .25 on average; Mousseau

& Roff 1987) than ordinary morphological traits do, but not be-

cause they have low genetic variance. Rather, they tend to have

very high genetic variance, as well as very high environmental vari-

ance. Because fitness characters have very high genetic variance,

they have more potential to evolve than ordinary morphological

traits do, despite lower heritabilities (Houle 1992).

(

i.e., those who displayed the most fitness) were able to

carry out short-term tactics successfully at all times, re-

gardless of the environmental factors to which women

were responding.

5

. The fluctuating asymmetry of an individual trait (e.g., ear

Many of the unique predictions derived from this model

have been supported by recent empirical data. Although

our notions extend our understanding of the strategic plu-

rality of human mating in many ways, this account of the ties

between evolutionary theory and human mating strategies

remains far from complete.

width) is often a very weak indicator of underlying developmen-

tal imprecision (Gangestad & Thornhill 1999a). Even the com-

posite FA measure (which consists of 10 aggregated traits, and

was used in many of the human studies we cite) is estimated to

correlate only about .5 with underlying developmental impreci-

sion. This makes the modest associations between FA and other

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6

Commentary/Gangestad & Simpson: Evolution and human mating

traits (e.g., mating success; Møller & Thornhill 1998) all the more

Strategic Pluralism Theory (SPT) provides a much needed cor-

rection for the overly simple idea that evolution will have a pre-

dictable and consistent effect on human mating strategies. Under

this simplistic view, men are expected to be promiscuous and to

compete for women, whereas women should select mates from

numerous competitors and value monogamy. Instead, SPT pro-

poses that mating strategies will vary according to environmental

conditions. Such variation accounts for a range of mate prefer-

ences and mating strategies being used by both men and women,

and leads us to expect women to compete for men as well as vice

versa. I believe the authors make a convincing case for SPT, pro-

viding evidence that is particularly remarkable when one consid-

ers that cultural influences on mating are certain to overlay, and

could mask, any evolutionary tendencies. Still, there are additional

complexities that, if incorporated within SPT, may make this the-

ory an even better predictor of mating tactics and preferences.

As a prelude to these comments, it should be noted that sexual

selection should not always be biased towards either “good-

parenting” or “good-genes,” in part because these are not nega-

tively correlated traits. For instance, size and strength are cues to

good-genes in males but also indicate good-parenting as in the

greater ability to defend infants. It appears that there are two

somewhat distinct sets of “signs” or “cues” that can be used to eval-

uate these traits (e.g., fluctuating asymmetry for good-genes but

not for good-parenting) and would suffice to allow a pluralism of

strategies. Nonetheless, males should always value both traits, to

some extent, since both signal increased probability of genetic

transmission (i.e., more viable offspring and better parental care).

While good-parenting cues may be irrelevant to a female pursu-

ing short-term mating, the ideal long-term partners would be high

on both traits.

impressive.

6. It could be argued that women find more symmetrical men

more appealing because they are looking for long-term mates who

will provide them (and subsequent offspring) with greater mater-

ial benefits. Even though more symmetrical men may be more ca-

pable of providing certain benefits (e.g., physical protection), the

reproductive cycle studies indicate that women find the smell of

more symmetrical men more desirable primarily when they are

ovulating (that is, when gaining material benefits is not an issue).

From the standpoint of adaptive design, these data strongly sug-

gest that women find symmetrical men more attractive than less

symmetrical men for reasons beyond potential resource acquisi-

tion.

7. We are not suggesting that obtaining “good genes” from cer-

tain men is the only possible fitness benefit of short-term mating

available to women. Buss and Schmitt (1993), for example, have

proposed that some women may use short-term mating to evalu-

ate and attract long-term mates. The evidence we present, how-

ever, provides support for the former function.

8. Because women also vary in their relative mate value, they

should differ in the amount of benefit they receive from men. Cer-

tain highly valued women may be able to obtain both high mater-

ial benefits and high genetic benefits. For most women, however,

the genetic benefits and exclusive investment benefits that can be

obtained from mates should correlate negatively within the most

desirable set of mates a women can attract (Gangestad 1993).

9. Previously, we suggested that women’s relative evaluation of

genetic benefits and material benefits may partly reflect geneti-

cally polymorphic, alternate strategies (see Gangestad & Simpson

1

990). Although this possibility remains plausible, variation in

women’s mating strategies may be more strongly governed by en-

vironmental conditions that moderate the relative value of genetic

versus material benefits.

Whereas SPT is quite cognizant of individual differences in po-

tential mates (especially their genetic fitness and, in the case of

males, their likely parental investment), the theory as presented is

insufficiently attentive to important individual differences among

the “selectors” (i.e., the individuals expressing mate or mating

preferences). Specifically, the competence of “selectors” should

modify the valuation of traits in potential mates and the strategy

pursued. “Competence” is used here in a broad sense to refer to

health, physical prowess, cognitive ability, and other traits that de-

termine individuals’ ability to fend for themselves and their off-

spring. The more competent a woman is in this sense, the more

risk she can take in the form of extra-pair mating, because losing

a mate due to detection of infidelity is less likely to harm her chil-

dren. Likewise, the parental contributions of mate(s) will have less

value for more competent women, so such women are likely to

place a relatively high value on genetic fitness rather than on good-

parenting. More competent males, by virtue of being able to be

good providers with less cost (e.g., proportionately less expendi-

ture of resources) and/or being better at deception, may be more

likely to pursue short-term mates while at the same time main-

taining long-term mating(s). Similarly, in good environments,

males with highly competent female partners will be able to put

more effort towards additional sexual relationships without re-

ducing overall parental investment to a harmful level (cf. Cashdan

1

0. Low (1990a) suggests that healthy men in pathogen-

prevalent regions may have multiple mates because they can pro-

vide better paternal care. We suggest that men who have better

fitness indicators should invest less in their offspring than men

with poorer indicators.

Open Peer Commentary

Commentary submitted by the qualified professional readership of this

journal will be considered for publication in a later issue as Continuing

Commentary on this article. Integrative overviews and syntheses are es-

pecially encouraged.

1

993).

Age is a detectable factor that will be correlated with compe-

Variation in optimal human mating strategies:

Effects of individual differences in

competence and self-regulatory mechanisms

tence. Given the very long period of dependency in human off-

spring, younger women are more likely to live long enough to raise

a child. Older women become increasingly less likely to survive

childbirth and to have various reproductive complications (cf. Ales

et al. 1990). In addition, older women and men are more likely to

have reduced competence due to a longer period of exposure

to parasites, accidents, and other risks. Thus, aging should tend to

modify the optimal mating strategy of women, making them in-

creasingly concerned with paternal ability and investment. More

generally, the fewer additional offspring a woman can, or is likely,

to produce, and the more challenging the conditions for success-

fully rearing children, the more that woman should be concerned

with the good-parenting indicators in potential mates. This shift is

Thomas R. Alley

Department of Psychology, Clemson University, Clemson, SC 29630

alley@clemson.edu

Abstract: Several suggestions are made for revision of Strategic Pluralism

Theory (SPT). One revision requires recognition of the impact of individ-

ual differences in cognitive and behavioral competence on optimal mating

strategy. In addition, SPT may need to incorporate certain self-regulatory

processes such as the impact of widespread valuation of mates with one

trait on their availability.

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Commentary/Gangestad & Simpson: Evolution and human mating

analogous to that seen along the continuum of r- to K-selection in

inter-species comparisons (Pianka 1970).

differences. For example, the effect sizes quoted for sex differ-

ences in preference for multiple sex partners were expressed as

proportions of the variance accounted for. Meta-analysts (e.g.,

Eagly 1995; Rosenthal 1990) have argued that this is a misleading

way of expressing magnitude of effects, not only because it is (as

indicated in note 3) subject to measurement error, but also be-

cause relatively small proportions of the variance in important at-

tributes can have large effects in practice. When converted into

the statistic more commonly used in meta-analyses, effect size (g),

the differences cited ranged from .58 to 1.01, all of which are re-

garded as large effects for the social sciences generally (Cohen

1988). As acknowledged, these effect sizes were found in ques-

tionnaire studies, where they are likely to be attenuated by social

desirability and measurement. Again, as acknowledged (in note 3),

the more ecologically valid study of Clark and Hatfield (1989)

found a massive sex difference in preference for multiple sex part-

ners. In order to emphasise within-sex variation, it is not necessary

to play down sex differences by citing them in terms of proportion

of the variance accounted for. Sex is after all another alternative

reproductive strategy, and there are clear principles why we would

expect men and women to be different in their reproductive and

social behavior.

In addition to the variations in individuals’ competence, other

factors should be added to SPT as presented in the target article.

One such factor is the support/resources provided by one’s social

web. For instance, females with additional support for child-care

from their mothers or others may safely reduce the time and ef-

fort expended on child rearing (Fairbanks 1993) or, perhaps, place

reduced value on good-parenting when selecting mates.

Another missing factor is the self-regulatory processes that are

likely to influence optimal strategies. For example, if adverse en-

vironmental conditions increase the desirability of men with signs

of good-parenting, there will be more competition for such men.

Assuming a balanced sex ratio in the population, men high on

parental caregiving will become scarce (already mated) while

there should be lowered competition for men with apparently

good genes. Consequently, the optimal strategy for some women

will change as the population of unmated males shifts, with men

higher on good-genes becoming more available. The end result for

SPT, however, is unclear. For one thing, these self-regulatory

mechanisms are likely to affect behavior but should not alter pref-

erences. Women should still prefer men high on good-parenting

but may not be able to select (“catch” or find) one. More impor-

tant, the strategy pursued by one sex should tend to alter that used

by the other. In this case, if most women are putting a high valu-

ation on good-parenting, more males can be expected to display

good-parenting since for many males this will be a more effective

mating strategy. (For the opposite case, note that it is not possible

to alter one’s signs of good-genes, with the exception of grooming

and related activities that have limited effectiveness.) Certainly

some complex web of self-regulatory processes can be expected

that includes both intra- and inter-sexual adjustments.

The answer to the question posed in section 2.4 (why all men

do not pursue short-term matings) was answered by Symons

(1979) thus: because women do not let them. On this view, it is not

that most men adopt a long-term strategy in preference to a short-

term strategy; it is that most men do not have the opportunity to

pursue short-term strategies, but they would if they could. The

brain surgeon analogy does not fit this example, since being a brain

surgeon requires talent and training, whereas switching from a

long to a short term strategy only requires opportunity.

In G&S’s discussions of within-sex strategies, it was not al-

ways clear whether these were situation-dependent (conditional)

strategies, or – as their brain surgeon analogy implied – stable in-

dividual differences (alternative strategies). Alternative strategies

include the two sexes, and the morphological specializations found

within the male sex in some species (such as ruffs: van Rhijn 1974).

It would have been helpful to have distinguished between the two

at all times. For example, it was clear that women’s short-term

mating strategies were considered as conditional strategies, as was

men’s FA, but in other cases alternative, situation-dependent,

strategies seem to have been intended.

G&S refer to long and short term strategies as if these are equiv-

alent in the two sexes. The use of these terms also suggests that it

is only the duration of staying with the mate that is important,

whereas time is only relevant because it is associated with parental

investment. It is the degree of parental investment that distin-

guishes reproductive strategies (Trivers 1972). Therefore high and

low investing strategies would be more appropriate labels than

short and long term. When considered in these terms, it is clear

that the two sexes cannot be regarded as equivalent. A female

mammal may be able to engage in a short-term mating in the sense

that she can then have nothing further to do with the male, but

this does not necessarily represent low parental investment by this

female. If she is impregnated, it will have been a mating with a

high future parental investment. In this sense, only a male can

truly walk away cost-free. By referring to such matings as short-

term for the female, G&S were defining the female’s strategy in

terms of the investment of the male with whom she is mating. Per-

haps this was intended; if so, it is worth further exploration, be-

cause it represents an important way in which the two sexes differ

that would have implications for characterising within-sex varia-

tions. Male and female are themselves specialised reproductive

strategies, and any consideration of further specializations within

each sex would benefit from using this as a starting-point.

As Gangestad & Simpson conclude, SPT is incomplete. The fact

that they were able to find a wide variety of empirical data to sup-

port their version of SPT may indicate that their model tends to

incorporate at least some of the most powerful operative forces.

Nonetheless, the future will produce more complex models with

better empirical support.

Strategic pluralism: Men and women

start from a different point

John Archer and Mani Mehdikhani

Department of Psychology, University of Central Lancashire, Preston, PR1

2HE, United Kingdom. {j.archer; m.mehdikhani}@uclan.ac.uk

www.uclan.ac.uk/facs/science/psychol/ja.htm

Abstract: Gangestad & Simpson’s (G&S’s) analysis of strategic pluralism

is welcomed as a balance to the current emphasis on between-sex varia-

tion. It could have been clarified by acknowledging the extent to which

males and females represent fundamentally different mating strategies,

since this affects how we view within-sex strategic variation. The distinc-

tion between conditional and alternative strategies could also have been

highlighted.

Both evolutionary and standard social science accounts of sex dif-

ferences in social behavior (e.g., Archer 1996; Eagly 1995) tend to

overlook within-sex variations. Gangestad & Simpson’s (G&S’s)

target article provides a welcome counterweight to this by con-

sidering variations among men and women as alternative or con-

ditional reproductive strategies. It is an important contribution

that has implications for a number of research areas, such as per-

sonality, mate selection, and psychological sex differences. This

commentary concerns three points: the emphasis on between ver-

sus within sex variations; the distinctions between types of alter-

native strategy; and the characterization of reproductive strategies

as short or long-term.

To highlight within-sex variation, G&S sought to play down sex

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Commentary/Gangestad & Simpson: Evolution and human mating

Accounting for female strategic variation

For example, we recently compared Australian women in the top

and bottom quintiles of a measure of sociosexuality (Bailey et al.,

in press). Those in the top quintile were much more likely than

those in the bottom quintile to have had sex with someone they

had met the same day (59% versus 6%), and they were also much

more likely to have been sexually unfaithful to a steady partner

J. Michael Bailey

Department of Psychology, Northwestern University, Evanston, IL 60208

jm-bailey@nwu.edu

Abstract: Gangestad & Simpson’s theory accounts for the existence of

male strategic variation admirably well, although it does not specify the

precise nature of the adaptation linking male developmental stability to

strategic pluralism. In contrast, female strategic variation remains elusive.

Empirical data suggest that genetic variation partly underlies such varia-

tion, but the causes of female strategic differences largely remain unex-

plained.

(

48% versus 3%). Furthermore, women who require less emo-

tional commitment from their sex partners are more demanding

in other respects, such as partners’ physical attractiveness (Mikach

&

Bailey 1999; Simpson & Gangestad 1992). This observation is

consistent with the idea that some women trade commitment for

good genes, but it leaves unanswered the question of why women

vary in the trade-offs they are willing to make.

Gangestad & Simpson (G&S) offer a compelling but ultimately in-

complete theory of strategic variation in human sexual life histo-

ries. The theory is particularly well explicated for men: Men vary

in their genetic quality, largely due to mutational pressure in the

context of parasite resistance dynamics, which impede allelic fix-

ation. Men with good genes have low levels of developmental in-

stability, and some indicators of developmental instability are de-

tectable. Women prefer men with low levels of developmental

instability, and hence such men have more mating opportunities

and can invest less in particular women. By G&S’s theory, then,

genes do not influence strategic variation via direct pathways (i.e.,

by affecting the neural substrates of sociosexuality independent of

developmental instability). Such “direct pathway” genes may ex-

ist, but they are not the kind of genes that G&S are concerned

with. Indeed, much of the genetic variation implicated by their

theory can in different contexts cause either lesser or greater de-

velopmental instability, and hence can lead to either greater or

lesser mating effort.

Although the theory is impressive in its demonstrated ability to

link ideas from evolutionary genetics with individual differences

psychology, it leaves unanswered important questions about sex-

ual strategies. For example, the theory does not provide much

guidance about the ontogeny of male strategic differences. Men

must possess an evolved program that allows them to adjust their

sexual strategies on the basis of information that is correlated with

developmental instability. The specific content of the program is

unclear, however. For example, the program might run only once,

prior to birth, with the brain somehow inferring developmental

stability and directing development accordingly – males with de-

velopmental stability directed toward mating effort and those with

developmental instability directed toward investment in their part-

ners. A more plausible alternative is that males continuously and

unconsciously monitor their ability to succeed in a high mating-

effort strategy. If so, then we would expect men’s psychology and

behavior to track relevant changes. For example, when men win

lotteries or earn millions on the stock market, their mating op-

portunities surely increase. Do their psychological preferences

change accordingly? The inability of G&S’s theory to answer such

questions does not make the theory less likely to be true, because

the theory appears to be mute with respect to ontogeny. Never-

theless, it is an important limitation of the theory.

According to G&S’s theory, male sociosexual variation is in-

evitable, because not all men can win the genetic lottery. But an

analogous account of female sociosexual variation – which G&S

do not attempt – is neither theoretically coherent nor empirically

supported. It is unclear whether the optimal strategy of women

with good genes should differ from that of other women, and no

correlates of women’s FA have been established. In their target ar-

ticle, G&S focus instead on environmental explanations of female

sexual strategies. However, the most sensible hypothesis, that

women with adequate resources can best trade investment for

good genes, is not supported by their review.

In an earlier article, Gangestad and Simpson (1990) proposed

that female sociosexual variation is maintained via frequency-

dependent selection. By this account, women with unrestricted

versus restricted approaches to casual sex have specialized to ex-

ploit different niches. Furthermore, the value of pursuing each

strategy plausibly depends on the relative frequency of women

who also pursue it. Consistent with this hypothesis, female socio-

sexuality appears to be moderately heritable (Bailey et al., in

press). The likelihood of strategic heritable variation is controver-

sial, however, because recombination prevents fortuitous combi-

nations of genes from persisting long enough for polygenic

morphs to evolve (Tooby & Cosmides 1990a). A two-strategy sys-

tem with a binary genetic switch can evolve more easily. Such a

system implies that restricted and unrestricted strategies should

be typologically distinct, but this has not yet been demonstrated.

My focus on the incompleteness of G&S’s theory should not ob-

scure the fact that the theory is an important advance. The theory

is well articulated and has generated some surprising findings.

Furthermore, it helps resolve a paradox that has been embarrass-

ing for evolutionary psychology, namely, the existence of heritable

variation in sexual strategies (Bailey 1997). This resolution is more

successful for men than for women, however.

Choice of mating tactics

and constrained optimality

William M. Baum

Department of Psychology, University of New Hampshire, San Francisco,

Another limitation of the theory is its inability to explain female

strategic variation. According to the theory, women seek both in-

vestment and good genes. However, men with the best genes of-

fer less investment than other men do, and most women are thus

forced to make trade-offs. This fits in well with their theory of

male strategic variation – so far so good. However, this observa-

tion does not necessarily lead to female strategic variation. For ex-

ample, women might have evolved a uniform mechanism to assess

men’s investment ability and genetic quality, to calculate strategic

trade-offs, and to place men on a single dimension of mate value.

By this scenario, all women would have similar preferences and

would not vary in their willingness to trade investment for genetic

quality.

CA 94108. wm.baum@unh.edu

Abstract: Gangestad & Simpson’s arguments may be rendered more sub-

stantial and precise by capitalizing on research and theory on choice be-

tween reinforced response alternatives. An analysis in terms of feedback

functions shows that the effects of individual differences in attractiveness

may be understood as constraints on optimality and may be reconciled

with the previous research and theory that the authors criticize.

Gangestad & Simpson (G&S) present a lucid and persuasive ar-

gument that male and female mating strategies should vary with

individual differences and environmental differences. Although

their general argument is well made, they could improve the char-

acterization of the factors affecting mating strategy by: (1) distin-

guishing more carefully between the effects of individual differ-

ences and environmental variation; (2) capitalizing on research

This is not our world, however. With respect to sociosexuality,

or willingness to engage in casual sex (Simpson & Gangestad

1

991a), women appear to be specialists rather than generalists.

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Commentary/Gangestad & Simpson: Evolution and human mating

and theory concerning the type of choice entailed in mating strate-

gies, and (3) reconciling their view with other views within the

context of optimality theory.

Although one may treat individual differences and environ-

mental differences in ways that look equivalent mathematically,

that is only true when one examines the behavior of individuals.

In the explanation given below, which focuses on individuals, the

various factors determining possible fitness could all be incorpo-

rated into one multivariate function. Since environmental varia-

tion is also important to understanding the behavior of groups,

however, the two should be treated separately. Given a particular

environment, one still may expect variation in individual behavior

because of individual differences, particularly in attractiveness.

G&S appear to be unaware of a large and rich body of research

and theory on choice that applies to their conception of mating

strategies (see Williams 1988, for overview; Baum 1981). If, as

they suggest, a strategy consists of a mix of tactics, with different

mixes providing different payoffs, this is modeled by concurrent

reinforcement of two response alternatives. In research on con-

current performance, two response alternatives produce rein-

forcement and the relative frequency of choosing the two is re-

lated to the relative reinforcement obtained from the two (Baum

Figure 1 (Baum). Reproductive success as a function of strategy,

expressed as proportion of long-term tactics (L) relative to long-

and short-term (S) mating effort overall. The curve labeled “High”

shows the possibilities for a more attractive individual. The curve

labeled “Low” shows the possibilities for a less attractive individ-

ual. Crosses indicate optimal strategies. The optimal strategy for

the more attractive individual includes more short-term tactics

and is higher overall than that for the less attractive individual.

1

979; Herrnstein 1961). G&S’s account parallels such a situation,

with the two alternatives being the two types of tactics and the

payoffs being in reproductive success.

If L and S are the frequencies of an individual’s pursuing long-

term tactics and short-term tactics, then the possibilities for a

given environment (prevalence of parasites, climate, etc.) still de-

pend on the individual’s attractiveness. Figure 1 shows the way an

individual’s reproductive success might vary depending on strat-

egy, defined as the proportion (p) of L out of all mating effort, L

ϩ S. If all mating effort is directed toward long-term tactics (p ϭ

1

), reproductive success attains the value shown to the extreme

mating tactics. Males and females would differ quantitatively,

however, because more short-term mating tactics would always be

better for males than females. Males’ feedback functions would lie

to the left of those for females.

In summary, although G&S’s points are well taken, they may be

represented more precisely and reconciled with earlier research

and theory if they are seen within the larger context of optimality

theory and particularly constrained optimization.

right. If all the effort is given to short-term mating (p ϭ 0), re-

productive success attains the value shown to the extreme left, as-

sumed here to be less than the other extreme, in keeping with the

authors’ hypotheses. A mix, however, produces higher reproduc-

tive success than either extreme, because the highest points on the

curves lie between the extremes. Two curves are shown, one for a

more attractive individual and one for a less attractive individual.

The curve for the more attractive individual attains its optimum at

a lesser proportion of long-term tactics, as theory and research

would predict. The curve for the more attractive individual also

reaches greater reproductive success at its optimum. These

curves, also known as feedback functions (Baum 1973; 1981),

show what is possible in the environment. An individual’s actual

performance would appear as a point on one of the functions. The-

ory predicts the point will be close to the optimum.

Mating and marriage, husbands and lovers

Stephen Beckerman

Department of Anthropology, Pennsylvania State University, University Park,

PA 16802. stv@psu.edu

Two features emerge from Figure 1. First, attractiveness func-

tions as a constraint. Each feedback function is the result of cut-

ting through a three-dimensional surface at a certain level of at-

tractiveness. The possibilities for the less attractive individual

differ from the possibilities for the more attractive individual. Sec-

ond, the more attractive individual’s feedback function cuts closer

to the global optimum for the entire surface, allowing that indi-

vidual to attain an optimum close to that overall optimum for the

environment. That global optimum includes more short-term

mating than the less attractive individual optimally engages in.

Thus, G&S’s ideas may be reconciled with those of Trivers and

others in that the overall optimum still tends toward a higher pro-

portion of short-term tactics for attractive males. The authors’

point is just that less attractive males’ possibilities are constrained

to make more long-term mating optimal.

Abstract: Human mating strategies are contingent on individual

prospects. Gangestad & Simpson provide a useful framework to explore

these differing prospects, but do not take sufficient account of what is

known ethnographically about mating decisions. Women often do not se-

lect their own long term mates. Men often have two or more long term

mates, and can invest in the offspring of short term matings also.

Gangestad & Simpson’s (G&S’s) insistence that there is not one

best male and one best female mating strategy in human beings,

but instead a range of optimal strategies, contingent on individual

characteristics and on the natural and social environment, is im-

portant and timely. However, although this sophisticated target ar-

ticle organizes a large number of data from several domains, there

remain other domains whose findings are relevant to its model

that “suggests that women should vary in their ‘exchange rate’ be-

tween a partner’s genetic fitness (indexed by FA [fluctuating asym-

metry]) and his investment, whereas men should vary in their

‘exchange rate’ between short-term mating effort and long-term

parental investment” (sect. 5.5, first sentence). I concentrate here

on two ethnographic considerations pertinent to the model, and

particularly to its assumptions (1) that a woman’s choices govern

A similar analysis would apply to females. If the possibilities

shown in Figure 1 were for two females, particularly human fe-

males, they might tell a qualitatively similar story to that for males.

If two females behaved optimally, the more attractive female

might attain higher reproductive success in a certain environment

(

say, a parasite-ridden environment) than a less attractive female

and might attain that success at a lower proportion of long-term

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Commentary/Gangestad & Simpson: Evolution and human mating

who her long term mate will be; and (2) that a man is either a long

most of the time. A woman does not choose between one long-

term and one or more short-term mates; she has a husband and

chooses among potential lovers. A man does not decide whether

to be a long-term or a short-term strategist; he has a wife or wives

and decides how much effort to put into courting additional

(mainly married) women.

term investor in a single woman and her children or a short term

mate of many women, and that these strategies are mutually ex-

clusive. The ethnographic findings are: (1) that humans do not

only mate; they marry; and (2) that there is a complicated rela-

tionship between long term and short term mating tactics, partic-

ularly for men, rather than a strict tradeoff.

Among the Bari of Venezuela (where, in general, a woman

chooses her husband subject to a veto by her parents) most mar-

ried women take lovers around the time of at least one of their

pregnancies (Beckerman et al. 1998). These lovers are acknowl-

edged as secondary fathers of the children born of those preg-

nancies and are supposed to give them fish and game. Children

with secondary fathers have higher survivorship to age 15 than

children with only a single father. In field interviews, older Bari

women repeatedly volunteered that in traditional times “the girls

always fell in love with the best hunters.” They were speaking of

both husbands and lovers. The two points here are that being a

good hunter (almost certainly an indication of superior health, sta-

mina, and sensory acuity) was a trait desired in both long- and

short-term mates; and that in this case the short-term mates also

often supplied resources. This situation appears to have been

rather common among lowland South American peoples. In such

cases, men who were secondary fathers for other men’s wives’ chil-

dren did not usually give up their long term investment in their

own wives and primary children.

1

. Marriage: With one possible exception (Cai 1997), all known

human societies have the institution of marriage. There is every

reason to believe that it is a very old custom, relevant to our evo-

lution. In all but a few ethnographically famous but statistically

unimportant cases, this institution links one or more men with one

or more women in a socially sanctioned relationship that includes

rights of sexual access and some obligations of support for the chil-

dren born to the marriage. The importance of this support is cul-

turally variable.

The greatest difficulty for the G&S thesis relating male FA to

female mate preference is that in many, probably most tribal so-

cieties – those societies most similar to the social EEA in which

our mating preferences evolved – ethnographers repeatedly

record that women alone do not choose their husbands. Their par-

ents choose for them to a greater or a lesser degree. Although it

would probably be possible to construct a scale ranging from com-

plete parental control of marriage choices to complete autonomy

of the marrying woman, and to locate a large number of tribal so-

cieties along this continuum, that useful task remains to be done.

If it were done we could begin to ask which circumstances lead to

parental control and which to bridal autonomy. What we do know

now is that the selection of the husband, the long term mate who

has primary responsibility for provisioning the children (except in

some matrilineal, matrilocal societies, where that responsibility

may fall primarily on the woman’s father and brothers) is often

made without regard to the woman’s perception of the desirabil-

ity of her new husband, or at least without primary regard for her

opinion.

Although clearly there must be limiting conditions where so

much time, effort and resources goes into short-term mating that

nothing is left over for long-term investment, and vice versa, the

more common situation may be the one sketched here, in which

well favored men pursue both strategies successfully. One would ex-

pect that this dual strategy would become even more common in

the presence of resources that can be accumulated and inherited.

To my knowledge, no one has yet attempted a study of the pref-

erences of the parents of nubile women for the long term mates

of their daughters with respect to FA, but such a study is clearly

called for. Because tribal parents typically have several children to

marry off, and because a marriage is usually a political event, with

each marriage altering the marital possibilities of the unmarried

siblings of the bride, it is not clear that a woman’s parents, maxi-

mizing their fitness summed over all their offspring, would opti-

mally have the same preferences as any individual daughter, even

if they attended to all the same cues.

There is an additional attribute of marriage underdeveloped by

G&S. The majority of societies regard polygyny (multiple wives)

as the ideal form of marriage. Most men never achieve it, but the

major mating strategy tradeoff in polygynous societies is not be-

tween a “single, exclusive long-term relationship” (sect. 5) with

substantial paternal investment and many short term matings with

little or no investment; but rather between a single long-term re-

lationship with substantial paternal investment and two or more

such relationships.

Fixed versus flexible strategists: Individual

differences in facultative responsiveness?

Jay Belsky

Department of Psychology, Birkbeck College, University of London, London

WC1E 7HX, United Kingdom. j.belsky@psychology.bbk.ac.uk

Abstract: Gangestad & Simpson’s central premise regarding individual

differences is applied to their facultative-argument based on mating-

strategy, for individual differences in susceptibility to contextual effects.

Some individuals may be relatively fixed strategists who are rather unre-

sponsive to context when it comes to mating, whereas others, perhaps

most, may be, as G&S propose, flexible strategists.

Individual differences in mating, like so much other behavior,

most certainly exist, as Gangestad & Simpson (G&S) convincingly

argue in their target article. But perhaps the implications of the

ubiquity of individual differences in general have not been suffi-

ciently considered in their target article. That is, although G&S

make a compelling case for the contingent nature of mating be-

havior with respect to both males and females, they seem to have

failed to entertain the possibility of individual differences in sus-

ceptibility to the very conditional effects around which they base

their argument. In advancing this proposition, it is my intent not

so much to criticize G&S as stand on their shoulders to extend

their insightful analysis.

On average, it may make good evolutionary and biological sense

for males and females to respond facultatively to variation in mat-

ing context, but such an average effect could mask underlying vari-

ation in responsiveness to contextual conditions, a possibility that

goes unmentioned in G&S’s otherwise thoughtful target article. In

advancing this proposition, I mean to apply to their analysis the

very argument which G&S used to appreciatively critique existing

models of mating. That is, just because there exist mean differ-

ences in mating strategies across contexts, it does not follow that

To put it baldly, the presumption that matings with multiple

women exclude long-term relationships with substantial invest-

ment in both the women and the children is inadequate – as is the

idea that a man’s investment in his children is a simple reflection

of the exclusivity of his “investment” in his relationship with his

wife. The Relationship-Specific Investment Inventory is a catalog

of contemporary American middle class fashions in “relationship

counseling” that does not speak to the question of men’s invest-

ment in children, even in our own culture.

2

. Relationship between long term and short term matings: In

general in the tribal world, long-term mates are husbands and

short-term mates are lovers. Although a woman’s parents often

choose her husband, the woman herself, with only sporadic ex-

ceptions, chooses her lovers. It is an important difference. It is also

important to recognize that in the great majority of tribal societies,

the great majority of fertile women and mature men are married

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Commentary/Gangestad & Simpson: Evolution and human mating

there is no variation in the degree to which individuals prove re-

sponsive to contextual conditions.

tremely healthy and beautiful women, fixed rather than flexible

mating tactics should have evolved. It is accordingly useful to con-

sider for whom the flexibility would, on average, have been more

expensive reproductively, in addition to the average benefits of

flexible mating behavior.

It could be useful to think in terms of fixed and flexible strate-

gists or, at least, in terms of variation in flexibility of strategy.

Whereas some males or females, perhaps even most, may inherit

the capacity to adjust their mating strategy flexibly, in line with

G&S’s analysis, others may have inherited a far less flexible and

more fixed mating strategy. It may be problematic to assume, as

G&S implicitly appear to do, that all males and females are flexi-

ble strategists, or at least equally flexible strategists in the domain

of mating. As I have argued elsewhere with respect to the effects

of rearing on infant-mother attachment security (Belsky 1997b),

early problem behavior (Belsky et al. 1998), and mating and par-

enting in adulthood (Belsky 1997a), it might be useful to think in

terms of variation in susceptibility to contextual effects in the case

of facultative mating strategies. Thus, some individuals may be

less facultatively responsive than others – and for just the same

reason that G&S argue in favor of facultative responsiveness in

general – namely, reproductive fitness.

Individual differences in evolutionary

perspective:The games people play

a

b

Diane S. Berry and Stan A. Kuczaj

a

Department of Psychology, Southern Methodist University, Dallas, TX

7

5275-0442; dberry@mail.smu.edu; ^bDepartment of Psychology, University

of Southern Mississippi, Hattiesburg, MS 394-6-5025.

skuczaj@ocean.otr.usm.edu

Abstract: The emphasis on individual differences in evolutionary theories

is important and has not received adequate attention. Strategic Pluralism

makes a major contribution by addressing these issues, but like other evo-

lutionary models (e.g., game theory) does not articulate the specific mech-

anisms underlying strategy selection. Specification of such mechanisms is

an essential next step in the development of these models.

I take no issue with the notion that mating strategy should vary

with contextual conditions, whether those conditions be defined

in terms of men’s genetic quality or capacity for long-term parental

investment in the case of women or, in the case of men, in terms

of women’s long- or short-term mating strategy. But it would seem

that in some cases at least, reproductive payoffs would be greater

Gangestad & Simpson’s (G&S’s) Strategic Pluralism model pro-

vides a thoughtful account of individual differences from an evo-

lutionary perspective. As argued elsewhere, the assumption that

evolutionary approaches predict strict universals in preferences

and behaviors is simplistic and at odds with the well-documented

variability in human behavior (Berry 2000; Buss & Greiling 1999).

The target article provides a sophisticated account of individual

differences via the concept of evolved conditional adaptations –

evolved preferences that shift as a function of characteristics of the

environment. For example, G&S note that highly attractive men

are more successful in short-term mating contexts than are less at-

tractive men. Men’s conditional adaptations, they argue, therefore

alter their preferences and behaviors as a function of their own at-

tractiveness. Highly attractive men put relatively more effort into

short-term mating, whereas less attractive men devote relatively

more effort to long-term strategies. Such “conditional strategies”

seem likely to produce individual differences in human behavior.

What exactly is a conditional strategy? If such strategies reflect

conscious decisions that individuals make to enhance reproduc-

tive success, a more complete understanding of these strategies

will depend on a clearer picture of the evolution of human cogni-

tion. However, if such strategies are not conscious choices, they

are reminiscent of explanations of nonhuman animal mating

strategies based on game theory (Dawkins 1980; Maynard Smith

1974). These explanations assume an individual’s reproductive

success depends on the behaviors of other members of the popu-

lation. For the example of male attractiveness considered here,

game theory might assume that all males are predisposed to seek

short-term mating strategies, but only attractive males will suc-

ceed with this strategy. Attractive males succeed with this ap-

proach because women are more likely to seek short-term mating

situations with attractive men. After all, if women did not also en-

gage in short-term matings, men should have evolved strategies

that would procure the best long-term mates, regardless of

whether the men are attractive or not. Thus, the strategies that

men evolved were undoubtedly influenced by the strategies that

evolved in women (and vice versa). Given a short-term strategy is

less likely to work for unattractive males, they adopt a long-term

strategy that is more likely to produce successful results. Game

theory supposes that these conditional strategies are inherited

programs that influence mating behavior by providing alternative

strategies for different situations. Alternative strategies allow less

fit individuals (in our case, less attractive males) to increase their

chances of reproductive success.

(

on average) across generations when particular individuals stick

to a single, inflexible (or relatively inflexible) strategy. Consider in

this regard the male who inherits the very developmental stability

that G&S argue is central to female mating strategy. Were highly

stable males who were heritably resistant to environmental threats

to their low fluctuating asymmetry genetically committed to a

short-term mating strategy, it is not difficult to envision that across

generations such fixed strategists would experience greater re-

productive success than if they varied their mating tactics in ac-

cord with contextual conditions. Although there certainly would

have been times when such a fixed strategy did not pay off, those

may be the exceptions rather than the rule. In the case of some

men, behaving facultatively would not have been adaptive on av-

erage, and so for men with the genes in question, a fixed rather

than flexible strategy would be persistently practiced. In other

words, evolution may have maintained in the gene pool, genes that

promote fixed – or relatively fixed – as well as flexible mating

strategies.

Can a similar argument be advanced in the case of women? It

is certainly not difficult to imagine that a female of high mate value

due principally to genetic factors could also have inherited genes

that reduced her facultative responsiveness to mating conditions

because across time the payoff of a fixed (long-term) mating strat-

egy may have been so great as to outweigh the rare, periodic gain

achieved by varying such usually sound mating tactics. Indeed, at-

tractive healthy women might have been so assured of securing

high value mates across human evolutionary history that the rare

costs associated with not engaging in short-term mating under

propitious conditions would not outweigh the much larger and

highly reliable (even if not perfect) gain from always seeking long-

term investment. Were that the case, one might again expect

genes that fostered fixed mating strategies as well as facultative

ones.

To summarize, in the same way that mean differences in male-

female mating strategies most assuredly mask the within-gender

variation that, as Gangestad & Simpson compellingly argue, has

evolved due to its adaptive value, mean male and female differ-

ences in mating behavior across context may mask variation in the

degree to which both males and females show facultative respon-

siveness to mating conditions. In the case of some and probably

most males and females, facultative responsiveness makes great

evolutionary sense. But in the case of others, a fixed or at least less

flexible strategy may be the order of the day, week, life, and even

lineage. When average reproductive payoffs for flexibility were

less, as they may have been for extremely symmetrical men or ex-

G&S’s model is similar to game theory explanations of mating

behavior in another respect. Neither theory adequately specifies

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the nature of the underlying mechanisms involved in strategy se-

A comprehensive theory of human mating

must explain between-sex and within-sex

differences in mating strategies

lection. The concept of conditional adaptation could benefit from

greater attention to the underlying mechanisms that evaluate

characteristics of the environment and shift a person’s desires and

preferences as a function of those characteristics. G&S do not fully

articulate how contextual factors produce these shifts in mating

strategies. One might argue that until intervening processes are

proposed and described in deeper detail, the term “conditional

strategy” is reduced to a description of behavior, rather than an ex-

planatory concept. We hasten to add that most discussions of evo-

lutionary bases of human behavior – including our own (Berry

April L. Bleske and David M. Buss

Department of Psychology, University of Texas, Austin, TX 78712;

bleske@mail.utexas.edu

Abstract: Gangestad & Simpson make a major contribution by highlight-

ing the importance of mate choice for good genes, the costs of alternative

strategies, and tradeoffs inherent in human mating. By downplaying sex

differences and ignoring the nongenetic adaptive benefits of short term

mating, however, they undermine their goal of “strategic pluralism” by

presenting a theory devoid of many documented complexities of human

mating.

2

000; Kuczaj 1998) – have been vague about underlying mecha-

nisms. The field of evolutionary psychology could benefit greatly

from more attention to this issue.

How might a man’s attractiveness as a mate become linked with

his preferred mating strategy? If attractive men can increase re-

productive success via short-term strategies, and less attractive

men attain the greatest reproductive success via long-term strate-

gies, one possibility is that selection yielded two types of men:

Attractive men who prefer short-term approaches, and unattrac-

tive men who prefer long-term strategies. (This is analogous to

Gangestad & Simpson’s [1990] proposed explanation of individual

differences in female sociosexuality.) If we assume that attractive-

ness, fitness, and strategies are inherited in such a way that at-

tractive men possess one strategy and unattractive men another

We concur with Gangestad & Simpson’s (G&S’s) central claims

that good genes are important in human mate selection and that

there are tradeoffs in human mating – ideas present in prior the-

ories of human mating, although not as explicitly as they deserve

to be. Their work on fluctuating asymmetry is innovative and

makes a substantial contribution to knowledge.

Despite our admiration for their work, we found several prob-

lems with their current formulation – their distorted presentation

of Sexual Strategies Theory (SST), their treatment of sex differ-

ences in human mating strategies, and their neglect of potential

nongenetic adaptive benefits of short-term mating.

Sexual strategies theory. In setting up the foundation and back-

ground for their own formulation, G&S appear to downplay the

widely documented sex differences in human mating. They do this

in part by presenting a distorted and selective depiction of SST

(Buss 1994b; 2000; Buss & Schmitt 1993), using a double standard

when comparing sex differences to within-sex effects, and failing

to acknowledge explicitly the profoundly sex-differentiated nature

of their own proposal.

Although G&S occasionally insert a qualifier, most readers will

come away from their article believing that SST is all about men

pursuing short-term and women pursuing long-term mating strate-

gies. In contrast, SST proposes that both men and women have

evolved a complex menu of mating strategies, including both short-

term and long-term strategies, and that the combination each in-

dividual selects from this menu depends on a variety of contexts,

such as operational sex ratio, mate value, physical attractiveness,

quality of available alternatives, parental and kin influences, local

cultural norms, reputational consequences, and many others (Buss

1994b; 2000; Buss & Schmitt 1993; Greiling & Buss, in press).

G&S’s version of “strategic pluralism,” as we elaborate below, turns

out to be considerably narrower than that of SST.

Double standard of evaluating results. To set the stage for

their theory, G&S attempt to minimize the existence of empirical

findings of sex differences. They do this by converting effect sizes

into indices of explained variance. To take one concrete example,

Buss and Schmitt (1993) found an effect size of 1.00 for sex dif-

ferences in how much time would elapse before seeking sexual in-

tercourse. Men and women differ by a full standard deviation,

which greatly exceeds the magnitude of the vast majority of the

“strongest” findings in psychology. In an apparent effort to dimin-

ish the importance of sex differences, G&S translate the effect size

into a percentage of variance accounted for of 20%. When it

comes to their own key findings, however, they choose to report

correlations instead, and fail to report the percentage of variance

accounted for. For one of their key theoretically predicted find-

ings – the link between FA and attractiveness – they report a mean

correlation across studies of Ϫ.20. This translates into merely 4%

of the variance accounted for! A key sex difference that the au-

thors take pains to minimize, in other words, accounts for five

times more variance than does an effect that appears to be a the-

oretical lynchpin of their theory. We find this “double standard,”

using one set of statistical indicators for findings they try to down-

play and a different set for their own preferred findings, to be of

(

and this is, of course, a big assumption), then evolution has pro-

duced individual differences in men’s mating preferences that are

linked to their attractiveness. However, note that this really is not

an example of a conditional adaptation – a single adaptation that

produces different preferences as a function of other variables. In-

stead, this explanation posits the evolution of different adaptations

in different individuals. The mechanism of strategy choice in such

a case is genetic, with one’s attractiveness being paired with a strat-

egy that optimizes mating success for one’s appearance. Strategy

choice, then, is neither conscious nor a function of the environ-

ment, but instead genetically determined.

There are, of course, alternative possibilities. Perhaps all men

desire many low-investment sexual partners. However, attractive

men typically attract such partners, whereas unattractive men

rarely do. Thus, attractive men are likely to succeed via this strat-

egy, but unattractive men are not. If unattractive men can suc-

cessfully secure one sexual partner by adopting a long-term strat-

egy, and they adopt such an approach, they will have at least one

partner. In contrast, if unattractive males adopt a short-term ap-

proach, they are more likely to have no partners (unless, perhaps,

there are no attractive males available). Thus, in this scenario, un-

attractive men adopt a long-term strategy not because they prefer

one partner to many, but because one is better than none. This ex-

planation predicts a pattern of behavior identical to what has been

documented empirically. However, it does not describe a condi-

tional adaptation as described by G&S, who posit actual differ-

ences in preferences as a function of a man’s attractiveness. In-

stead, this is an example of a single sex-typical evolved preference

–

a desire for many partners – the realization of which is con-

strained by women’s reactions to a man’s attractiveness, and is

more consistent with the notion of conditional strategies in game

theory.

As this brief description illustrates, it is difficult to specify the

underlying processes that are involved in strategy selection. How-

ever, continued efforts to do so are imperative if we are to move

from describing behaviors to explaining them.

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dubious merit for the goal of a balanced portrayal of the empiri-

cal evidence.

One means by which trade-offs between short- and long-term

matings may be guided is through individual differences in the

relative reinforcement value of a greater long-term frequency of

intercourse (FSI; reportedly most easily obtained through rela-

tively long-term cohabitation; Brody 1997) versus an accumula-

tion of a greater lifetime number of sexual partners (LNSP)

through a series of short-term matings. Mixed strategies are not

uncommon, but for the purposes of this exposition the LNSP and

FSI focussed approaches will be contrasted. Although FSI and

LNSP were correlated in some studies (especially those using

young samples in which age at first intercourse is an important

factor), they have stronger associations with separate clusters of

variables. LNSP is associated with novelty seeking, habituation or

boredom proneness, and impulsiveness. FSI is associated with

measures of physical sensitivity (consistent with a simple operant

model of greater frequency of enjoyed activities), pairbonding,

health, consistency of female orgasm, and hormonal/autonomic

factors (reviewed in Brody 1997). Another factor is the individual

relative appeal (or aversiveness) of the intimacy or social propri-

ety associated with longer-term relationships. Thus, individual

differences in personality and related psychophysiology may af-

fect the relative behavioral reward of LNSP and FSI focussed

strategies.

Within-sex and between-sex differences. Perhaps more im-

portant, it is not necessary to minimize the existence of well doc-

umented sex differences in human mating to highlight the impor-

tance of within-sex variation. Both can be, and are, important.

Men have roughly ten times the circulating testosterone as

women, for example, but within-sex variation in testosterone is

large and covaries with an important suite of psychological vari-

ables within each sex (Mazur & Booth 1998). Similarly, men and

women differ profoundly in certain mate preferences and in their

desires for partner variety, yet there are also substantial within-sex

variations in these qualities. It is not necessary to downplay one in

order to make an argument for the other.

Minimizing sex differences may play well to a politically cor-

rect crowd, but G&S’s own proposed theory is in fact highly sex-

differentiated. In essence, they propose that women seeking

short-term mating pursue men with good genes, whereas men

seeking short-term mating are going for increased opportunities

to inseminate a variety of women. They further propose that

women seeking long-term mating pursue men who will provide

parental care, whereas men seeking long-term mating are por-

trayed as “genetic losers” who lack the genetic fitness to succeed

in short-term mating (we concur with the former, but not the lat-

ter, contention). Eliding over these and other stark sex differences

contained in their own theory may make it more palatable for

some, but there is no getting around the fact that one cornerstone

of their theory involves sex differences.

Women’s short-term mating. Although G&S present their the-

ory as one of “strategic pluralism,” we find their proposal to be nar-

rower or less pluralistic than is warranted. While focusing exclu-

sively on the “genetic” benefits to women of short-term mating,

they effectively ignore a host of other plausible hypotheses about

the adaptive benefits to women. Studies of women’s desires in

short-term mating, women’s perceptions of the benefits of short-

term mating, and the contexts in which women pursue short-term

mating lend plausibility to several hypothesized functions: to ac-

quire immediate economic benefits, enact mate switching, culti-

vate a potential back-up (“mate insurance”), or to evaluate poten-

tial long-term mates (Buss 2000; Greiling & Buss, in press). These

studies, of course, are limited in a variety of ways and are by no

means definitive. Nonetheless, we believe that a comprehensive

theory of strategic pluralism must include these neglected com-

ponents of women’s short-term sexual strategies rather than focus

narrowly on genetic benefits.

Conclusion. In sum, a theory that accounts for within-sex vari-

ation need not, and cannot, ignore the large and well-documented

sex differences in sexual strategies. It must explicitly acknowledge

the sex-differentiated functions of short-term and long-term mat-

ing contained in the theory. And it should not focus narrowly on

good-genes benefits to the exclusion of a range of other plausible

functions of short-term mating.

Gangestad & Simpson (G&S) found that women in their sam-

ples were more likely to report desiring men with low fluctuating

asymmetry, and that those men were characterised by being more

muscular, violent (and given the results of the Gangestad &

Thornhill 1998b study, perhaps more redolent). One might con-

jecture that those women who are more attracted to pairings with

such men might be less sensitive or cultivated (or more attuned to

the dramatic and impulsive) and less inclined to the long-term FSI

approach. Given that women who use oral contraception have

greater mean FSI than those who do not, excluding pill users from

Gangestad and Thornhill’s (1998b) study of women’s olfactory ap-

praisal of the shirts of men of varying fluctuating asymmetry

(though understandable given the endocrinologic variables that

were utilized) may have biased the sample toward those women

more inclined to a short-term relationship niche.

The one published study cited by G&S examining the relation-

ship between sexual reward (orgasm) and fluctuating asymmetry

(Thornhill et al. 1995) also gives rise to methodological concerns.

The possibility of a bias in the direction of over-reporting (rather

than actually experiencing) a greater rate of orgasm by the women

with more symmetrical (more violent) partners must be consid-

ered, especially given that the correlation between partners re-

ported FSI was quite modest. However, it is also possible a greater

FSI (as noted above, FSI is associated with greater female orgasm

consistency, at least in nonprostitute women) is experienced by

women with more aggressive partners. Apt and Hurlbert (1993)

found that abusive relationships involved a greater FSI than con-

trols, an exception to the general association of greater FSI with

better partnership (Brody 1997).

G&S posit that environments with a high level of pathogens

may increase the drive to seek indicators of good genes and also

encourage short-term mating strategies, whereas venues with low

levels of pathogens favor long-term mating. When environments

are compared at an international level, FSI is associated with life

expectancy (r ϭ .61), per capita gross domestic product (r ϭ .83),

and an index of political freedom (r ϭ .75; all p Ͻ .01; Brody

The trade-off between frequency of

intercourse and sexual partner accumulation

may reflect evolutionary adaptations

1

997). At least life expectancy is inversely related to pathogen

Stuart Brody and Caterina Breitenstein

Center for Psychobiological and Psychosomatic Research, University of Trier,

prevalence (perhaps the pathogenic influences of a repressive

regime or barren economy should be considered in addition to

threats posed by microorganisms). There are many possible ex-

planations for such correlations (such as the same strengths that

make for superior technological development also facilitate a

more enduring sexuality). However, the associations between

FSI and measures of a less threatening environment are largely

consistent with FSI being a proximal influence on the trade-

offs predicted by the Sexual Strategies Theory of Gangestad &

Simpson.

54290 Trier, Germany. brody@fpp.uni-trier.de

members.xoom.com/stuartbrody

Abstract: The adaptive trade-offs between long- and short-term matings

may be mediated or at least reflected partially by the trade-offs between

the relative reinforcement obtained through a greater frequency of inter-

course (typically greater among cohabitants) versus a greater frequency of

partner change. The differing correlates of each approach and meshing

with the Sexual Strategies Theory of Gangestad & Simpson are discussed.

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Commentary/Gangestad & Simpson: Evolution and human mating

Eating their cake and having it too: Or, how

women maximize reproductive success by

simultaneous mating and dating

But if that is the case, then the strategy is no longer conditional in

the sense that G&S mean it, any more than we would say that my

breathing is conditional on the environment’s providing air. If

pathogens are always in the environment, the women should al-

ways be seeking good-gene matings. The same goes if pathogene

presence is a fluctuating but recurring phenomenon. In this case

also, women should be trying to mate with good-gene males

throughout their reproductive lives.

Gwen J. Broude

Department of Psychology, Vassar College, Poughkeepsie, NY 12604-0152.

broude@vassar.edu

Abstract: Data support the claim from the target article that women, both

cross-culturally and historically, have employed a variety of mating strate-

gies, marrying but also engaging in short-term unions. But those strategies

appear to be practiced simultaneously and not conditionally as Gangestad

The idea that women practice conditional mating strategies is

also challenged by the data. The fact is that, cross-culturally and

historically, virtually all women marry. Contemporary society is

anomalous in this regard. Further, in a world-wide sample of 69

cultures, the mean age of marriage for females is 16.29 years (un-

published codes, Palfrey House, Harvard University). Long-term

mating does not look like a conditional strategy. Rather, it looks

like a universally practiced adaptation. But so are women engag-

ing in short-term matings. As I have indicated, extramarital sex on

the part of wives is common across cultures, in spite of the poten-

tial repercussions. Indeed, while G&S speculate that women

might forego extra-mate pairings except as a conditional strategy

because they fear risking disruption of the long-term pair bond

with their husbands, wives across cultures appear to be willing to

take the risk. This is reflected in the absence of a significant asso-

ciation between punishments for extramarital sex across cultures

and actual incidences of extramarital sexual activity (Broude

1980).

The data, in short, are not consistent with the idea that women

are adopting conditional mating strategies. Rather, it appears that

they engage in a variety of mating strategies simultaneously.

Across time and place, women tend to marry and have short-term

affairs at the same time. This makes good sense from the per-

spective of evolutionary theory. Women benefit from the invest-

ment of a long-term mate but, because of the limitations on their

reproductive capacity, cannot wait forever to attract G&S’s proto-

typic good-gene male as a husband. Rather, they compromise and

marry what is available. But a woman with an investing husband

at home as her insurance policy can seek out short-term matings

with a good-gene male. Thus, women seem to engage in mating

strategies that allow them to eat their cake and have it too.

&

Simpson propose, a finding consistent with assumed constraints on the

potential reproductive success of females.

In their target article, Gangestad & Simpson (G&S) review a set

of by now well publicized findings to the effect that both males

and females are attracted to members of the opposite sex who dis-

play body symmetry. What is new here is the additional idea that

men and women practice mixed or conditional mating tactics tai-

lored to specific environmental circumstances. The key prediction

is that females will shift from long-term to short-term mating tac-

tics when environmental circumstances, especially the prevalence

of pathogens, place a premium on the good genes (correlated with

body symmetry) of the partner. In fact, both theory and data do

support the general idea that women employ a variety of mating

strategies and probably did so in our environment of evolutionary

adaptedness (EEA). I wish to argue, however, that those strategies

are not likely to be conditional in the way that G&S suppose.

The claim that females adopt a number of mating tactics is sup-

ported by the fact that, across time and place, women have mar-

ried but also engaged in premarital and extramarital sex. Premar-

ital sex is uncommon in only 20% of 113 cultures from the

Standard Cross-Cultural Sample and extramarital sex is uncom-

mon in only 28% of 52 Standard Sample cultures (Broude &

Greene 1976). Buss (1999) reports that between 20% and 50% of

women engage in extramarital affairs in the United States, and

conservative estimates based on measures of genetic relatedness

indicate that 10% of children are fathered by someone other than

the mother’s husband (Allman 1994). Indeed, short-term sexual

activity on the part of females is a logical requirement of standard

sexual selection theory. If males promote their fitness by engaging

in short-term mating, then women must be engaging in the same

kind of activity. Otherwise, with whom are the males mating? Fur-

ther, human beings exhibit a variety of physiological characteris-

tics viewed as consistent with the idea that neither men nor

women are or have in the past been exclusively monogamous.

Both long-term and short-term mating, then, do appear on the-

oretical and empirical grounds to be female mating strategies. It

is the idea that these are conditional mating strategies that I wish

to question. Partly, the theory seems to me to be implausible on

sheerly logical grounds. G&S are arguing that women make deci-

sions about mating strategies on the basis of environmental cues.

The strategy of engaging in short-term matings should kick in

when the environment favors mating with men with good genes.

The primary environmental cue that G&S emphasize is the preva-

lence of pathogens. The idea that behavior is triggered by envi-

ronmental circumstances is entirely reasonable and has gained

considerable currency since Barkow et al. (1992) introduced the

notion of Darwinian algorithms into the evolutionary psychologi-

cal literature. But how would seeking out a male with good genes

count as a good mating strategy when pathogens are prevalent?

Here is the problem: pathogen prevalence could, theoretically, be

a one-shot short-term, a long-term, or a recurring environmental

challenge. If pathogen prevalence is a one-shot short-term event,

then the fitness-enhancing trait of disease resistance passed on to

a woman’s offspring will become obsolete, perhaps even by the

time the baby is born if the pathogen threat is sufficiently tran-

sient. Short-term mating strategies in which women are choosing

good-gene men, then, are only likely to promote inclusive fitness

if pathogen prevalence is a chronic problem in the environment.

Scientific truth and perceived truth

about sexual human nature:

Implications for therapists

Joseph A. Buckhalt and Erica J. Gannon

Department of Counseling and Counseling Psychology, Auburn University,

Auburn, AL 36849. buckhja@mail.auburn.edu

www.auburn.edu/~buckhja

Abstract: Therapists and their patients must deal with the negative se-

quelae of short term mating strategies. Implications for therapy of Ganges-

tad & Simpson’s strategic pluralism theory are compared with those of

Buss’s sexual strategies theory and Eagly’s social role theory. Naive theo-

ries held by therapists and patients, as well as prevailing societal views, are

posited as influential in determining the course and outcome of therapy.

John McPhee, in his collection of essays The control of nature

(1990), provides several descriptions of attempts by civil engineers

to control the physical environment; his documentation of the

fragility of our successes is humbling. Although much of govern-

ment, law, religion, and more recently, psychotherapy, is con-

cerned with influencing human nature, including its sexual as-

pects, social engineers have arguably fared worse than have civil

engineers.

Therapists are among the many who deal daily with the nega-

tive sequelae often associated with short-term mating strategies,

including the birth of unwanted children, abortion, sexually trans-

mitted diseases, rape, murder, and divorce. For many countries in

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595

Commentary/Gangestad & Simpson: Evolution and human mating

Western societies, the dominant paradigm for understanding and

controlling human sexuality derived from religion. Humans were

assumed to have a base nature, and only through the socialization

of religion could any semblance of order be maintained. In some

contemporary cultures, this paradigm continues to guide attempts

to control sexual behavior. In other cultures, religion-based con-

trol systems have been supplanted by secular legal, educational,

medical, and psychological systems, all of which are fed by the the-

ories and data of science.

From our perspective as professional applied psychologists, we

are concerned with how alternative scientific theories may be use-

ful in understanding sexual behavior, especially the kinds of be-

haviors that lead to negative consequences, and further, how ther-

apeutic efforts may be affected. Gangestad & Simpson’s (G&S’s)

account of how sexual strategies may have evolved is framed pri-

marily as a modification and extension of Buss and Schmidt’s

Putting people before parasites and places

Anne Campbell

Department of Psychology, Durham University, Science Laboratories,

Durham DH1 3LE, England. a.c.campbell@durham.ac.uk

Abstract: The strategic pluralism model depends upon pathogen preva-

lence and environmental hardship being independent. Evidence is pre-

sented that they are positively correlated. The rise in short-term mating

strategy in the United States is better explained by changes in the opera-

tional sex ratio than by increases in pathogen prevalence. Nonetheless, in

highlighting the advantages of a high-investment strategy to less attractive

males, Gangestad & Simpson’s model helps to clarify the dynamics of

frequency-dependent selection.

According to Gangestad & Simpson (G&S), variability in female

mating strategies derives from women’s different responses to

pathogen prevalence and harsh environmental conditions. The re-

lationship between the two is critical both theoretically and em-

pirically.

(

1993) Sexual Strategies Theory (SST) and both contrast with so-

cialization theories such as Eagly’s (Eagly 1987; Eagly & Wood

999), who proposes that culture is largely responsible for the dif-

1

ferences in how males and females act with regard to mating.

As therapists, we are often not as concerned with the actual

mechanisms supporting sexual behavior, but how patients and

therapists construe the causes of their behaviors. As Heider

Before addressing this, it is necessary to clarify the meaning of

harsh environments. Gangestad & Simpson define them tauto-

logically as “environments in which biparental care and stable

pair-bonds are needed and expected” (sect. 5.7.1). Effectively,

however, they treat them as characterised by resource scarcity

where “women could not provide for all the nutritional needs of

their offspring” (sect. 5.6.2). Such harsh environments also incite

competition for scarce resources (Clutton-Brock 1991, p. 257)

leading to high crime rates and other forms of social pathology

which exacerbate environmental challenges.

If parasites and harsh environment are negatively correlated

across geographical sites, then one female strategy would be uni-

versal since women everywhere would benefit from making the

same choice. If they are negatively correlated within a geograph-

ical site, for example, as a function of social class, then women of

the same class should all select the same strategy. If they are pos-

itively correlated (either between or within ecological niches), the

distinction between them evaporates and there is no possibility of

making differential predictions. Unless niche-independent ge-

netic differences in strategy choice are invoked, the viability of the

theory depends upon a near zero correlation between environ-

mental harshness and pathogen prevalence.

From an empirical viewpoint, there is much evidence that the

two are positively correlated and associated with poverty. Across

and within nations, indicators of parasite prevalence (infant mor-

tality rate, probability of dying before their fifth birthday, the

percentage of infants immunised, mortality from diarrhoeal and

respiratory infections, malaria, measles, tuberculosis) and harsh

environment (gross domestic product, death from accidental

causes, life expectancy, percentage of poor, national health ex-

penditure as a proportion of GNP, proportion of children whose

weight-for-age is acceptable by international standards) go hand

in hand (World Health Organisation 1999).

The rate of single-parent families has risen dramatically in

Western countries. In the United States between 1970 and 1990,

premarital births rose from 9% to 22% of births to white women

and from 42% to 70% to African-Americans (Weinraub & Grin-

glas 1995). According to G&S such a rise would be attributed to

higher pathogen prevalence yet this period has seen a rise in im-

munisation programs and in pre- and post-natal care. What has al-

tered in post-war years is the operational sex ratio (Guttentag &

Secord 1983; Pedersen 1991). Changes in attitudes to casual sex,

single parenthood, and divorce are strongly related to the relative

paucity of males, which puts them in a strong market position to

impose their preferred mating strategy. This situation is most

marked in the lowest social classes where the pool of eligible males

is further reduced by male unemployment, drug addiction, and

imprisonment (Campbell 1995). If this argument is correct, then

female mating strategies are frequency dependent and driven by

the availability and preferred strategy of males and females, rather

than by ecological factors in the environment.

(

1958) argued, we are all “naive” psychologists, and our informal

theories may serve to guide (and justify) much of our behavior. A

standard therapeutic assumption drawing from Eagly’s work

might be that sexual behavior is largely learned, responsive to

contemporary social structures, and thus malleable to a great de-

gree. Although the socialization that shapes the sexual behavior

of males and females is extremely powerful, therapists and clients

who view sexual behavior as largely socialized may nevertheless

view aberrant sexual behavior as potentially amenable to treat-

ment. On the other hand, as G&S emphasize, Buss and Schmitt’s

(

1993) SST can lead to the conclusion that “men may have

evolved over human evolutionary history a powerful desire for

sexual access to a large number of women” (Buss & Schmitt 1993,

p. 208). Although SST does acknowledge that both genders

should possess evolved methods for finding long-term mates,

“

men, more than women, are predicted to have evolved a greater

desire for casual sex” (Buss 1999, p. 162). Although Buss (1999)

takes care to note that a characteristic’s arising as a result of evo-

lutionary processes does not preclude that characteristic from

changing within an individual, a belief in SST would lead many

therapists and clients to view sexual desires and sexual behavior

as largely immutable, or at least highly resistant to modification.

If men have “evolved a greater desire for casual sex,” can society

(

or their female partners) blame them if they sometimes act upon

that desire? And are efforts to modify that desire action a waste

of time? G&S seem to offer a synthesis of the “strong nature” po-

sition of Buss and the “strong nurture” position of Eagly, in that

although evolved mechanisms are the primary focus, their mod-

ification of SST does not polarize males and females to a high de-

gree, and there is some recognition that contemporary environ-

mental factors may be responsible for the engagement of ST and

LT strategies in both sexes. As G&S acknowledge, there are many

questions unanswered by the present version of their theory, in-

cluding better specification of conditions that may call forth the

mating logic they propose for each gender. These explications

may eventually yield a theory that better informs the practice of

therapy related to sexual behavior.

For therapy to be effective, considering the naive theories held

by patient and therapist may be as important as knowing what ac-

tual mechanisms are responsible for the troubling behaviors in

question. Concordance of theory between patient and therapist

would seem to be crucial, and the prevailing views of society at

large are also important. Pessimistically enough, for some kinds of

sexual behaviors that concern us, none of this information may re-

sult in therapy being any more effective as a mechanism of pre-

vention or damage control than anything else has been through-

out recorded history.

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Commentary/Gangestad & Simpson: Evolution and human mating

Dawkins (1989) has proposed a mathematical model of this

Current versus future, not genes

versus parenting

process evaluating the pay-off of a successfully-raised offspring

against the costs of wasting time in prolonged courtship and rais-

ing the child. In a monogamous population, men and women do

equally well – they halve the cost of child rearing by sharing it, and

both pay the price of courtship and reap the same reward. If an

unrestricted female comes on the scene, she avoids the price of

courtship but still halves the cost of child-rearing and gains the

reward. But as unrestricted females become more common, the

male’s optimal strategy changes to promiscuity, earning him a

child while paying no cost in waiting or child-rearing. But now the

unrestricted female pays the entire cost of child-rearing alone (al-

though not the costs of delayed mating) leaving her in serious

deficit. A restricted female now starts to do better. Although she

encounters mainly promiscuous males, at least she does not lose

James S. Chisholm and David A. Coall

Department of Anatomy and Human Biology, University of Western Australia,

Nedlands, WA 6907, Australia

{jchisholm; dcoall}@anhb.uwa.edu.au

www.anhb.uwa.edu.au/staff/jchisholm/home/html

Abstract: Gangestad & Simpson’s model of the evolution of within-sex dif-

ferences in reproductive strategies requires a degree of female choice that

probably did not exist because of male coercion. We argue as well that the

tradeoff between current and future reproduction accounts for more of

the within-sex differences in reproductive strategies than the “good-genes-

good parenting” tradeoff they propose.

Gangestad & Simpson’s (G&S’s) model of within-sex differences

in reproductive strategies is based on the widely-accepted deduc-

tive principle and inductive generalization that female mammals

tend to “track” their environments for the resources they require

for parental investment while male mammals “track” females for

–

she will refuse to mate and so will not suffer the costly experi-

ences of her unrestricted rival. As the number of restricted fe-

males rises, promiscuous males will find it harder to find partners

and will accede to monogamy.

1

What this model incorporates, but is ignored by G&S, is the

substantial cost of child-rearing to the woman pursuing a short-

term strategy. For their model to succeed, they must show that a

short-term strategy leads to greater reproductive success than a

long-term strategy despite the doubled cost of child-rearing. But

mortality rates for father-absent children exceed those of two-

parent families (see Geary 1998). Parents in single-parent families

experience greater stress, resulting in reduced parental effective-

ness and poorer child outcomes (Weinraub & Gringlas 1995).

Conditions of poverty, disproportionately experienced by single-

parent families (Hobbs & Lippman 1990), are associated with

child abuse (Pelton 1978; Steinberg et al. 1981).

But the insights afforded by G&S offer a solution to a signifi-

cant problem with Dawkins’ model – the swing back from promis-

cuity to monogamy. Under promiscuity, Dawkins argues, the re-

stricted female does better than her unrestricted competitor

because she does not pay the cost of raising a child alone. True,

but the restricted female also produces no (or very few) offspring

if there are few monogamous males in the population. She wastes

a great deal of time meeting and rejecting promiscuous males and

a women’s reproductive life is a relatively short one. This can

hardly be considered a good outcome from the point of view of in-

clusive fitness. Dawkins glosses over this difficulty and assumes

that eventually monogamous females predominate. Once they do,

he argues, males waste too much time looking for an unrestricted

female and so are forced into monogamy. Although he admits the

time-wasting cost for promiscuous males, he ignores the same cost

for monogamous females – despite female’s shorter reproductive

life. Gangestad & Simpson, however, provide a clear rationale for

why some males should be available to a monogamous female

even when male promiscuity is prevalent. Less symmetrical and

attractive males can maximise their reproductive success by capi-

talising upon a female desire for monogamy. In a previous paper,

Gangestad & Simpson (1990) invoked frequency dependent se-

lection as an explanation of the incontestable flexibility of human

mating strategies. It is a pity that it has all but disappeared from

the present model.

opportunities to mate. It follows, for them, that when female re-

productive success (RS) is determined primarily by resources

available through males, then females are expected to favor males

who are “good parents.” On the other hand, when female RS does

not depend on resources available through males they should fa-

vor males who have “good genes.” Variation in female reproduc-

tive strategies is thus expected to be contingent on the optimal

tradeoff between their capacity to benefit reproductively from

“good genes” versus “good parenting.” Consequently, “men’s ten-

dency to engage in short-term mating should be a direct function

of their genetic fitness (indexed by FA), while men’s propensity to

invest in single, exclusive long-term relationships should be in-

versely related to their genetic fitness” (sect. 5, para. 1). Although

G&S present considerable data that seems consistent with their

model, we feel that the model itself may be flawed and that other

interpretations are possible. We are not convinced that there re-

ally is a tradeoff between “good genes” and “good parenting” or

that it is not subsumed in the already well-known tradeoff be-

tween current and future reproduction.

A major problem for their model is that there is more to sexual

selection than female choice: there is also male coercion (of fe-

males and other males). “Good genes” sexual selection cannot oc-

cur when there is no female choice, and the evidence for female

choice amongst nonhuman primates is weak. Sarah Hrdy even ar-

gues that “there is no evidence from nonhuman primates to indi-

cate . . . ‘female choice for genes’” (1997, p. 16; emphasis added)

and that “male-male competition for rank is more important than

female choice in determining male reproductive success” (ibid.).

Therefore, if hominid females were unable to exert much choice

in sexual matters because of male coercion, then “good genes sex-

ual selection” would not have been very important and we would

not expect “men’s tendency to engage in short-term mating [to] be

a direct function of their genetic fitness.”

On the other hand, female choice was surely a defining feature

2

of the EEA and what drove the evolution of the capacity for con-

tingent differences in male reproductive strategies that we see to-

day. It just wasn’t for “good genes” (as reflected simply in FA, that

is). The evolution of prolonged helplessness in hominid children

opened the way for an alternative male reproductive strategy.

When hominid children evolved the capacity to benefit from more

“

good parenting” than mothers alone could provide, males were

no longer obligated to reproduce exclusively by coercing females

and competing with other males (e.g., Hrdy 1997; 1999; Smuts

1

992; 1995; Smuts & Gubernick 1992). When “good parenting” by

males began to make a difference in female RS, sexual selection

female-female competition) would have favored a greater capac-

(

ity for females to choose mates carefully and wisely. Perhaps this

is why there is more evidence for female choice for “good genes”

in humans than nonhuman primates – if there is. But even if there

is, there is no reason to think that “good genes” wouldn’t also be

involved in “good parenting.” Do “bad genes” cause males to be-

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come “good parents”? Do “good genes” cause males to become

philanderers? If hominid females were increasingly able to choose

males who were “good parents,” and if “good parenting” at least

partly involved “good genes,” then G&S’s distinction between

ories by exaggerating the differences within each sex. Although

their new theory may have certain ideological appeal, we are not

convinced that the differences in sexual desires within each sex are

greater than those between each sex.

“good genes sexual selection” and “good parenting sexual selec-

The claim of greater within sex-variation hinges on the evidence

of “unrestricted” women with what was previously thought to be

“male-like” desires for short-term matings, and “restricted” men

who lack the “powerful desire for sexual access to a large number

of women” previously considered to be universal among human

males. In support of these claims, G&S cite surveys asking such

questions as how many sexual partners individuals expect to have

in the future. From this evidence, they conclude that both males

and females have evolved to pursue both, or perhaps favor either,

long-term and/or short-term mating “tactics” (see Gangestad &

Simpson 1990; Simpson & Gangestad 1991a, for a full review).

There are, however, problems with using this type of evidence to

measure the within and between sex variations in terms of the

evolved desires motivating the sexual behavior.

Short-term matings must be interpreted within the context in

which they occur. This context includes whether either the male

or female actually desire a short-term, as opposed to long-term,

relationship. As G&S mention, the research of Buss and Schmitt

(1993) indicates that females may use short-term matings as a way

of attracting long-term mates. Further, short-term matings that

occur in novel environments (e.g., interactions initiated in anony-

mous single bars under the influence of alcohol and involving

birth control) are not necessarily evidence of evolved short-term

mating tactics in ancestral environments that lacked these fea-

tures.

Answers to survey questions (e.g., Simpson & Gangestad

1991a) are also problematic as measures of sexual desire because

even if the answers are assumed to accurately reflect the subject’s

thoughts and feelings, the reasons for these thoughts and feelings

must still be considered when interpreting the results because

these reasons are likely to vary greatly between males and females.

For example, identical self-reports of the number of sex partners

expected by a male and female may mean very different things be-

cause of the tremendous difference between males and females in

their ability to actually engage in sex with desired partners (see

Symons 1979). Answers concerning attitudes about impersonal

sex are even more problematic as measures of one’s own sexual de-

sires. What is needed to support G&S’s claim that some men lack

a powerful desire for sexual access to a large number of women

but is not provided, is evidence of males who fail to be sexually

aroused by the thought of, or the visual depictions of, short-term

sexual encounters with numerous attractive females.

tion” would seem to be muddied, and we would not expect “men’s

propensity to invest in single, exclusive long-term relationships

[

to] be inversely related to their genetic fitness.”

What’s more, current life history models and data suggest just

the opposite: men’s (and women’s) propensity to invest in single,

exclusive long-term relationships is expected to be directly related

to their genetic fitness – at least to the extent that their genetic fit-

ness contributes to their probability of survival, adaptive growth

and development, and ultimate capacity for leaving descendants.

Research at the intersection of life history theory and attachment

theory suggests that the development of within-sex differences in

both male and female reproductive strategies are contingent on

our evolved (genetic) capacity to be adaptively affected by early

experiences of risk and uncertainty (e.g., Chisholm 1999a; Hill et

al. 1994). Under conditions of low risk and uncertainty, when the

probability of survival, adaptive growth and development, and

leaving descendants is high, the optimal reproductive strategy will

generally be to maximize offspring quality (e.g., by investing in

“single, exclusive long-term relationships”) rather than quantity.

This is because maximizing offspring quality tends to reduce in-

tergenerational variance in reproductive success, which results in

greater long-term fitness than maximizing offspring quantity in

each generation. On the other hand, under conditions of high risk

and uncertainty, when the probability of survival, adaptive growth

and development, and leaving descendants is low, the optimal re-

productive strategy will generally be to maximize offspring quan-

tity (e.g., by engaging in short-term sexual relations with several

partners). This is because maximizing offspring quantity maxi-

mizes the probability of leaving any descendants at all in risky and

uncertain environments. It may be evolutionarily rational to sac-

rifice offspring quality for increased quantity when such a trade-

off reduces the probability of lineage extinction in risky and un-

certain environments (for the full argument see Chisholm 1999b).

The current-future tradeoff, as it is known, may thus account for

within-sex differences in reproductive strategies better than the

tradeoff between “good genes” and “good parenting.

NOTES

1

. G&S credit Thiessen (1994) for this insight but it was originally

Richard Wrangham’s (1980).

2

. G&S credit Alcock (1993) for this concept but it was originally John

Bowlby’s (1969, p. 50).

G&S also fail to provide ethnographic evidence demonstrating

that women anywhere normally tie up multiple male parental in-

“

vestments by confusing the issue of paternity” (Symons 1982, p.

99), or that women regularly lived in environments where male

2

More women (and men) that never evolved

parental investment was ever so unimportant as to be outweighed

by the benefits of short-term matings for good genes, and again no

such evidence exists. They also fail to consider reasons for doubt-

ing that such tactics would have evolved. Although the authors

stress that “one must weigh the benefits in relation to the costs to

appreciate whether and how adaptations evolved during evolu-

tionary history” (sect. 1.3; emphasis in original), they consider only

the possible benefits in suggesting the plausibility of Hrdy’s (1981)

hypothesis that “females may induce paternity uncertainty by hav-

ing multiple mates, possibly leading to more protection or greater

tolerance of offspring by different men” (sect. 1.1). What they fail

to fully consider is that marriage is a cultural universal and “hu-

man sexual impulses were molded in a milieu in which adulterous

wives risked being abandoned, beaten, and even killed (Symons

1982, p. 299). Research among the Ache has supported the view

that although multiple matings by women may lead to greater tol-

erance of offspring “the price to be paid if extramarital affairs are

discovered . . . can be quite high” (Hill & Kaplan 1988, pp. 298–

99). Given such risks incurred by “unrestricted” females and their

offspring, the genetic benefits gained by such tactics would have

a

b

R. Elisabeth Cornwell, Craig T. Palmer,

and Hasker P. Davis

a

Department of Psychology; ^bDepartment of Anthropology, University

of Colorado at Colorado Springs, Colorado Springs, CO 80933.

robincat@msn.com

Abstract: We are not convinced by Gangestad & Simpson that differential

mating strategies within each sex would be greater than such strategies be-

tween sexes. The target article does not provide actual evidence of human

males who do not desire mating with multiple females, or evidence that

the benefits for females of short-term matings with multiple males have

ever outweighed the associated costs.

We are in full agreement with Gangestad & Simpson (G&S) that

recent advances in the identification of “good gene” markers (e.g.,

symmetry) are an important contribution to theories of human

mating. Unfortunately, rather than integrating such information

into the cogent existing theories of the differences between males

and females, the authors appear to attempt to overthrow such the-

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had to have been tremendous to have offset the benefits obtained

effects were generally stronger for males than females, and re-

markably similar to the behaviors associated with testosterone

levels. High testosterone males are more aggressive and have a

higher number of sexual partners (Dabbs & Morris 1990). Testos-

terone tends to produce a rugged, masculine appearance, one

component of male physical attractiveness (Cunningham et al.

1990). In addition, females at midcycle prefer the appearance of

more masculine faces, compared to other times in their cycle

(Penton-Voak et al. 1999).

Could a portion of the relation of FA to behavior be mediated

by testosterone levels? Gangestad et al. (1994) suggested that pos-

sibility by noting that, because high testosterone levels tend to

suppress immune functioning and increase the risk of disease, and

low FA individuals may have robust immune systems, they may be

more capable than others of sustaining a high testosterone level.

A relation between FA and testosterone would be congruent with

the relation between low FA and both physicality (muscularity, ro-

bustness, and vigor) and social dominance.

via long term mating strategies, including male parental invest-

ment and male kinship ties. G&S fail to provide any evidence of

genetic benefits that would sufficiently justify such a trade-off.

In conclusion, new knowledge about the markers of genetic

quality is important because genetic quality almost certainly influ-

ences mating opportunities. Some females obviously engaged in

short-term sex with males during our evolutionary history, and

they may have been more likely to do so with males showing mark-

ers of genetic quality. Males also probably vary to some degree in

their desires for multiple partners, and a male’s genetic quality

may certainly influence his actual numbers of partners. However,

none of these observations are particularly new, and none of them

are incompatible with conventional evolutionary models of human

sexuality (Buss 1994b; Trivers 1972) or the claim that “with respect

to sexuality, there is a female human nature and a male human na-

ture, and these natures are extraordinarily different” (Symons

1

979, p. v).

The inverse relation between male FA and body mass (Manning

995) also might follow from a testosterone (or growth hormone)

1

interpretation, but raises a measurement question about the rela-

tion between FA and size. FA is typically calculated as the differ-

ence between right and left side features, divided by the average

of the left and right measurements to standardize relative to total

characteristic size. This is an appropriate calibration, but it also

means that asymmetries of the same absolute magnitude at birth

may produce lower FA scores for larger than for smaller people in

adulthood, depending on the growth process.

Low FA indicates the accurate translation of genotype into

phenotype. Relations with other forms of fitness, such as size and

muscularity, require further analyses. Females are known to pre-

fer males who exemplify sexual dimorphism, who are tall, large-

chested and mesomorphic (Beck et al. 1976; Graziano et al. 1978;

Shepard & Strathman 1989). The effect of height was partialled

out in some of the cited studies, while body mass and mesomorphy

were addressed less frequently (Gangestad & Thornhill 1997a). A

simple way to consider this question is: Would women prefer a

man who is short and thin, with a receding chin, but who has sym-

metrical body features (low FA), over a tall, mesomorphic man,

with a square chin, who has asymmetrical features (high FA)? In

evaluating that issue, it would be interesting to know if the effect

of asymmetry is linear across all FA scores, or if there is a thresh-

old effect, with little impact across lower FA scores, but marked

impact as FA becomes extreme.

As a third focus, G&S suggest that pathogen prevalence inclines

women toward a “good gene” mate selection strategy, whereas the

need for paternal investment inclines women toward a “good

provider” mate selection strategy. That is a provocative extrapola-

tion from the animal literature. But conceptualizing long-term re-

lationships primarily in terms of material benefits to the offspring

or mate may obscure some of the species-typical mate dynamics

of homo sapiens.

To sustain a long life-span, allowing individuals to provide con-

tinuing care and encouragement to children, grandchildren, and

other kin, it is valuable to have an emotionally supportive mate

(Cunningham & Barbee, in press). Our research indicated that

both males and females seek partners who exchange high levels of

emotional support and communication, and that is rated as more

desirable in a long-term mate than either good genes or good

provider qualities (Cunningham et al. 1999).

Adaptive flexibility, testosterone, and mating

fitness: Are low FA individuals the pinnacle

of evolution?

Michael R. Cunningham

Department of Psychological and Brain Sciences, University of Louisville,

Louisville, KY 40292. michael.cunningham@louisville.edu

www.louisville.edu/~mrcunn01

Abstract: The expansion of human evolutionary theory into the domain

of personal and environmental determinants of mating strategies is ap-

plauded. Questions are raised about the relation between fluctuating

asymmetry (FA), testosterone, and body size and their effects on male be-

havior and outcomes. Low FA males’ short-term mating pattern is consid-

ered in the context of an evolved tendency for closer and longer human

relationships.

The Gangestad & Simpson (G&S) team have contributed some of

the most creative and intriguing work in evolutionary social psy-

chology, and the current article continues that tradition.

First, the target article extends the analysis of how male and fe-

male mating strategies involve flexible trade-offs due to various

contingencies. Others suggested that individuals engage in trade-

offs of desirable mate qualities in a potential partner, such as

youthfulness versus maturity (Cunningham et al. 1997) and agree-

ableness versus dominance (Jensen-Campbell et al. 1995). G&S

went beyond individual decision-making to explore how ecologi-

cal variables, such as parasite prevalence and resources, influence

the importance placed on various mate selection qualities. The ca-

pacity of both genders to employ various mate selection strategies

adaptively is a useful correction to a literature that tends to

overemphasize male interest in physical appearance and female

interest in wealth.

Second, G&S suggested that one of the most important vari-

ables affecting individual mating strategies is the individual’s at-

tractiveness to the opposite sex, which is linked to fluctuating

asymmetry (FA). The impact of mutations and disease on FA,

and the effect of FA on mating success, is clear in the animal lit-

erature. The human parallels are fascinating: males with low FA

appear to have a higher number of lifetime sexual partners, in-

cluding extra-pair partners; they more reliably stimulate female

orgasms; smell more attractive to females who are in the fertile

phase of their menstrual cycle; and boast about themselves while

belittling their competitors to obtain a date.

If low FA males are the most physically fit and desirable, then

they could be said to be the pinnacle of human evolution. Is there

any way to reconcile our belief that humans have generally been

evolving toward closer, longer relationships, with the reported

tendency of the highly fit, low FA males to pursue a short-term

mating strategy and sexually unrestricted life style? Do only those

males who are less fit exemplify loyalty and supportiveness (cf.

Simpson et al. 1999)?

Most human variation in FA is difficult to see, raising the ques-

tion of the mediators of the relation between FA, behavior, and

mating outcomes. Although FA is correlated with facial physical

attractiveness and intelligence, the correlations seemed too small

to carry all of the effects (Shackleford & Larsen 1997). Behavioral

Perhaps some of the observed differences between low and

high FA people were owing to a minority of high testosterone,

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Commentary/Gangestad & Simpson: Evolution and human mating

highly unrestricted males. Perhaps most low FA individuals are

relatively agreeable, empathic, and disinclined to cheat on their

partners. That might be determined by examining outcomes

based on modal responses rather than group means (cf. Miller &

Fishkin 1997). Another possibility is that low FA males employ a

mixed strategy, pursuing short-term mating at one point in their

lives, and a more committed long-term strategy with greater ma-

turity. Or, on a more misandronistic note, perhaps low FA males

act the way all males would if they were unconstrained: seeking

closeness, support, and loyalty from their partner, but retaining

the possibility of pursuing an unrestricted lifestyle if they meet a

desirable new mate.

of quality differences in negotiations over parental effort (McNa-

mara et al. 1999b). Our point is that no simple prediction can be

made about the optimal allocation of parental resources to mating

and parental effort, as a function of self and partner quality, when

quality is based on variables such as parenting ability, heritable dis-

ease resistance, and current energetic reserves.

A simple example may make this clear. In section 1.1, G&S

mention the idea that by having many mates a female may reduce

the probability that a given male is the father and that as a result

males may be more tolerant or protective towards offspring (Hrdy

1981). But under some circumstances, reduced probability of pa-

ternity may reduce paternal care (e.g., Houston 1995; Westneat &

Sherman 1993). Even in the absence of quality differences, the re-

lationship between paternity and the total help that the female re-

ceives may depend on details of the fitness functions (Houston et

al. 1997). The effects of paternity, parental ability, and energy re-

serves on evolutionarily stable levels of care have not been ex-

plored.

Regardless of those concerns, G&S have provided insightful il-

lumination of the complex terrain of environmental challenges

and sexual opportunities, while making an engaging case that the

fittest individuals have the most choices in that domain.

Although G&S paint a convincing picture that fluctuating asym-

metry (FA) serves as an all-embracing measure of individual qual-

ity, there are problems. First, there are serious doubts that it does;

second, even if it does, this may not be particularly useful to stu-

dents of sexual selection. Meta-analyses of the literature on sym-

metry have been vigorously criticised (Houle 1997; Palmer 1999).

There have been over 100 studies of the relationship between

symmetry and attractiveness, but only a handful are experimental

manipulations which rule out confounding variables, and even

these give equivocal results (Swaddle 2000, pp. 339–59). The best

that can be said of FA and relationship to either attractiveness or

viability in non-human animals is “not proven,” and recent re-

search on human facial attractiveness would actually suggest that

symmetry is not the primary determinant (Scheib et al. 1999).

However, even if there proves to be a consistent relationship be-

tween symmetry and fitness, the very sensitivity of FA to so many

factors affecting development may make it unsuitable for the re-

search programme G&S’s article suggests. If asymmetry is a gen-

eral indicator of fitness, it may have limited usefulness as an indi-

cator of specific qualities. The possibility that males and females

chose mates for specific qualities (good parent, heritable disease

resistance), dependent upon their own phenotypes and geno-

types, is perhaps the most exciting line of future research sug-

gested by Gangestad & Simpson’s target article; but this will

require more sensitive markers of the many facets of quality

than FA.

Mating systems and fluctuating asymmetry:

Firm foundations?

Innes C. Cuthill and Alasdair I. Houston

Centre for Behavioural Biology, School of Biological Sciences, University of

Bristol, Bristol BS8 1UG, United Kingdom; i.cuthill@bristol.ac.uk

a.i.houston@bristol.ac.uk

www.bio.bris.ac.uk/research/behavior/behavior.htm

Abstract: Gangestad & Simpson review sexual selection theory and dis-

cuss their work on fluctuating asymmetry and mate preference in humans.

We question some aspects of their account and mention problems with the

data. We also suggest that more theoretical work on complex but realistic

mating systems is required.

We are glad that Gangestad & Simpson (G&S) go beyond the

naive view that all humans of a given sex should behave in one way.

They have made a serious attempt to relate human sexual behav-

iour to evolutionary models of nonhuman behaviour, an approach

with which we are sympathetic. However, we do not feel that the

base from which they extrapolate to humans is as well founded as

they imply, either in terms of the theoretical predictions, or the

empirical patterns observed in nonhuman studies. Many of the

ideas in their target article lead to important research questions

that have not been tackled adequately in theory or experiment

with nonhuman animals, far less our own species, and thus result

in a challenging research programme for sociobiology as a whole.

In the first part of the target article, G&S outline sexual selec-

tion theory, but their account is selective. There are two notewor-

thy omissions from the list of possible models of preference. One

is Fisher’s runaway process. This is perhaps not surprising – in-

terest in this process seems to have waned. What is surprising is

that there is also nothing on sensory biases. This is the idea that

male attractiveness may depend on properties of the sensory sys-

tem of females that are adaptive in other contexts or are not adap-

tive at all (Ryan 1990; 1997). Preference for symmetry in the con-

text of mate choice may be the result of a sensory bias in favour of

symmetrical forms (Ryan 1997; Swaddle & Cuthill 1994). G&S

emphasise good genes as a basis for extrapair matings, but Enquist

et al. (1998) have argued that such matings can be maintained

without the need to invoke good genes.

A few tips on hypothesis testing

Jennifer Nerissa Davis

Innovationskolleg Theoretische Biologie, Humboldt University, 10115 Berlin,

Germany davis@itb.biologie.hu-berlin.de

itb.biologie.hu-berlin.de/

Abstract: Gangestad & Simpson’s account of the role of good-gene sexual

selection in conditional human mating strategies is reasonably convincing,

but could be more so with a little more attention to (1), dropping unnec-

essary sub hypotheses and especially (2) the inclusion of alternative evo-

lutionary explanations.

Gangestad & Simpson (G&S) have provided us with a carefully

constructed account of human mating strategies. They have built

a monument to the validity of using good-gene sexual selection

theory to explain conditional human mating strategies. They pro-

vide us with a profusion of data consistent with their conclusions.

All of this makes for a lengthy, detailed, and consistent story.

Although they have already done so much, there are at least two

more things they need to do if they want to insure that their con-

clusions are built upon a solid foundation. Both concern their

treatment of hypotheses.

A complete account of mating preferences and patterns of care

involves several levels of interaction. For example, an animal’s de-

cision about whether to divorce its partner depends on the qual-

ity of available mates, which in turn depends on divorce decisions

(

McNamara et al. 1999a). Although G&S are not very explicit

about these interdependencies, they do touch on them in their

discussion of the interaction between male and female patterns of

choice (e.g., sect. 5.5). Situations as complex as those considered

by G&S are relatively unexplored from a theoretical perspective.

Theory has only recently been developed to investigate the effect

Take the hypothesis in section 5.7.1 about the relationship be-

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Commentary/Gangestad & Simpson: Evolution and human mating

tween women’s mating tactics and the need for biparental care to

In their theory of human mating, Gangestad & Simpson (G&S) at-

tempt to account for a wider variety of phenomena than have

other evolutionary psychologists. Nonetheless, because their the-

ory neglects important determinants of mating that are not a prod-

uct of genetically based programs, they go beyond existing evi-

dence in arguing for trade-offs between mates’ genetic fitness and

their proclivity to become family men who are securely attached

to their wives and children.

Because humans’ environment of evolutionary adaptedness

(EEA) encompassed highly variable conditions that impinged in

differing ways on hominids’ reproductive behavior (e.g., Irons

1998), humans manifest a wide range of different solutions to the

problems of reproduction and survival. Humans’ reproductive

behavior is marked by behavioral flexibility, and many aspects of

mating and parenting are free to vary in response to social learn-

ing and multiple aspects of the contemporaneous environment.

Nonetheless, some decision rules for mate choice would have

been sufficiently general-purpose that they may well have become

encoded genetically. In agreement with G&S, these inherited pro-

grams may include a tendency to seek strong and healthy mates

and avoid weak and diseased mates.

A reinterpretation of the evidence that G&S offer follows from

minimalist assumptions that humans are genetically endowed with

a general motive to mate, which operates in conjunction with the

tendency to seek strong and healthy mates and avoid weak and un-

healthy mates. From this perspective, women’s tendency to en-

gage in short-term mating with men marked by low fluctuating

asymmetry (FA) does not require the assumption of trade-offs be-

tween child-rearing and mating or of an inherited contingent de-

cision rule. Instead, a plausible alternative theory follows from

first assuming that women find men high in FA relatively unap-

pealing, because women follow the rule about avoiding mates who

are weak and potentially diseased. To the extent that high FA men

manifest abnormalities and weaknesses, women generally avoid

them for both short-term and long-term mating.

The second assumption required for this alternative theory is

that, with respect to sexual behavior, there are two types of men

who are low in FA; these types reflect, not differences in genetic

quality, but different conditions of rearing in their families of ori-

gin. Consistent with evidence provided by Draper and Harpend-

ing (1988) and Miller and Fishkin (1997), men’s sexual behavior

echoes the security of their bonding with caretakers in their fam-

ilies of origin. Men who were insecurely attached to their own par-

ents have difficulty forming enduring relationships with women

and instead are vulnerable to becoming promiscuous, philander-

ing men who invest minimally in their partners and offspring. Men

who experienced more favorable parenting are more likely to form

stable, monogamous marriages and to invest in their children.

For short-term mating, women seeking sexy, healthy, attractive

partners would have little option but to pair with promiscuous,

philandering men, because such men are readily available for sex-

ual encounters, whereas securely attached men are typically un-

available. Therefore, the reason that FA is correlated with indica-

tors of mating success is, in part, that high FA men have difficulty

attracting women under any arrangements. The promiscuous sub-

type of low FA men also help produce the negative association be-

tween FA and mating success, because these men have multiple

relationships. In contrast, the securely attached subtype of low FA

men dampen this association somewhat, because they have rela-

tively few partners, although probably more than the high FA

men, who are unappealing to women for short-term and long-

term mating. The rather weak correlations that G&S cite between

FA and variables such as number of sexual partners and invest-

ment in relationships are fully consistent with this reasoning.

Other types of empirical evidence would be required to distin-

guish between G&S’s theory and the alternative that I propose.

According to this alternative theory, promiscuous men do not

offer better genes than men who are securely bonded to their

mates. Also, the aggregate reproductive success of men in the two

groups may be comparable because promiscuous men’s casual

raise children. Ask yourself the following question: If the hypoth-

esis that women raised in single parent households adopt short-

term mating strategies because they have been provided with cues

that long-term stable pair-bonds are unnecessary was proved false,

where would that leave the validity of good gene sexual selection

(

GGSS)? For that matter, where would it leave the more local pre-

diction about the relation between women’s childhood experi-

ences and adult mating tactics? If your answer is: in the same place

they would be if it were true, then you’ve gotten my first point.

Whether the adoption of short-term mating tactics by women in

this situation is owing to them thinking they do not need paternal

care, or thinking they are in an environment where long-term sta-

ble pair-bonds are rare is certainly an interesting question, but it

is irrelevant to the point G&S need to make, which is simply that

women’s mating tactics do vary, and vary along dimensions con-

sistent with GGSS.

On the other hand, if this behavior turns out to be the nonadap-

tive outcome of a usually adaptive developmental mechanism, it is

time to worry. This brings me to my second point, which concerns

the explication of alternative hypotheses. G&S’s conclusions would

be much tighter if they spent more time, or even any time, trying

to generate and test their theory against alternative evolutionary

hypotheses. For example, they mention the relationship between

men’s physicality and fluctuating asymmetry (sects. 4.4 and 5.2)

two factors which they claim are highly correlated. They also cite

several authors (Hrdy 1981; Mesnick 1997; Smuts 1985; Wilson &

Mesnick 1997) for the idea that women may have evolved to pre-

fer men who could provide them with protection from other, ag-

gressive men, but they take this argument no farther. Wouldn’t the

argument that women’s short and long term mate preferences have

evolved as a means of minimizing physical danger to themselves

and their children be a reasonable alternative hypothesis to GGSS?

Given the relationship between physicality measures and fluctuat-

ing asymmetry, wouldn’t this alternative hypothesis also be consis-

tent with their data? Perhaps physicality is not simply a mediating

factor of symmetry; perhaps it is the central factor. Until they ad-

dress it, and others like it, directly pitting them against GGSS; it’s

hard to take GGSS as a proven, or even uniquely supported, the-

ory of human mate choice.

Just one more small point, unrelated to the preceding discus-

sion, yet something I cannot let slip by. Most of the evidence they

provide is correlational, and, given their subject matter, providing

anything experimental would certainly be difficult. Although they

do a good job of interpreting their results, a few conflations of cor-

relation with causation do slip through (e.g., their discussion of

extra-pair paternity in birds (sect. 3.3, para. 7).

I would hate this criticism to leave the impression that I believe

G&S’s work to be neither valuable nor important. Mate choice is

one of the best studied topics in evolutionary psychology, and their

treatment of it in this paper, and especially their focus on condi-

tional mating strategies, is a major contribution to it. It is, in fact,

precisely for this reason that I feel the need to urge them to take

what is already very good and make it even better.

Do Don Juans have better genes

than family men?

Alice H. Eagly

Department of Psychology, Northwestern University, 2029 Sheridan Road,

Evanston IL 60208-2710 eagly@nwu.edu

www.psych.nwu.edu/psych/people/faculty/eagly/

Abstract: An alternative interpretation of Gangestad & Simpson’s findings

features the assumption that only a subgroup of those men who are low in

fluctuating asymmetry are typically available for short-term mating. In

general, these philandering men do not offer higher genetic quality than

men who are securely attached to long-term mates.

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Commentary/Gangestad & Simpson: Evolution and human mating

matings with many women are balanced by bonded men’s en-

hancement of the health and welfare of a single mate and her off-

spring, who are then more likely to survive. Moreover, a contin-

gent genetic program driven by good genes selection does not

underlie women’s tendency to form short-term relationships with

promiscuous men. Rather, women are interested in sexual affairs

when their primary mateship is damaged, ordinarily because it is

sexually or emotionally unsatisfying. Sometimes this damage

follows from a woman’s bad luck in attempting her primary rela-

tionship with a low FA man who has difficulty with long-term at-

tachments. The cost-benefit analysis that then guides the sexual

decision-making of women with damaged mateships would incor-

porate various considerations, including sexual desirability (low

FA men tend to be sexually appealing) and ease of establishing

short-term relationships (men from the promiscuous subgroup of

low FA men tend to be available).

Other utilities guiding women’s sexual decision-making would

take into account the likely consequences of a sexual affair. These

consequences may include being stigmatized in their community

and alienating a long-term mate who contributes fathering and

other valued resources to the family. These perceived utilities are

constrained by social norms that govern family life and sexuality,

which may differ for women and men. As Eagly and Wood (1999)

argued, in societies in which men and women occupy distinctively

different social roles, the sexes perceive different utilities and have

somewhat different mating preferences. The mating preferences

and behaviors of women and men are more similar when they oc-

cupy more similar positions in the social structure. More gener-

ally, the context for human sexuality is a community that estab-

lishes family roles, defines allowable sexual behavior, and specifies

appropriate mate choices.

evolutionary models. If we are to “understand the psychological

architecture that guides social interactions” (Introduction) it is

critical that the investigation include the available data from those

organisms which are phylogenetically, physiologically, and behav-

iorally closest to our species.

In the target article, G&S suggest that good genes sexual selec-

tion (GGSS) and good parenting sexual selection are the main fac-

tors in the evolution of variation in human mating patterns. They

rely heavily on basic behavioral ecological concepts of male and

female sexual strategies (Buss & Schmitt 1993; Trivers 1972) and

studies of fluctuating asymmetry (FA) in humans and birds to con-

vey their hypotheses.

Data from recent primatological studies suggest that the tradi-

tional examination of male mating and parental investment has

overlooked the wide and costly array of physiological and social

mechanisms. Physiological studies on a wide range of primate

species (see Berkovitch 1991; 1999, for a review) have demon-

strated greater pre-mating investment on the part of males than

previously considered (i.e., based on Trivers 1972). An examina-

tion of the physiological and social pre-mating investment mech-

anisms in primate males (including humans) would add to, and

broaden G&S’s model and could affect their assessments of male

and female choice as it relates to parental investment (a major

component of their conclusions).

Relying on fluctuating asymmetry as “the best available mea-

sure” (sect. 3.3) to test the Good Genes Sexual Selection model is

overlooking data from primate studies. For example, Fox et al.

(1999) reported lack of support for “good genes” hypothesis in

mating patterns in a long-term study of orangutans in Sumatra.

Extra-pair copulations (epc) in pair-bonded species are frequently

examined in discussions of “good genes” models, yet G&S do not

refer to the wide range of recent work on epc’s in pair-bonded pri-

mates (Brockleman et al. 1998; Palombit 1996, 1999; Reichard &

Sommer 1997). Interesting to note, the correlation between men’s

FA and extra-pair sex partners reported by G&S (r ϭ Ϫ.17, sect.

Human mating models can benefit

from comparative primatology

and careful methodology

4

.2) is rather low.

G&S utilize examples from studies on Zebra Finches and Barn

Swallows to support their discussion of FA in humans. The meta-

analysis (Moller & Thornhill 1998a) of FA on which G&S rely for

their support of GGSS is heavily biased by avian and insect stud-

ies with only five mammalian species, and no primates aside from

humans, represented in the data set. Given the wide differences

in morphological adaptation across taxonomic classes, the useful-

ness of this comparative tool is debatable without the inclusion of

additional mammalian studies.

A brief review of the primatological literature is of particular

relevance to section 4.5 (Evidence for women preferring sym-

metrical men for their gametes). For example, the target article

cites one study in which female macaques orgasm more frequently

with dominant males (Troisi & Carosi 1998) for primatological ev-

idence in support of the assertion that female orgasm favors more

symmetrical males in humans. However, van Noordwijk (1985)

demonstrated there was no consistent relationship between fe-

male orgasm and macaque male dominance, and recent work by

G. Goldstein and myself also reveals a lack of correlation between

female orgasm and male rank in macaques (unpublished data).

Additionally, G&S rely on Bellis and Baker’s (1990) reports of hu-

man epc’s during peak fertility (based on interviews and ques-

tionnaires), but do not include data from field observations of

other primates’ epc patterns (i.e., Brockleman et al. 1998; Palom-

bit 1996; 1999; Reichard & Sommer 1997).

Agustin Fuentes

Primate Behavior and Ecology Program, Department of Anthropology,

Central Washington University, Ellensburg, WA 98926-7544.

afuentes@cwu.edu

www.cwu.edu/~primate

Abstract: Conditional mating strategies and within-sex variation in mat-

ing patterns occur across a wide range of primate taxa. Attempts to model

the evolution of human mating strategies should incorporate current pri-

matological data sets and phylogenetic perspectives. However, compar-

isons between interview and questionnaire-based human behavioral data

and observationally and experimental generated nonhuman behavioral

data should be conducted with prudence.

Conditional mating strategies and within-sex variation in mating

patterns are not unique to humans but are prevalent across a

broad range of primate taxa, and the examination of these patterns

is critical to modeling of the evolution of social organization.

When searching for the set of behaviors apparent in any period of

human evolution (such as the Environment of Evolutionary Adap-

tiveness, EEA, for example) a phylogenetic perspective across

primate taxa will facilitate a robust set of hypotheses regarding the

evolutionary sequences of current behavior (Rendall & DiFiore

1

995). I applaud Gangestad & Simpson’s (G&S’s) attempt to

model the variation and trade-offs that have molded human mat-

ing strategies over the course of our evolutionary history and to

posit actual mechanisms for these strategies. This interest in vari-

ation in mating patterns and strategies is well in line with current

reanalyses of mating systems across a number of taxa (Black 1996;

Fuentes 1999b; Henson & Warner 1997). However, their primary

reliance on human interview data and extrapolations from the

avian literature ignores the diversity of primatological data rela-

tive to their inquiry and weakens their ability to effectively design

There is a diverse and growing body of literature specifically re-

garding pair bonds, monogamy, and mating patterns in primates

(see Fuentes 1999a; 1999b for reviews). There has also been a di-

versification in the literature concerning the evolution of human

social organization, especially in regard to child rearing invest-

ment by nonparents and other aspects of social organization (see

Bird 1999; O’Connell et al. 1999). The inclusion of primatological

and human evolutionary literature would enhance G&S’s attempts

to model the causal factors behind human mating patterns and po-

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