Review Article
Beauty and the beast: mechanisms of sexual selection in humans

https://doi.org/10.1016/j.evolhumbehav.2010.02.005Get rights and content

Abstract

Literature in evolutionary psychology suggests that mate choice has been the primary mechanism of sexual selection in humans, but this conclusion conforms neither to theoretical predictions nor available evidence. Contests override other mechanisms of sexual selection; that is, when individuals can exclude their competitors by force or threat of force, mate choice, sperm competition, and other mechanisms are impossible. Mates are easier to monopolize in two dimensional mating environments, such as land, than in three-dimensional environments, such as air, water, and trees. Thus, two-dimensional mating environments may tend to favor the evolution of contests. The two-dimensionality of the human mating environment, along with phylogeny, the spatial and temporal clustering of mates and competitors, and anatomical considerations, predict that contest competition should have been the primary mechanism of sexual selection in men. A functional analysis supports this prediction. Men's traits are better designed for contest competition than for other sexual selection mechanisms; size, muscularity, strength, aggression, and the manufacture and use of weapons probably helped ancestral males win contests directly, and deep voices and facial hair signal dominance more effectively than they increase attractiveness. However, male monopolization of females was imperfect, and female mate choice, sperm competition, and sexual coercion also likely shaped men's traits. In contrast, male mate choice was probably central in women's mating competition because ancestral females could not constrain the choices of larger and more aggressive males through force, and attractive women could obtain greater male investment. Neotenous female features and body fat deposition on the breasts and hips appear to have been shaped by male mate choice.

Introduction

Viewing human mating in a developed nation, one surmises that success in heterosexual competition for mates entails attracting members of the opposite sex. Beauty, fashion, and physical fitness are so important in places like the United States that they have become multi-billion dollar industries. Men and women have virtual autonomy to choose their mates. These conditions are so pervasive that it is tempting to think that they have characterized our evolution—that humans evolved in a context where, in the mating arena, the preferences of the opposite sex were the primary forces shaping our phenotypes.

With notable exceptions (e.g., Apostolou, 2007, Archer, 2009, Buss and Dedden, 1990, Buss and Duntley, 2006, Buss and Shackelford, 1997, Daly and Wilson, 1988, Lassek and Gaulin, 2009, Sell et al., 2009), the recent literature in evolutionary psychology reinforces this impression. The vast majority of research on sexual selection in Homo sapiens focuses on mate choice. Of papers on human sexual selection, more than 75% (55 of 73) published from 1997 to 2007 in the journals Evolution and Human Behavior and Human Nature mainly concern mate choice (categorized by the present author and a trained research assistant into “mate choice,” “dominance and status competition,” and “other,” according to the hypotheses tested in the paper). According to an influential researcher, in sexual species, “all genes must propagate through the gateway of sex, and mate choice is the guardian of that gateway. For this reason, sexual courtship was probably central in human evolution and remains central in modern human life” (Miller, 1998, p. 119). According to another leading researcher, “the desires of one sex establish the critical dimensions along which members of the opposite sex compete” (Buss, 1996, p. 307). The extensive evidence leaves little doubt that the preferences of each sex have been important selection pressures on the other.

But has mate choice been the primary mechanism of human sexual selection, as the literature might suggest? I argue here that it has not. Rather, contest competition—in which force or threats of force are used to exclude same-sex rivals from mating opportunities—has been the main form of mating competition in men, whereas male mate choice has predominated as a mechanism of sexual selection operating on women. This argument will be built on theory developed from cross-species comparison and subsequently tested by examining evidence of apparent design in humans.

Section snippets

Sexual selection

Darwin, 1859, Darwin, 1871) proposed sexual selection to explain traits that seemed harmful to survival—the hooked jaw of the male salmon, the stag's antlers, the cock's spurs, and the “gorgeous plumage” and “strange antics” (1859, p. 137) of the male rock-thrush and bird of paradise, for example. Although these traits might impair survival, Darwin postulated that they could nevertheless promote their own passage into the next generation by helping their bearers win mating opportunities: They

Sexual selection in humans

Women invest more in offspring than men do through gestation and nursing for up to several years in foraging societies (Eibl-Eibesfeldt, 1989) and through providing more parental care on average in all known societies (Hewlett, 1992). Greater investment slows women's reproductive rates, skewing the operational sex ratio so that there are more males than females available for mating. Across species, these conditions foster mating competition in the more rapidly-reproducing sex. Evidence suggests

Summary

The ancestral human mating system may have comprised groups of (often related) males cooperating in female defense. Between-group aggression, female cooperation, and the ability to inflict lethal injuries with weapons likely enabled some males to monopolize multiple females. At the same time, female defense was imperfect, promoting moderate sperm competition and female choice of both long-term mates and extra-pair sex partners. Monopolization of females was probably related to social skills and

Conclusions

Human mating is complicated. It is the stuff of operas and soap operas, full of manipulation and deception, aggression and solicitude, cooperation and selfishness. It is the culmination of multiple individual interests, sometimes overlapping, often opposing. Human mating is perhaps even more complicated than it appears in contemporary industrial societies, where men and women choose their mates largely beyond the authority of kin, women do not rely economically on men, and men are prohibited by

Acknowledgments

I thank Drew Bailey, Mike Bailey, David Buss, Khytam Dawood, Steve Gaulin, Martie Haselton, Jeffrey Kurland, and an anonymous reviewer for their helpful comments on previous drafts; and Eric Seemiller and Lauren Catalano for their assistance with literature review.

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