Contemporary mate preferences can provide important clues to human reproductive history. Little is known about which characteristics people value in potential mates. Five predictions were made about sex differences in human mate preferences based on evolutionary conceptions of parental investment, sexual selection, human reproductive capacity, and sexual asymmetries regarding certainty of paternity versus maternity. The predictions centered on how each sex valued earning capacity, ambition— industriousness, youth, physical attractiveness, and chastity. Predictions were tested in data from 37 samples drawn from 33 countries located on six continents and five islands (total N = 10,047). For 27 countries, demographic data on actual age at marriage provided a validity check on questionnaire data. Females were found to value cues to resource acquisition in potential mates more highly than males. Characteristics signaling reproductive capacity were valued more by males than by females. These sex differences may reflect different evolutionary selection pressures on human males and females; they provide powerful cross-cultural evidence of current sex differences in reproductive strategies. Discussion focuses on proximate mechanisms underlying mate preferences, consequences for human intrasexual competition, and the limitations of this study.

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Sex differences in human mate preferences: Evolutionary hypotheses tested in 37 cultures

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.

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The evolution of human mating: Trade-offs and strategic pluralism

The study of human sexuality from the darwinian perspective is in an explosive phase. Recent research is diverse; for instance, the dynamics of heterosexual relationships, the role of honest advertisement in attractiveness, the role of fluctuating asymmetry in sexual competition, and sexual conflict over fertilization, seen in sperm competition adaptations of men and possible cryptic sire-choice adaptation of women. Also, recent research reveals that the sexual selection that designed human secondary sexual traits was functional rather than strictly fisherian.

The evolution of human sexuality.

The Sociosexual Orientation Inventory (SOI; Simpson & Gangestad 1991) is a self-report measure of individual differences in human mating strategies. Low SOI scores signify that a person is sociosexually restricted, or follows a more monogamous mating strat- egy. High SOI scores indicate that an individual is unrestricted, or has a more promiscuous mating strategy. As part of the International Sexuality Description Project (ISDP), the SOI was translated from English into 25 additional languages and administered to a total sam- ple of 14,059 people across 48 nations. Responses to the SOI were used to address four main issues. First, the psychometric properties of the SOI were examined in cross-cultural perspective. The SOI possessed adequate reliability and validity both within and across a di- verse range of modern cultures. Second, theories concerning the systematic distribution of sociosexuality across cultures were evaluated. Both operational sex ratios and reproductively demanding environments related in evolutionary-predicted ways to national levels of so- ciosexuality. Third, sex differences in sociosexuality were generally large and demonstrated cross-cultural universality across the 48 na- tions of the ISDP, confirming several evolutionary theories of human mating. Fourth, sex differences in sociosexuality were significantly larger when reproductive environments were demanding but were reduced to more moderate levels in cultures with more political and economic gender equality. Implications for evolutionary and social role theories of human sexuality are discussed.

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Sociosexuality from Argentina to Zimbabwe: a 48-nation study of sex, culture, and strategies of human mating.

Historically, the reasons people have sex have been assumed to be few in number and simple in nature-to reproduce, to experience pleasure, or to relieve sexual tension Several theoretical perspectives suggest that mo- tives for engaging in sexual intercourse may be larger in number and psychologically complex in nature Study 1 used a nomination procedure that identified 237 expressed reasons for having sex, ranging from the mundane (eg, ''I wanted to experience physical pleasure'') to the spiritual (eg, ''I wanted to get closer to God''), from altruistic (eg, ''I wanted the person to feel good about himself/herself'') to vengeful (eg, ''I wanted to get back at my partner for having cheated on me'') Study 2 asked participants (N = 1,549) to evaluate the degree to which each of the 237 reasons had led them to have sexual intercourse Factor analyses yielded four large factors and 13 subfactors, producing a hierarchical taxonomy The Physical reasons subfactors included Stress Reduction, Pleasure, Physical Desirability, and Experience Seeking The Goal Attainment subfactors included Resources, Social Status, Revenge, and Utilitarian The Emotional subfactors included Love and Commitment and Expression The three Insecurity subfac- tors included Self-Esteem Boost, Duty/Pressure, and Mate Guarding Significant gender differences supported several previously advanced theories Individual differences in expressed reasons for having sex were coherently linked with personality traits and with individual differences in sexual strategies Discussion focused on the complexity of sexual motivation and directions for future research

Why Humans Have Sex

Alexander (1979) has invited “. . . biologists to contribute to the analysis of human behavior on all legitimate fronts. . .” He considered it “. . . especially relevant that [they] take up the problem of relating human attributes to evolutionary history.” The analysis of human sexual behavior surely qualifies as a legitimate topic in evolutionary biology. This chapter represents a contribution to the argument that sperm competition does occur in humans and has been a selective force in the evolution of certain human characteristics. There has been considerable controversy over what may be the “natural” sexual inclinations (promiscuous, polygynous, serially polygynous, monogamous, or some mixture of these) of human males (e.g., Trivers 1972; Wilson 1975; Alexander 1977; Short 1977, 1979, 1981; Daly and Wilson 1978; Symons 1979; Lovejoy 1981; Barash 1982; Harvey and Harcourt, this volume), but relatively much less debate over the sexual predilections of human females (Hrdy 1981). Females are widely assumed to be monogamous, with little formal recognition of alternative female strategies (but see Hrdy 1981, and Knowlton and Greenwell, this volume). The compromise view of human male mating strategy proposes mixed tactics (Trivers 1972) where males attempt to pair-bond with one or more females by high investment, and opportunistically (more or less promiscuously) mate with other females. All combinations of male tactics from rape (Shields and Shields 1983, Thornhill and Thornhill 1983) to high investment (Trivers 1972) and the environmental and social circumstances that occasion their expression have received analysis in the literature. As Hrdy (1981) observed: “The sociobiological literature stresses the travails of males – their quest for different females, the burdens of intra-sexual competition, the entire biological infrastructure for the double standard. No doubt this perspective has led to insights concerning male sexuality. But it has also

Robert L. Smith

Papers

19 – Human Sperm Competition