THE EVOLUTION OF FEMALE SEXUALITY AND MATE SELECTION IN HUMANS M e r e d i t h F. Small Cornell University

U n d e r s t a n d i n g female sexuality and mate choice is central to evolutionary scenarios of h u m a n social systems. Studies of female sexuality conducted b y sex researchers in the United States since 1938 indicate that h u m a n females in general are concerned w i t h their sexual w e l l - b e i n g and are capable of sexual response parallel to that of males. Across cultures in general a n d in western societies in particular, females engage in extramarital affairs regularly, regardless of p u n i s h m e n t b y males or social d i s a p p r o v a l . Families are u s u a l l y concerned with marriage a r r a n g e m e n t s only insofar as those arrangements are economically or politically advantageous, b u t females most often have a voice in arranged marriages. Extended families also concentrate on a couple's future r e p r o d u c t i o n rather than on sexual exclusivity. A l t h o u g h marriage for females is often c o m p r o m i s e d b y male or f a m i l y reproductive interests (which m a y not in fact differ from female interests), females a p p e a r to exercise their sexuality with more freedom than has p r e v i o u s l y b e e n suggested. N o t i o n s of h u m a n females as p a w n s in the male reproductive game, or as traders of sex for male services, s h o u l d be d i s p e l l e d . KEY WORDS: Female sexuality; Female choice; H u m a n evolution; Mating strategies

Received June 12, 1991; accepted November 11, 1991. Address all correspondence to Meredith F. Small, Department of Anthropology, Cornell University, Ithaca, NY 14853. Copyright 9 1992 by Walter de Gruyter, Inc. New York Human Nature, Vol. 3, No. 2, pp. 133-156. 133

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"Unlike other animals, humans have brought reproduction into the exchange system, but money, status and ceremonies only serve to deceive humans into thinking that something more lofty, more idealistic, more important than reproduction is involved. They can focus on the ceremonial trappings of wealth and power, they can get distracted by the joy of sex and the ecstasy of orgasm, but it is really reproductive biology that is calling the behavioral shots." (Batten 1991) Mating and reproduction are the keys to understanding individual reproductive success. Although culture has presumably had a major impact on the expression of h u m a n sexuality, it is also reasonable to suggest that h u m a n sexuality and mating have been molded, in some degree, by evolution.Humans do not mate at random, and their choices of mating and marriage patterns do result in differential reproductive success regardless of what culture dictates. If we are to find a biological link to human behavior, it should most easily appear at this basic level, during mating, sexuality, and marriage, where genes are passed on. This paper concentrates on female sexuality and mating behavior. Although mate choices by h u m a n females are influenced by social, economic, and psychological factors, there are also certain universal features of h u m a n female mating that make evolutionary sense given the nature of female sexuality and the common direction of female reproductive interests. This arena--human female sexual behavior and mate choice~is difficult to approach for several reasons. First, we have no behavioral record of the evolution of human sexual behavior, only scenario building. Thus we cannot gain a true picture of the ancestral nature of female sexuality. Second, there is no clear picture of current ideas of female sexual response. Female sexuality is deeply embedded in cultural morality, both ethnohistorically and historically. Most women will not freely discuss their sexual history or their attitudes. Cross-cultural reports of h u m a n female sexual and marital patterns are also suspect because sexuality is sometimes impossible to study by an outsider. And third, what women do and what they say they do are often two different things. Nevertheless, a review of the current information, including crosscultural studies and speculations on the evolution of female sexuality, is important. There is no question that h u m a n female sexuality, marriage, and mating display certain universal patterns. Physically, women display few external signals of ovulation, and they are able to participate in sex during all phases of the cycle. Women also have a predictable pattern of sexual response with orgasm. Emotionally, women in all cultures form bonds with men, marry, and have children. Women's concerns over children and family are not necessarily opposed to social forces determining the rules of family construction. Women participate in their own destiny, even if their participation is simple acquiescence.

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I intend to explore two levels of the nature of h u m a n females---the nature of female sexual response and assertiveness, and evidence of mate choice or participation in decisions about marriage and mating patterns by females in several cultures. Although the evolutionary literature in general (and Darwin in particular) has suggested that h u m a n females, like all female animals, are sexually passive compared to males, recent studies suggest that females are highly sexually motivated. Crosscultural studies of female sexual and mating behavior also reinforce the postulated common human female nature by demonstrating female sexual motivation in different cultures. The purpose of investigating these two levels of research on human sexuality is to explore the possible universal nature of human female sexuality and mate choice regardless of the influences of culture and society. H U M A N FEMALE SEXUAL RESPONSE

Human female cycles are characterized as "menstrual" rather than "estrous," yet there is confusion about the difference between an estrous cycle and a menstrual cycle. Estrous cycles are usually defined by the appearance of specific morphological and behavioral traits that occur only during periods when females are fertile (Short 1984). For example, nonhuman primates have estrous cycles because they usually mate only with males during a restricted period of the year; some display morphological cues, such as sexual swellings of perineal area; and most often there is no visible sign of menstruation (Blaffer Hrdy and Whitten 1986). But confusion arises when females with estrous cycles mate during nonestrous periods (Wolfe 1991). H u m a n females have menstrual cycles rather than estrous cycles. They copulate at all phases of the hormonal cycle, although there is some debate about the intensity, initiation, and interest by h u m a n females relative to cycle phase and during pregnancy (Adams et al. 1978; Gebhard and Johnson 1979; Kenny 1973; Udry et al. 1973). Human females are spontaneous (as opposed to reflexive) ovulators and will ovulate regardless of copulation. There is some evidence, however, that the presence of a male (not copulation per se) increases the incidence of ovulatory cycles in modern w o m e n (Veith et al. 1983), and there is speculation that human females will cycle synchronously w h e n residing in close proximity (Adams et al. 1978; Graham 1991; McClintock 1971; Russell et al. 1980). The clitoris is the main organ of arousal and pleasure for human females (Gebhard and Johnson 1979; Hite 1976; Kinsey et al. 1953; Sherfey 1966). Some feel the clitoris is an atavistic feature of females, a morphological gift resulting from an embryonic connection with the male penis (Symons 1979). Their view is based on the fact that the clitoris is an anatomical homolog to the penis; it is made of the same

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tissue and responds sexually in a similar manner (Masters and Johnson 1965b). They also point out that orgasm, or even sexual pleasure, is not necessary for females to participate in sexual intercourse or to reproduce. In other words, a clitoris that enables sexual arousal and orgasm is not necessary for female reproduction and therefore is not a direct result of selection. The penis (as a sperm transfer organ) and male orgasms (with muscle contractions that dispel sperm) are, they argue, necessary for male reproduction, and thus under strong selective pressure. But the male appendage, not found in all animals (most birds, for example, do not have penises), has presumably been selected because of sperm competition, not because of sexual pleasure or because it is the only way to transfer sperm (Parker 1982, 1984). Thus it is unreasonable to suggest that selection for sexual pleasure first occurred in males and then was passed on to females as common baggage (see also Fedigan 1986). Others suggest that human and nonhuman primate females benefit from orgasmic pleasure during intercourse, and thus selection for the clitoris and female orgasm occurred parallel to, not as a result of, selection for male sexuality (Blaffer Hrdy 1979; Fedigan 1986). Given that the human embryo is a female rather than male blueprint, it might be more accurate to suggest that the penis is a homolog to the clitoris. Anticipated sexual pleasure for both sexes is most likely an initiator (a stimulus of sorts) to begin mating behavior. Hite (1976) has provided a most intriguing hypothesis for the appearance and anatomical position of the human clitoris. She suggests the clitoris is situated on the front of the female body, easily accessible and thus easily stimulated, to enhance female initiation and participation in copulation. Orgasm, under this scheme, is a result of extended physiological stimulation but not necessarily the trait selected per se; sexual arousal, by means of the exposed clitoris, is the important functional trait selected through time. Human females are often considered sexually "continuously receptive" (Lovejoy 1981). Some authors have acknowledged the difference between humans and other primates by regarding human females as experiencing a kind of low-key continuous receptivity (Alexander and Noonan 1979). This label, whether in its original or in a qualified form, has influenced most subsequent scenarios of the evolution of human mating and marriage patterns. The term receptivity has been taken (often out of context) from Beach's (1976) definition of estrus in mammals. Beach's original description includes three stages of female estrus: (a) attractivity, whereby females appear attractive to males; (b) proceptivity, which refers to a female's interest in copulation, including female initiation; and (c) receptivity, which refers to a female's positive reaction to male attention, which will facilitate the act of copulation (see also Wolfe 1991). Calling human females "continuously receptive" is inappropriate for two reasons. First, it may be inaccurate to use a term that is indicative

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of an estrous cycle for an animal (humans) with a menstrual cycle. Second, human females may be continuously attractive (in Beach's sense), but they are certainly not continuously proceptive (initiating) or receptive (facilitating). This point is an important one. H u m a n females have been portrayed alternately as acquiescent sexual beings w h o submit to male attentions or as manipulative sexual partners w h o have gained male care by trading sex for favors (see below). Underlying these scenarios is the suggestion that human females are continuously ready for sex and can use that readiness whenever they please. Although no clear answers to the "true nature" of female sexuality may exist, it is reasonable to suggest that female sexual interest is neither seasonal nor episodic, nor is it continuously intense (Adams et al. 1978; Gebhard and Johnson 1979). The most we can say is that human females probably do not emit special pheromones or visual signals that turn off or on male attention, and thus human females might be continuously attractive to males. At the same time, human females are inconsistently proceptive and receptive. The biological or social determinants of that proceptivity and receptivity have yet to be investigated. Masters and Johnson (1965a, 1965b) have described four arbitrary stages of female sexual response. They use the word "arbitrary" because these stages may actually appear as one phase of a complete orgasmic cycle. The stages are excitement, plateau, orgasm, and resolution. The excitement phase is initiated by a visual, physical, or psychic stimulus. The plateau stage is distinguished by tumescence of the breasts, perineum, and vagina. From this phase, females pass rapidly and "with relative ease" to orgasm (Masters and Johnson 1965a, 1965b), and females may experience multiple orgasms as they fluctuate back and forth between the third and fourth stages. The orgasm is an involuntary contraction of the entire perineal body, the outer one-third of the vagina, the rectum, and the lower abdomen. At the same time, the upper portion of the vagina balloons out and may create a hollow feeling (Hite 1976). The clitoris is the organ of stimulation, but the orgasm is manifest in the vagina and the rest of the pelvic area. Resolution may take some time, since it includes detumescence. Masters and Johnson's work is most notable for their acknowledgment of the variation among women, and through time for any individual woman, in these various phases.

WOMEN'S INTEREST IN SEX

Surprisingly little information exists about how, when, and w h y h u m a n females participate in sexual intercourse. Since human females do not have estrous cycles, it is usually assumed that sexuality in h u m a n

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females is less bound by hormonal changes than it is in other animals (Short 1984). But there also seems to be a prevailing, culturally bound notion in western writing, both popular and scientific, that human females are less interested than males in sex, or sex with different partners (Symons 1979). This idea has been reinforced by evolutionary theory. Beginning with Darwin (1859, 1871), especially in the development of sexual selection theory, females were most often portrayed as "shy" and "passive" sexual creatures (Blaffer H r d y 1981; Small 1989a). Darwin even suggested that the reason females were most likely to be choosy sexual partners was not that females were the limiting reproductive resource, as we now know, but that females were simply not interested in sex and were less passionate than males (Darwin 1871; for an example that reinforces the notion of a genetic lower-than-male sex drive, see Gregor 1985). The current picture of female sexual interest described by Darwinians is contradictory. Symons (1979) has suggested that differences exist in human male and female sexual practices, and that these differences are biologically based. He proposes that a desire for sexual variety is an evolutionarily selected strategy for males, whereas females have been selected to be choosy. He uses literary references and cross-cultural data to support his hypothesis. When a female does avail herself of different partners, Symons feels, she does so to improve her chances of conceiving with a new and better male than her husband. Males, on the other hand, desire variety for variety's sake. Since males have relatively more gametes to dispense, copulations with many females would seem an important reproductive strategy. And since females incur heavy investment with each offspring, it makes sense that a human female would be extremely careful about conception. Symons's view makes initial biological sense. His words are echoed by Daly and Wilson (1978). Although they point out that the nonhuman primate female sex drive during estrus can be as strong as the male sex drive, they reiterate the need for females to be more choosy than males when selecting partners. They refer to expected differences in male and female strategies as "the reluctant female and the ardent male" or "the nurturant female and the prodigal male." There are, however, major flaws in Symons's and Daly and Wilson's application of traditional parental investment theory to the human case. First, humans h a v e evolved toward highly dependent offspring. Males, as well as females, must contribute to offspring survival. Male reproductive success, like female reproductive success, is constrained by the demands of care needed to bring offspring to reproductive age. Although some males might benefit from copulations with many females, most males benefit by contributing to the survival of offspring for

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w h o m they Have confidence of paternity (Frayser 1985). In addition, if a female has a choice in terms of the males with w h o m she might copulate, the same evolutionary framework that suggests females will be choosy suggests that this choosiness will select against males w h o do not demonstrate commitment to offspring. Second, h u m a n males have extremely low sperm counts and slow sperm mobility compared with other primates (Small 1988, 1989b). Thus, the potential for conceiving with many females, who do not show external signs of estrus, is relatively low. Third, Symons's data on polygyny, as Frayser (1985) points out, do not support the notion of a biologically wired urge for sexual variety. Polygyny occurs significantly most often in patrilineal societies in which male alliances are an imperative; males marry a number of females to form alliances with the females' kin. In other words, plural marriages, in which males are still restricted to a few females, are the result of social or cultural factors, not sexual desire (Frayser 1985). The fact remains, however, that polygynous marriages are most often formed with nubile and not sterile women, suggesting that fitness (potential offspring) is not incidental in the choice of bride (Betzig 1986). And fourth, Symons's use of a western model of male freedom and female restriction might make intuitive sense only because it comes from our own culture (Frayser 1985). This does not necessarily make it accurate evolutionary history or fact. The data from more female-oriented Darwinians contradict the notion of females as reluctant, choosy sexual partners and support an idea of human females as naturally sexual creatures restricted by social norms. Blaffer Hrdy (1981) relies on nonhuman primate data to paint a picture of female primates as strategizing individuals with their o w n reproductive interests in mind; they are anything but passive, choosy creatures. In terms of sexual behavior, nonhuman primate females are sexually active, are most often interested in a variety of males w h e n their behavior is not restricted by males, and are not particularly choosy (Small 1988, 1989a). Thus the sociobiological theory that females should be choosy and careful is not clearly borne out by the data, at least for nonhuman primates. The specific data on humans is also confusing. Whyte (1978) found that of 186 cultures, 77.4% considered the male and female sex drive equally as strong. Broude (1980) comments that societies always restrict female sexuality more than male sexuality, but this finding does not mean that w o m e n are less interested in, sex than men, only that they are not allowed to express their sexual desires. Several studies of human sexual practice are informative, however, at least for Euroamerican culture. The first extensive study was conducted by Kinsey and colleagues from 1938 until 1950 (Kinsey et al. 1953;

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Gebhard and Johnson 1979). Their work was based on interviews with 5940 women of all ages, socioeconomic classes, education, and religious backgrounds, but only of Euroarnerican origin. Kinsey and colleagues were interested in the physiological and psychological aspects of h u m a n female sexual response and the changes in those responses with age. This study is quite remarkable for its time; long before the so-called sexual revolution, the female subjects answered questions about orgasms, coital frequency, pre- and extramarital coitus, and masturbation. The findings were, and still are, important in breaking cultural stereotypes about female sexual response. For example, using data on masturbation, Kinsey et al. discovered that h u m a n females reach orgasm as quickly as males and that only the position of the clitoris relative to the vaginal opening makes penile-induced orgasm more difficult for females. A Redbook magazine survey of more than 100,000 women was compiled in 1974 by Tavris and Sadd (1975). The sample includes women from all ages, educational backgrounds, religious beliefs, and political positions. The authors concentrated on a random sample of 18,000 married women, sometimes using only 2278 cases for specific questions. They discovered that, according to these women, more frequent sex translates into a more satisfactory sex life. Of the women who were having sex 11 or more times a month, more than 80% reported that their sex life was satisfactory. Women who had less sex per month were u n h a p p y with their rate of intercourse and their overall sex life. Only 4% of the women thought they were having too much sex. Orgasms, these women claim, are purely a matter of partner technique. Husbands need to learn exactly how to stimulate wives, and then orgasm is easily achieved. Almost half of the wives (44%) said they initiate sex half the time in the relationship, and 80% of these women were satisfied with their sex lives. Seventy-five percent said they took an active part in sexual activity in bed, and only 13% could be classified as truly passive. The eroticism of these women, in contrast to what might be expected from women supposedly uninterested in sex, is quite surprising. For example, six wives out of ten had gone to a pornographic movie, seven out of ten liked erotic clothing, and 75% thought that having sex in various locations was exciting. Although the Redbook study provides reliable data on a large sample of women, and thus adds to a picture of female sexuality in the United States, it is hampered by the fact that the sample was limited to married women. In addition, this report does not have comparative figures for males, unlike the Kinsey study. This information, however, does indicate a reasonably high level of female sexual interest among married women who are under social sanctions to constrain their sexual behavior within a monogamous relationship.

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Hite's (1976) work on female sexuality was less rigorous but is nonetheless informative about more current standards of female sexuality, at least in western cultures. Her sample consists of 3019 w o m e n who responded to a questionnaire. Like the Kinsey sample, these women were not chosen at random, but they are much more geographically diverse and represent numerous socioeconomic classes, levels of education, and ethnic groups. In a sense, the Hite data are even more revealing than the Kinsey data because they represent freer and more elaborate answers from a more diverse population. The striking feature of The Hite Report is the strong, and quite varied, words of the women themselves. Unhampered by histograms and levels of statistical significance, these words literally leap from the pages and define h u m a n female sexuality. The subjective response of the reader is that females are deeply concerned with their sexuality and the pleasure they receive.

PHYSIOLOGY AND WOMEN'S SEXUALITY The uniqueness of female reproductive physiology is the foundation upon which the singular nature of h u m a n female sexuality is constructed. Less tied to the hormonal fluctuations of a strict estrous cycle, human females may be motivated to engage in sexual behavior regardless of their potential for conception. In other words, there seems to be less connection between human female sexual behavior and reproduction than there is among other animals. Orgasm is not necessary for conception, and it can be achieved at any time given proper stimulation. The latter statement is true for males as well, but the former is not. With male orgasm comes ejaculation and the expulsion of gametes. Evolutionary theory suggests that males should be interested in sex at any opportunity because they might have a chance to improve their reproductive success. Thus a major reproductive difference exists between males and females, but this difference in methods of dispensing gametes does not necessarily lead to a difference in sexual motivation. Females, with their potential for orgasm, might also be interested in sex at any opportunity, regardless of the impact of sexual behavior on reproductive success. Evolutionary theorists have assumed that males, with their potential for spreading gametes, are more sexually motivated than females, yet the information on female sexuality demonstrates a certain insatiability for these presumably sexually uninterested females. This insatiability is sufficiently strong, some suggest, that males must restrict female sexuality (Goethals 1971), and in most cultures they do. The evolutionary reason for a high degree of female sexual potential has not been addressed in the literature. If we accept the recent charac-

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terizafion of human females as having a capacity for multiple orgasms, interest in sexual interaction, and continuous attractivity to males, the "new sexual woman" requires some evolutionary explanation. What do females gain from a high rate of sexual interest? There are three possible explanations. First, since ovulation is concealed not only from males but from the females themselves, it behoves them to copulate as often as possible (Small 1988). Although male sperm supplies are relatively easily available, supplies become depleted with repeated ejaculations. Females may need to engage in repeated copulations and in matings with other males merely to conceive. Second, as other authors have suggested (Alexander and Noonan 1979; Lovejoy 1981), the pair bond may be enhanced w h e n males and females engage in frequent bouts of intimacy. Third, if there were no sexual motivation on the part of females, there would be no reason to assume that females would become pregnant. Surely males would be more interested in an active rather than a passive sexual partner. The n o n h u m a n primate literature, especially of the closely related chimpanzees, shows that females initiate most of the copulations by responding to excited males (Goodall 1986; Tutin 1979). Instead of explaining why females should be passive and choosy, the above description of female sexuality begs for continued thoughtful discussion of why female sexuality is so very active and yet suppressed by society.

FEMALE CHOICE

Darwin gave a precise meaning to the phrase "female choice" w h e n he developed sexual selection theory (Darwin 1859, 1871). According to Darwin, female choice, or intersexual selection, can be of evolutionary significance w h e n it explains the evolution of exaggerated male characteristics that appear at puberty in males. The female role in this scenario is presumably as chooser; she mates with a male who carries a particular trait, and that trait is passed on to her sons. Since Darwin's time, another form of "female choice" has been defined by evolutionary biologists (Small and Palombit 1991). Trivers (1972) suggests that females might choose for their own benefit. Since females have limited reproductive potential, and they typically invest so heavily in offspring, they should be careful when choosing a mate. Females might choose males with the best genes, access to important resources, ability to provide (or interest in providing) parental care, high status, or ability to provide other future benefits regardless of the effect of that choice on the characteristics of future offspring (see Small 1989a; Small and Palombit 1991).

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It is difficult to find classic examples of the first kind of "female choice" (i.e., "intersexual selection") among humans; we are not particularly dimorphic in size or morphology. Most traits that appear in males at puberty are primary sexual characteristics (enlarged testes, lengthened penis) or are shared by males and females (e.g., axillary hair). Even facial hair in males, which could be a sexually selected character, exhibits extensive racial variation and thus is not specieswide. This is not to suggest that human females (and males) do not make mate choices-only that these choices may not have an evolutionary effect via sexual selection on the appearance of characteristics that distinguish males from females. There is good evidence, however, that human females make the second kind of "female choice," choice for their own reproductive success. They are interested in resources males can supply, including infant care. Both in western society and in other cultures, females make direct choices for mates or influence family decisions. The impact of female mating strategies, but not necessarily female choice per se, on shaping the evolution of human mating and family systems has been the subject of speculation by anthropologists. Most accounts suggest that females "use" their sexuality to ensure paternal investment (e.g., Alexander and Noonan 1979; Strassmann 1981; Turke 1984) or male resources and reciprocity of goods (e.g., Irons 1983; Lovejoy 1981; see also Fedigan 1986 for a review). In all these scenarios, concealed ovulation and so-called continuous receptivity are the keys to understanding the mating relationship between hominid males and females. They hypothesize that somewhere along the human lineage, selection operated against external displays of estrus. This point is ambiguous for two reasons. First, "concealed ovulation" in humans may be a primitive rather than a derived characteristic (Blaffer Hrdy 1983), and second, there is no clear evidence that ovulation is completely concealed in the human species (see Burley 1979 for a discussion on ovulation and from whom ovulation is supposedly being concealed). In any case, these authors suggest that, along with concealed ovulation, our hominid ancestral females became continuously available for sex, and they used their sexual flexibility in trade for faithful mates, paternal care, and reciprocal goods and services. Females were able to make this trade because they had something males wanted--sex. The biological basis for this trade, manifest as an inexhaustible male urge, is improved reproductive success for males w h o mate with multiple partners and disseminate sperm at every opportunity. Females then could trade their sexual access to males w h o would do anything to mate. There are, however, several major flaws in this line of reasoning. First and foremost, it suggests that for generations, hominid males, w h o

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would do best by mating with multiple females, have been fooled into m on o g amy wh en a female offers herself as one continuous sexual outlet. The evolutionary basis for differences in mating strategies between males and females is, however, for males to mate with multiple partners, not just at a higher rate than females. Monogamy based on male sexual satisfaction with one ever-available female could not easily evolve; there must be other reasons for males to remain with a single mate. Second, there is no clear evidence that males naturally have higher sex drives than females, or that males are more interested than females in matings with other partners. In addition, females, given the opportunity, seem as much interested in multiple partners as males (Johnson 1970). Third, sex may not be the issue at all. Short (1976) suggests that h u m ans are not particularly sexual creatures compared to other primates. Males have small testes and low sperm counts, and females have a long period of adolescent sterility and afterward are usually pregnant or lactating. Most societies also have cultural taboos against sex during much of the year or throughout a lengthy proportion of an individual's life span (Ford and Beach 1951). We like to see ourselves as highly sexual creatures, and un der this assumption, perhaps h u man females could wield their sexuality as a weapon. But the effect of the weapon is only as good as the target; sex as a w eapon may actually have little power in the daily machinations of h u m a n societies. Fourth, those who argue that females need to snare males into providing paternal care by giving them sex overlook the fact that male reproductive success in K-selected species is as d e p e n d e n t on parental care as female success. If a male abandons his offspring, they are likely to die. Thus, females need not coax males to stay and help; selection will do this anyway. Perhaps the most reasonable scenario for h u m a n mate choice and family structure is one that has little to do with sexuality. According to Irons (1983) and Lancaster and Lancaster (1983), the h u m a n mating system probably evolved as one of reciprocity, but without the element of sex. Both parties cooperated to make and raise d e p e n d e n t offspring. Both parties gained sexual satisfaction either within or outside the bond. The data on extramarital affairs in western and other cultures suggest that humans today usually see marriage and sex, spouses and mates, and sex and reproduction as different entities. Is it unreasonable to suggest that our hominid forebears maintained the same dichotomies? FEMALE SEXUALITY AND MATE CHOICE IN WESTERN SOCIETIES Data on female sexual behavior in the United States confirms an active interest of females in sex. Kinsey at al. (1953) report that 50% of the

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females questioned engaged in intercourse before marriage. Of those, 41% had coitus with their fianc6 and with another partner. During marriage, female interest in sex rises and remains steady whereas male interest declines with age. Although Kinsey et al. felt that the rate of sex with different partners for female informants was lower than that for males, females also often engage in sex with different partners. The incidence of extramarital affairs confirms this supposition. Gebhard and Johnson (1979), who reevaluated and added to the Kinsey data, report that 23-56% of the males and 17-25% of the females in their survey had been involved in extramarital affairs. The Kinsey data (Kinsey et al. 1953) and the Hite interviews (Hite 1976) report similar figures for females. Tavris and Sadd (1975) report that 28% of the first-married wives and 35% of remarried wives admitted to extramarital affairs. Johnson (1970) factored "opportunity" into the disparate figures for male and female extramarital affairs. He discovered that males have more opportunities than females (or they perceive more opportunities), and he suggests that if females had similar chances, their rate of affairs would dramatically increase. This possibility is reinforced by the Redbook data, in which twice the number of working w o m e n had extramarital affairs than did housewives (Tavris and Sadd 1975). Although the difference might be explained by a correlation between work and a heightened sex drive for these females, this explanation seems implausible. In fact, the instances of extramarital sex for part-time workers fell in between those for full-time workers and those for full-time housewives. Females usually (and more often than males) cited sexual dissatisfaction or boredom within the marriage as the motivation for "looking elsewhere" (Hunt 1969; Johnson 1970; Tavris and Sadd 1975). More interesting is the effect of these affairs on the marriage. Most often, affairs occur during the first 4 years of marriage, and divorce results in only 1-2% of the cases; in more than 50% of the affairs, the spouses never knew of the infidelity (Gebhard and Johnson 1979). Extrapair matings are not used to disrupt marriages, to produce children with other partners, or to cause divorce (Essock-Vitale and McGuire 1985; Hunt 1969; Tavris and Sadd 1975); for both males and females, they appear to be simple sexual liaisons. In a study of mate choices, Buss (1985) found that people positively assort for age, race, religion, ethnic background, socioeconomic status, and geographic location. Some of these traits, like race and socioeconomic status, are of course highly correlated. He also points out that when couples chose for race they chose for similar physical characteristics. In a questionnaire, Buss (1985) gave individuals a possible list of characteristics they could rate for importance in choosing a mate. The ratings for males and females differed slightly; males ranked physical attractiveness higher than females, and females preferred males with

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financial stability. But the rankings also show the similarity between males and females; both share the same first seven characters, albeit in slightly different order. Essock-Vitale (1984) suggests that preference for male wealth and status by females in western cultures may be an example of truthful advertising by males, since wealthy males sometimes have higher reproductive success. Clearly, females do not mate at random. In sexual relations and in marriage, females have both reproductive and personal reasons for choosing a mate. Often marriages are arranged, but there is no reason to assume that the interests of the females in an arranged marriage are necessarily different from the interests of the families involved (Irons 1983). From an evolutionary standpoint, females should be quite choosy when the chance of pregnancy is high, but outside probable periods of ovulation, sex is as disconnected from reproduction in females as it is in males, perhaps more so since males are always potentially fertile whereas females are only fertile for a restricted time. Buss (1986) suggests that human females need not attend to cues of male reproductive value, since male value (sperm viability) reduces only slightly with age. What "should" be important to females w h e n they are considering reproduction is paternal care and resources necessary for long periods of human infant dependence. The difficulty for females is in assessing male care when males have no history of parenting. Resources are easier to evaluate; females can assess status, goods, and financial stability, all of which might aid in offspring longevity. Choices for marriage partners imply choices for fathers and for an economic union. Females also engage in sex outside marriage, but the variables that lead to a particular choice in a nonmarital, usually nonreproductive, sexual partner have yet to be investigated.

FEMALE SEXUALITY AND MATE CHOICE IN OTHER CULTURES Female mate choices in all cultures are compromised by male power. Male power, in turn, is wielded to control female reproduction. As Blaffer Hrdy (1981) suggests, males would not need to sequester females if females were sexually passive. In other words, female sexual interest puts females at risk for male domination. Almost universally, social and physical restrictions are harsher on females than on males (Gebhard 1971). Females are often married early and kept away from opportunities for premarital matings (Rosenblatt and Anderson 1981). But even in arranged situations, females may have influence. Using literature from the H u m a n Relations Area File (HRAF), I evalu-

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ated nonwestern societies in terms of female mating and marriage patterns. I used the Standard Cross-Cultural Sample (Murdock and White 1969), which consists of societies from all geographic areas and representing most subsistence types (hunter-gatherers, horticulturists, etc.). I was interested in determining if females in most cultures have any say in choosing marriage partners, and once marriage occurs, if females mate with males other than their husbands. In other words, do w o m e n exert choice in marriage and mating? Evolutionary theory predicts that females will be choosy, exclusive, and not interested in sex with different partners. This theory also predicts that males will be concerned with keeping the reproductive potential of their wives to themselves. My evaluation of the data was designed as a test of those predictions. Two subject areas were considered, marriage arrangements and extramarital affairs. I asked the following questions: Are the marriages arranged? When marriages are arranged, do females have a voice in the acceptance or rejection of the proposed partner? Are some marriages not arranged? Do females engage in extramarital affairs, and when they do, are these affairs socially acceptable? Does divorce result from female infidelity? And finally, do males offer their wives to other males? A marriage was considered arranged from the female's point of view when parents, the groom alone, relatives, or any individuals other than the bride made the decision. When two separate accounts provided different information, both were included in the analysis. For example, if one ethnographer said arranged marriages were standard and another ethnographer stated marriages were not arranged, the culture was scored as having both types of marriage. Information on marriage and extramarital sex is available for 133 groups. Arranged marriages were found in 106 societies (80%), but surprisingly, only 23 (17%) exhibit arranged marriages exclusively. Almost all groups that exhibit arranged marriages also accept unarranged marriages (83; 78%). The main difference between the two types of marriage, as defined here, is the amount of influence both partners might have on mate choice. In arranged marriages, families decide and do not consult the partners or ignore the partners' wishes. In unarranged marriages, the families are not involved until after the choices have been declared. Whyte (1978) reports that when the bride and groom are allowed a voice in arrangements, males and females have an equal say in the arrangements of marriage in 57.5% of the groups he evaluated (186 groups from the Standard Cross-Cultural Sample). Males do have some advantage according to Whyte, since the groom has a strong to slight influence in 38.8% of the cultures whereas the bride has more influence only in 3.8% of the groups. We cannot assume, however, that the

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interests of the family and of the bride and groom are different, or that the bride has no influence over her family. Females have a voice in arranged marriages (i.e., are able to reject offers) in 43 (60%) of the 106 societies that have arranged marriages. Thus, "arranged" does not necessarily mean the woman is forced or coerced. According to evolutionary theory (Betzig 1988; Trivers .1972), brides "should" be interested in gaining mates of high status and resources, and the family is interested in the same (see Vining 1986 for a discussion of this issue). Most cultures clearly differentiate between marriage and sexual matings, and it is marriage, rather than sexual mating, that is important to all human cultures (Rosenblatt and Anderson 1981). Although sexual liaisons might result in offspring, marriages are long-term and involve exchanges of goods, land, and political alliances. This notion is supported by the lack of voice for females in arranged marriages in infancy and childhood; these females do not have a voice because the proposed marriage is a political or economic union, not a love match. These childhood engagements are often broken in adulthood (25% of young betrothals can be broken when the female becomes of age.) Females have other ways to influence or escape arranged marriages. Since elopement and divorce occur in most of these cultures, females may not be helpless when parents override their daughter's choices. Perhaps most females who are under stiff restrictions to accept arranged marriages do not protest because they really do not care w h o they marry, and they assume that their families have their best interests in mind. In addition, since some females in all societies exhibit infidelity, females need not look on an arranged marriage as the end of love. In many of the arranged marriages, the topic of female choice was not a focus of attention because the ethnographer did not investigate the power of the bride's opinion, especially when that opinion may have been voiced behind closed doors. In addition, in most strictly arranged marriages the groom was also subject to the same familial strongarming. We cannot assume that an arranged marriage is more unsatisfying sexually or emotionally than an unarranged marriage. Rosenblatt and Anderson (1981) suggest that a strong premarital fantasy life might heighten attraction and attachment in arranged marriages. In addition, ceremonial trappings elevate the relationship past that of a simple arrangement. At the same time, there is less pressure for compatibility (Rosenblatt and Anderson 1981). Freedom of choice may, in fact, be a less desirable option (Rosenblatt and Cozby 1972); with freedom of choice comes choice for impractical, often transitory traits, such as love and sexual attraction. In addition, "freedom" is relative, since opportunities for "falling in love" are b o u n d e d by cultural opportunities that

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usually throw appropriate, culturally sanctioned individuals together. All cultures also have rules of exogamy that dictate social and familial norms and limit even the freest of choices. Even in "free" marriages, parental approval is almost always sought. Often, a marriage considered to be arranged was in fact perpetrated by the couple involved and is labeled an unarranged marriage in this analysis. In some cases, the male was given a choice but the female was not (scored with a "no" in the category for female voice in unarranged marriages). A total of 108 (81%) of the societies exhibit unarranged marriages. Only rarely (in just three societies) do males have freedom to choose while females must accept male choice. Cross-culturally, highstatus males in traditional societies often have more wives and more children than lower-status men, and wives often choose to be in polygynous marriages (Betzig 1986; Borgerhoff Mulder 1990, 1992; Flinn 1986; Irons 1979, 1980; Turke and Betzig 1985; but see Borgerhoff Mulder 1989). In addition, high-status females also have higher fertility and a higher rate of survival for their infants than lower-status w o m e n (Irons 1979, 1980). Although one might hypothesize that females would choose to mate in a polygynous rather than monogamous fashion if this choice improved female reproductive success or infant survival, the data on lifetime reproductive success of polygynous females is unclear (Borgerhoff Mulder 1990). H y p e r g y n y (when lower-status females marry higher-status males) is found in many cultures that exhibit a correlation between male status and male reproductive success (Dickernann 1979). In the 133 societies evaluated, at least some females in all cultures engage in extramarital affairs. Most of the societies for which there was information (n = 100) express disapproval for both males and females. In only 38 (38%) were affairs acceptable and expected for women. Mention of male infidelity never occurred without female infidelity. Surprisingly, several groups noted that children born from extra-pair matings were considered the responsibility of husbands (as they are in the U.S. legal system). For example, husbands in the Masai, Teda, Toda, and other cultures welcome "illegitimate" children as their own. Presumably children in these societies are considered an added benefit rather than a burden. On the other hand, perhaps fathers invest less in their nonbiological children than in their own progeny, as Daly and Wilson (1988) have demonstrated. Whyte (1978) and Broude and Greene (1976) also found that extramarital affairs by males and females were present in most cultures. Broude and Greene (1976) report that males in 80% of the cultures and females in 73% of the cultures engage in extramarital liaisons. A double standard seems to exist in most cultures. Extramarital affairs are allowed, or simply ignored, for males, whereas the punishment for fe-

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males is often severe. In Whyte's sample of 186 societies, a double standard was found in 42.7%, and where there is evidence of a double standard, females are punished more often than males. Broude and Greene (1976) provide similar results, with a double standard appearing in 43.1% of the 200 cultures they surveyed. Broude (1980) comments that extramarital sex worldwide is condoned for the husband and condemned for the wife. She comments, however, that this finding does not indicate that females are less interested than males. On the contrary, Broude suggests that women are restricted because men are frightened of the reproductive and sexual potential of women. She further points out that when women are allowed to participate in sexual behavior with men who are not their husbands, this behavior is still often controlled by husbands. In other words, when husbands "allow" female infidelity, they usually gain in the arrangement. For example, wife exchange establishes and reinforces reciprocal altruism and alliances among men; fraternal polyandry potentially increases a husband's inclusive fitness; and in some cases a male might receive compensation from his wife's lover (Broude 1980). Information on wife sharing was found in 32 of the societies examined here. Twenty-four groups (75%) either stated that husbands regularly, and without jealousy, "gave" their wives to other men, or they made no mention of sharing. Presumably the latter groups should be included with the " n o " rather than the "yes" groups. In any case, w h e n wife sharing occurs, females are not necessarily pawns in this hospitality game because their approval or agreement is usually necessary. Almost universally, adulterous females are punished, or disapproved of, more than males. Punishment ranges from malicious gossip and social ostracism to physical abuse and death. In 20% of 186 societies evaluated by Broude and Greene (1976), extramarital sex was condemned for both males and females; 12% stated that affairs were acceptable for both sexes, and 43% noted that affairs were acceptable for males but not females. Seventy-three percent of the societies said married females have affairs, and 80% of the societies stated males have affairs (Broude and Greene 1976). My reading of the ethnographies only differs in that extramarital affairs were noted for males and females in all societies, although for a few societies only infrequent infidelity was reported for both males and females. Regardless of approval or disapproval, the rate of extramarital sex was almost equal for males and females (cf. Broude and Greene 1976). Rosenblatt and Anderson (1971) suggest that the "double standard" is really a statement about the power to control (or about attempts to control) rather than differences in male and female sexuality. Although divorce occurs in almost all societies (77.4% in Whyte's 1978

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sample), infidelity is rarely a cause for divorce (only in 28 of 70 groups for which data were available). In 36%, no divorce resulted; at the other extreme, in 9% men killed their adulterous wives. Most often, however, couples come to terms with the infidelity and move on, as the data from western cultures also show. Presumably the maintenance of the economic and political family unit is more important than sexual exclusivity. A few groups believe that female infidelity affects the health of her mate; husbands become physically ill from a unfaithful wife. Thus the disapproval is manifest not in punishment or abandonment but in guilt that presumably has a preventative effect. CONCLUSION There are certain inherent flexibilities in h u m a n mating strategies that refect physiological and social abilities and constraints. Males are able to fertilize several females, but their powers of insemination are not exhaustive. Females mate throughout their cycles and nonseasonally, and ovulation is somewhat concealed. But similar constraints on males and females delimit h u m a n reproduction and mold mating strategies to a compromise. Lacking flamboyant advertisement of fertility, neither females nor males are able to pinpoint ovulation and control reproduction. Females are restrained in their reproductive output by dependent offspring. Males too are constrained by the slow development of the human infant, that packet of reproductive success that evolution has pushed to the extreme of dependency. Although the details of h u m a n sexuality clearly show differences in male and female sexual response and actions, the similarities are also striking. Females respond to arousal as quickly as males; females are just as interested in sexual satisfaction as males; and given the proper partner, females will enjoy sex as much as males. Across cultures, females engage in extramarital affairs almost as often as males, or they wish they could, even though most societies disapprove of this behavior. Both males and females play the mate choice game, presumably to improve reproductive success, and both must bow to the wishes of families and operate under the rules of society. In this sense, no mate choices and no sexual acts are really "free." At a fundamental level, h u m a n s are driven by the biological urge to enjoy the pleasures of the body. Sexual behavior also happens to result in offspring. The passage of genes, the establishment of alliances, and the need for economic security are concerns not just of the mating pair, but also of the larger familial gene pool. I thank Ute van den Bergh and Tim Merrick for helpful discussion about human sexuality.

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Meredith F. Small is associate professor of anthropology at Cornell University. For the past 14 years she has studied reproductive biology and mating behavior in three species of macaques. Most recently, she worked with captive Barbary macaques (Macaca sylvanus), reportedly the most promiscuous primate. Her most recent articles include "Promiscuity in Barbary Macaques" (AmericanJournalof Primatology20:267-282, 1990), and "Alloparental Behavior in Barbary Macaques" (Animal Behavior39:297-306, 1990). She is currently working on a book on female choice for Cornell University Press.

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Tavris, C., and S. Sadd 1975 The Redbook Report on Female Sexuality. New York: Delacorte Press. Trivers, R. L. 1972 Parental Investment and Sexual Selection. In Sexual Selection and the Descent of Man, B. Campbell, ed. Pp. 1136-1179. Chicago: Aldine. Turke, P. W. 1984 Effects of Ovulatory Concealment and Synchrony of Protohominid Mating Systems and Parental Roles. Ethology and Sociobiology 5:33 44. Turke, P. W., and L. L. Betzig 1985 Those Who Can, Do: Wealth, Status and Reproduction on Ifaluk. Ethology and Sociobiology 6:79-87. Tutin, C. 1979 Mating Patterns and Reproductive Strategies in a Community of Wild Chimpanzees (Pan troglodytes schweinfurthii). Behavioral Ecology and Sociobiology 6:29-38. Udry, J. B., N. M. Morris, and L. Walker 1973 Effect of Contraceptive Pills on Sexual Activity in the Luteal Phase of the Human Menstrual Cycle. Archives of Sexual Behavior 2:205-214. Veith, J. L., M. Buck, S. Getzlaf, P. Van Dalfsen, and S. Slade 1983 Exposure to Men Influences the Occurrence of Ovulation in Women. Physiology and Behavior 31:313-315. Vining, D. R. 1986 Social versus Reproductive Success: The Central Theoretical Problem of Human Sociobiology. Brain and Behavioral Sciences 9:167-216. Whyte, M. K. 1978 Cross-cultural Codes Dealing with the Relative Status of Women. Ethnology 17:211-237. Wolfe, L. D. 1991 Human Evolution and the Sexual Behavior of Female Primates. In Understanding Behavior, J. D. Loy and C. B. Peters, eds. Pp. 121-151. Oxford: Oxford University Press.

The evolution of female sexuality and mate selection in humans.

Understanding female sexuality and mate choice is central to evolutionary scenarios of human social systems. Studies of female sexuality conducted by ...
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