The Evolution of Human Sexuality by Donald Symons (Oxford University Press 1980).
Research over the last four decades in the field that has come to be known as evolutionary psychology has focused disproportionately on mating behaviour. Geoffrey Miller (1998) has even argued that it is the theory of sexual selection rather than that of natural selection which, in practice, guides most research in this field.
This does not reflect merely the prurience of researchers. Rather, given that reproductive success is the ultimate currency of natural selection, mating behaviour is, perhaps along with parental investment, the form of behaviour most directly subject to selective pressures.
Almost all of this research traces its ancestry ultimately to Donald Symons’ ‘The Evolution of Human Sexuality’ by Donald Symons. Indeed, much of it was explicitly designed to test claims and predictions formulated by Symons himself in this very book.
For example, in his discussion of the age at which women are perceived as most attractive by males, Symons formulated two alternative hypotheses.
First, if human evolutionary history were characterized by fleeting one-off sexual encounters (i.e. one-night stands, casual sex and hook-ups), then, he reasoned, men would have evolved to find women most attractive when the latter are at the age of their maximum fertility.
For women, fertility is said to peak around when a woman reaches her mid-twenties since, although women still in their teens have high pregnancy rates, they also experience greater risk of birth complications.
However, if human evolutionary history were characterized instead by long-term pair bonds, then men would have evolved to be maximally attracted to somewhat younger women (i.e. those at the beginning of their reproductive careers), so that, by entering a long-term relationship with the woman at this time, a male is potentially able to monopolize her entire lifetime reproductive output (p189).
More specifically, males would have evolved to prefer females, not of maximal fertility, but rather of maximal reproductive value, a term borrowed from demography and population genetics which refers to a person’s expected future reproductive output given their current age. Unlike fertility, a woman’s reproductive value peaks around her mid- to late-teens.
On the basis of largely anecdotal evidence, Symons concludes that human males have evolved to be most attracted to females of maximal reproductive value rather than maximal fertility.
Subsequent research designed to test between Symons’s rival hypotheses has largely confirmed his speculative hunch that it is younger females in their mid- to late-teens who are perceived by males as most attractive (e.g. Kenrick and Keefe 1992).
Why Average is Attractive
Symons is also credited as the first person to recognize that a major criterion of attractiveness is, paradoxically, averageness, or at least the first to recognize the significance of, and possible evolutionary explanation for, this discovery. Thus, Symons argues that:
“[Although] health and status are unusual in that there is no such thing as being too healthy or too high ranking… with respect to most anatomical traits, natural selection produces the population mean” (p194).
Support has even emerged for some of Symons’ more speculative hunches.
For example, one of Symons’ two proposed scenarios for the evolution of concealed ovulation, in which he professed “little confidence” (p141), was that this had evolved so as to impede male mate-guarding and enable females select a biological father for their offspring different from their husbands (p139-141).
Consistent with this theory, studies have found that women’s mate preferences vary throughout their menstrual cycle in a manner compatible with a so-called ‘dual mating strategy’, preferring males evidencing a willingness to invest in offspring at most times, but, when at their most fertile, preferring characteristics indicative of genetic quality (e.g. Penton-Voak et al 1999).
Meanwhile, a questionnaire distributed via a women’s magazine found that women engaged in extra-marital affairs do indeed report engaging in ‘extra-pair copulations’ (EPCs) at times likely to coincide with ovulation (Bellis and Baker 1990).
The Myth of Female Choice
Interestingly, Symons even anticipated some of the mistakes evolutionary psychologists would be led into.
Thus, he warns that researchers in modern western societies may be prone to overestimate the importance of female choice as a factor in human evolution, because, in their own societies, this is a major factor, if not the major factor, in determining marriage and sexual and romantic relationships (p203).
However, in ancestral environments (i.e. what evolutionary psychologists now call the Environment of Evolutionary Adaptedness or EEA) arranged marriages were likely the norm, as they are in most premodern cultures around the world today (p168).
Thus, Symons concludes:
“There is no evidence that any features of human anatomy were produced by intersexual selection [i.e. female choice]. Human physical sex differences are explained most parsimoniously as the outcome of intrasexual selection (the result of male-male competition)” (p203).
Thus, human males have no obvious analogue of the peacock’s tail, but they do have substantially greater levels of upper-body strength and violent aggression as compared to females.
This was a warning almost entirely ignored by subsequent generations of researchers before being forcefully reiterated by Puts (2010).
Homosexuality as a ‘Test-Case’
An idea of the importance of Symons’s work can be ascertained by comparing it with contemporaneous works addressing the same subject-matter.
However, whereas Symons’s book set out much of the theoretical basis for what would become the modern science of evolutionary psychology, Wilson’s chapter on “Sex” has dated rather less well, and a large portion of chapter is devoted to introducing a now faintly embarrassing theory of the evolution of homosexuality which has subsequently received no empirical support (see Bobrow & Bailey 2001).
In contrast, Symons’s own treatment of homosexuality is innovative. It is also characteristic of his whole approach and illustrates why ‘The Evolution of Human Sexuality‘ has been described by David Buss as “the first major treatise on evolutionary psychology proper” (Handbook of Evolutionary Psychology: p251).
Rather than viewing all behaviours as necessarily adaptive (as critics of evolutionary psychology, such as Stephen Jay Gould, have often accused sociobiologists of doing), Symons instead focuses on admittedly non-adaptive (or, indeed, even maladaptive) behaviours, not because he believes them to be adaptive, but rather because they provide a unique window on the nature of human sexuality.
Accordingly, Symons does not concern himself with how homosexuality evolved, implicitly viewing it as a rare and maladaptive malfunctioning of normal sexuality. Yet the behaviour of homosexuals is of interest to Symons because it provides a window on the nature of male and female sexuality as it manifests itself when freed from the constraints imposed by the conflicting desires of the opposite sex.
On this view, the rampant promiscuity manifested by many homosexual men (e.g. ‘cruising’ and ‘cottaging’ in bathhouses and public lavatories, or Grindr hookups) reflects the universal male desire for sexual variety when freed from the constraints imposed by the conflicting desires of women.
This desire for sexual variety is, of course, obviously reproductively unproductive among homosexual men themselves. However, it evolved because it enhanced the reproductive success of heterosexual men by motivating them to attempt to mate with multiple females and thereby father multiple offspring.
In contrast, burdened with pregnancy and lactation, women’s potential reproductive rate is more tightly constrained than that of men. They therefore have little to gain reproductively by mating with multiple males, since they can usually gestate, and nurse, only one offspring at a time.
It is therefore notable that, among lesbians, there is little evidence of the sort of rampant promiscuity common among gay men. Instead, lesbian relationships seem to be characterized by much the same features as heterosexual coupling (i.e. long-term pair-bonds).
The similarity of heterosexual coupling to that of lesbians, and the striking contrast with that of male homosexuals, suggests that it is women, not men, who exert decisive influence in dictating the terms of heterosexual coupling.
Thus, Symons reports:
“There is enormous cross-cultural variation in sexual customs and laws and the extent of male control, yet nowhere in the world do heterosexual relations begin to approximate those typical of homosexual men… This suggests that, in addition to custom and law, heterosexual relations are structured to a substantial degree by the nature and interests of the human female” (p300).
This conclusion is, of course, diametrically opposite to the feminist contention that it is men who dictate the terms of heterosexual coupling and for whose exclusive benefit such relationships are structured.
It also suggests, again contrary to feminist assumptions of male dominance, that most men are ultimately frustrated in achieving their sexual ambitions to a far greater extent than are most women.
Thus, Symons concludes:
“The desire for sexual variety dooms most human males to a lifetime of unfulfilled longing” (p228).
Here, Symons anticipates Camille Paglia who was later to famously observe:
“Men know they are sexual exiles. They wander the earth seeking satisfaction, craving and despising, never content. There is nothing in that anguished motion for women to envy” (Sexual Personae: p19).
Criticisms of Symons’s Use of Homosexuality as a Test-Case
There is, however, a potential problem with Symons’s use of homosexual behaviour as a window onto the nature of male and female sexuality as they manifest themselves when freed from the conflicting desires of the opposite sex. The whole analysis rests on a questionable premise – namely that homosexuals are, their preference for same-sex partners aside, otherwise similar, if not identical, to heterosexuals of their own sex in their psychology and sexuality.
Symons defends this assumption, arguing:
“There is no reason to suppose that homosexuals differ systematically from heterosexuals in any way other than their sexual object choice” (p292).
Indeed, in some respects, Symons seems to see even “sexual object choice” as analogous among homosexuals and heterosexuals of the same sex.
For example, he observes that, unlike women, both homosexual and heterosexual men tend to evaluate prospective mates primarily on the basis their physical appearance and youthfulness (p295).
Thus, in contrast to the failure of periodicals featuring male nudes to attract a substantial female audience (see below), Symons notes the existence of a market for gay pornography parallel in most respects to heterosexual porn – i.e. featuring young, physically attractive models in various states of undress (p301).
This, of course, contradicts the feminist notion that men are led to ‘objectify’ women only due to the sexualized portrayal of the latter in the media.
Instead, Symons concludes:
“That homosexual men are at least as likely as heterosexual men to be interested in pornography, cosmetic qualities and youth seems to me to imply that these interests are no more the result of advertising than adultery and alcohol consumption are the result of country and western music” (p304).
However, this assumption of the fundamental similarity of heterosexual and homosexual male psychology has been challenged by David Buller in his book, Adapting Minds: Evolutionary Psychology and the Persistent Quest for Human Nature.
Buller cites evidence that male homosexuals are ‘feminized’ in many aspects of their behaviour.
For example, one interesting recent study found that male homosexuals have more female-typical occupation interests than do heterosexual males (Ellis & Ratnasingam 2012).
Moreover, one of the few consistent early correlates of homosexuality is gender non-conformity in childhood and some evidence (e.g. digit ratios, the fraternal birth order effect) has been interpreted to suggest that the level of prenatal exposure to masculinizing androgens (e.g. testosterone) in utero affects sexual orientation (see Born Gay: The Pyschobiology of Sexual Orientation).
Indeed, Symons himself mentions the evidence of an association between homosexuality and levels of masculinizing androgens in utero (albeit in respect of lesbians rather than of male homosexuality) just a few pages before his discussion of the promiscuous behaviours of male homosexuals (p289).
As Buller also notes, although gay men seem, like heterosexual men, to prefer youthful sexual partners, they also appear to prefer sexual partners who are, in other respects highly masculine.
Thus, Buller observes:
“The males featured in gay men’s magazines embody very masculine, muscular physiques, not pseudo-feminine physiques” (Adapting Minds: p227).
Indeed, the models in such magazines seem in most respects similar in physical appearance to the male models, pop stars, actors and other ‘sex symbols’ and celebrities fantasized about by heterosexual women and girls.
How then are we to resolve this apparent paradox?
One possible explanation that some aspects of the psychology of male homosexuals are feminized but not others – perhaps because different parts of the brain are formed at different stages of prenatal development, at which stages the levels of masculinizing androgens in the womb may vary.
Indeed, there is even some evidence that homosexual males may be hyper-masculinized in some aspects of their physiology.
For example, it has been found that homosexual males report larger penis-sizes than heterosexual men (Bogaert & Hershberger 1999).
This, researchers Glenn Wilson and Qazi Rahman propose, may be because:
“If it is supposed that the barriers against androgens with respect to certain brain structures (notably those concerned with homosexuality) lead to increased secretion in an effort to break through, or some sort of accumulation elsewhere… then there may be excess testosterone left in other departments” (Born Gay: The Psychobiology of Sex Orientation: p80).
Another possibility is that male homosexuals actually lie midway between heterosexual men and women in their degree of masculinization.
On this view, homosexual men come across as relatively feminine only because we naturally tend to compare them to other men (i.e. heterosexual men). However, as compared to women, they may be relatively masculine, as reflected in the male-typical aspects of their sexuality focused upon by Symons.
Interestingly, this latter interpretation suggests the slightly disturbing possibility that, freed from the restraints imposed by women, heterosexual men would be even more indiscriminately promiscuous than their homosexual counterparts.
Evidence consistent with this interpretation is provided by one study from the 1980s which found that, when approached by a female stranger (also a student), on a University campus, with a request to go to bed with them, fully 72% of male students agreed (Clark and Hatfield 1989).
In contrast, in the same study, not a single one of the 96 females approached by male strangers with the same request on the same university campus agreed to go to bed with the male stranger.
Yet what percentage of the female students subsequently sued the university for sexual harassment was not reported.
Pornography as a “Natural Experiment”
For Symons, fantasy represents another window onto sexual and romantic desires. Like homosexuality, fantasy is, by its very nature, unconstrained by the conflicting desires of the opposite sex (or indeed by anything other than the imagination of the fantasist).
Symons later collaborated in an investigation into sexual fantasy by means of a questionnaire (Ellis and Symons 1990).
However, in the present work, he investigates fantasy indirectly by focusing on what he calls “the natural experiment of commercial periodical publishing” – i.e. pornographic magazines (p182).
In many respects, this approach is preferable to a survey because, even in an anonymous questionnaire, individuals may be less than honest when dealing with a sensitive topic such as their sexual fantasies. On the other hand, they are unlikely to regularly spend money on a magazine unless they are genuinely attracted by its contents.
Before the internet age, softcore pornographic magazines, largely featuring female nudes, commanded sizeable circulations. However, their readership (if indeed ‘readership’ is the right words, since there was typically little reading involved, save of the ‘one-handed‘ variety) was almost exclusively male.
In contrast, there was little or no female audience for magazines containing pictures of naked males. Instead, magazines marketed towards women (e.g. fashion magazines) contain, mostly, pictures of other women.
Indeed, when, in the 1970s, attempts were made, in the misguided name of feminism and ‘women’s liberation’, to market magazines featuring male nudes to a female readership, one such title, Viva, abandoned publishing male nudes after just a few years due to lack of interest or demand, then subsequently went bust just a few years after that, while the other, Playgirl, although it did not entirely abandon male nudes, was notorious, as a consequence, for attracting a readership composed in large part of homosexual men.
Symons thus concludes forcefully and persuasively:
“The notion must be abandoned that women are simply repressed men waiting to be liberated” (p183).
Indeed, though it has been loudly and enthusiastically co-opted by feminists, this view of women, and of female sexuality – namely women as “repressed men waiting to be liberated” – represents an obviously quintessentially male viewpoint.
Indeed, taken to extremes, it has even been used as a justification for rape.
Thus, the curious, sub-Freudian notion that female rape victims actually secretly enjoy being raped seems to rest ultimately on the assumption that female sexuality is fundamentally the same as that of men (i.e. indiscriminately enjoying of promiscuous sex) and that it is only women’s alleged sexual ‘repression’ that prevents them admitting as much.
Unfortunately, however, there is notable omission in Symons’s discussion of pornography as a window into male sexuality – namely, he omits to consider whether there exists any parallel artistic genre that offers equivalent insight into the female psyche.
Later writers on the topic have argued that romance novels (e.g. Mills and Boon, Jane Austin), whose audience is as overwhelmingly female as pornography’s is male, represent the female equivalent of pornography, and that analysis of the the content of such works provides insights into female mate preferences parallel to those provided into male psychology by pornography (e.g. Kruger et al 2003; Salmon 2004; see also Warrior Lovers: Erotic Fiction, Evolution and Female Sexuality, co-authored by Symons himself).
Symons touches upon this analogy only in passing, when he observes that:
“Heterosexual men are, of course, aware that the female sexuality portrayed in men’s magazines reflects male fantasy more than female reality, just as homosexual women are aware that the happy endings of stories in romance magazines exist largely in the realm of fantasy” (p29).
Female Orgasm as Non-Adaptive
An entire chapter of ‘The Evolution of Human Sexuality’, namely Chapter Three (entitled, “The Female Orgasm: Adaptation or Artefact”), is devoted to rejecting the claim that the female orgasm represents a biological adaptation.
This is perhaps excessive. However, it does at least conveniently contradicts the claim of some critics of evolutionary psychology, and of sociobiology, such as Stephen Jay Gould that the field is ‘ultra-Darwinian’ or ‘hyper-adaptionist’ and committed to the misguided notion that all traits are necessarily adaptive.
In contrast, Symons champions the thesis that the female capacity for orgasm is a simply non-adaptive by-product of the male capacity to orgasm, the latter of which is of course adaptive.
On this view, the female orgasm (and clitoris) is, in effect, the female equivalent of male nipples (only more fun).
Certainly, Symons convincingly critiques the romantic notion, popularized by Desmond Morris among others, that the female orgasm functions as a mechanism designed to enhance ‘pair-bonding’ between couples.
However, subsequent generations of evolutionary psychologists have developed less naïve models of the adaptive function of female orgasm.
For example, Geoffrey Miller argues that the female orgasm, and clitoris, functions as an adaptation for mate choice (The Mating Mind: p239-241).
Of course, at first glance, experiencing orgasm during coitus may appear to be a bit late for mate choice, since, by the time coitus has occurred, the choice in question has already been made. However, given that, among humans, most sexual intercourse is non-reproductive (i.e. does not result in conception), the theory is not altogether implausible.
On this view, the very factors which Symons views as suggesting female orgasm is non-adaptive – such as the relative difficultly of stimulating female orgasm during ordinary vaginal sex – are positive evidence for its adaptive function in carefully discriminating between suitors/lovers to determine their desirability as father for a woman ’s offspring.
Nevertheless, at least according to the stringent criteria set out by George C Williams in his classic Adaptation and Natural Selection, as well as the more general principle of parsimony (also known as Occam’s Razor), the case for female orgasm as an adaptation remains unproven (see also Sherman 1989; Case Of The Female Orgasm: Bias in the Science of Evolution).
Much of Symons’ work is dedicated to challenging the naïve group-selectionism of Sixties ethologists, especially Desmond Morris. Although scientifically now largely obsolete, Morris’s work still retains a certain popular resonance and therefore this aspect of Symons’s work is not entirely devoid of contemporary relevance.
In place of Morris‘s rather idyllic notion that humans are a naturally monogamous ‘pair-bonding’ species, Symons advocates instead an approach rooted in the individual-level (or even gene-level) selection championed Richard Dawkins in The Selfish Gene (reviewed here).
This leads to some decidedly cynical conclusions regarding the true nature of sexual and romantic relations among humans.
For example, Symons argues that it is adaptive for men to be less sexually attracted to their wives than they are to other women – because they are themselves liable to bear the cost of raising offspring born to their wives but not those born to other women with whom they mate (e.g. those mated to other males).
Another cynical conclusion is that the primary emotion underlying the institution of marriage, both cross-culturally and in our own society, is neither love nor even lust, but rather male sexual jealousy and proprietariness (p123).
Marriage, then, is an institution borne not of love, but of male sexual jealousy and the behaviour known to biologists as mate-guarding.
Meanwhile, in his excellent chapter on ‘Copulation as a Female Service’ (Chapter Eight), Symons suggests that many aspects of heterosexual romantic relationships may be analogous to prostitution.
As well as its excessive focus on debunking sixties ethologists like Morris, ‘The Evolution of Human Sexuality’ is also out-of-date in a more serious respect Namely, it fails to incorporate the vast amount of empirical research on human sexuality from a sociobiological perspective which has been conducted since the first publication of his work.
For a book first published thirty years ago, this is inevitable – not least because much of this empirical research was inspired by Symons’ own ideas and specifically designed to test theories formulated in this very work.
In addition, potentially important new factors in human reproductive behaviour that even Symons did not foresee have been identified, for example role of levels of fluctuating asymmetry functioning as a criterion for, or at least correlate of, physical attractiveness.
For an updated discussion of the evolutionary psychology of human sexual behaviour, complete with the latest empirical data, readers should consult the latest edition of David Buss’s The Evolution Of Desire: Strategies of Human Mating.
In contrast, in support of his theories Symons relies largely on classical literary insight, anecdote and, most importantly, a review of the ethnographic record.
However, this latter focus ensures that, in some respects, the work remains of more than merely of historical interest.
After all, one of the more legitimate criticisms levelled against recent research in evolutionary psychology is that it is insufficiently cross-cultural and, with several notable exceptions (e.g. Buss 1989), relies excessively on research conducted among convenience samples of students at western universities.
Given costs and practicalities, this is inevitable. However, for a field that aspires to understand a human nature presumed to be universal, such a method of sampling is highly problematic.
‘The Evolution of Human Sexuality’ therefore retains its importance for two reasons.
First, is it the founding work of modern evolutionary psychological research into human sexual behaviour, and hence of importance as a landmark and classic text in the field, as well as in the history of science more generally.
Second, it also remains of value to this day for the cross-cultural and ethnographic evidence it marshals in support of its conclusions.
 Actually, the first person to discover this, albeit inadvertently, was the great Victorian polymath, pioneering statistician and infamous eugenicist Francis Galton, who, attempting to discover abnormal facial features possessed by the criminal class, succeeded in morphing the faces of multiple convicted criminals. The result was, presumably to his surprise, an extremely attractive facial composite, since all the various minor deformities of the many convicted criminals whose faces he morphed actually balanced one another out to produce a face with few if any abnormalities or disproportionate features.
 However, recent meta-analyses have called into question the evidence for cyclical fluctuations in female mate preferences (Wood et al 2014; cf. Gildersleeve et al 2014), and it has been suggested that such findings may represent casualties of the so-called replication crisis in psychology. It has also been questioned whether ovulation in humans is indeed concealed, or is actually detectable by subtle cues (e.g. Miller et al 2007), for example, changes in face shape (Oberzaucher et al 2012), breast symmetry (Scutt & Manning 1996) and body scent (Havlicek et al 2006).
 Another factor leading recent researchers to overestimate the importance of female choice in human evolution is their feminist orientation, since female choice gives women an important role in human evolution, even, paradoxically, in the evolution of male traits.
 Actually, in most cultures, only a girl’s first marriage is arranged on her behalf by her parents. Second- and third-marriages are usually negotiated by the woman herself. However, since female fertility peaks early, it is a girl’s first marriage that is usually of the most reproductive, and hence Darwinian, significance.
 Indeed, the human anatomical trait in humans that perhaps shows the most evidence of being a product of intersexual selection is a female one, namely the female breasts, since the latter are, unlike the mammary glands of most other mammals, permanently present from puberty on, not only during lactation, and composed primarily of fatty tissues, not milk (Møller 1995; Manning et al 1997; Havlíček et al 2016.
 Wilson terms his theory “the kin selection theory hypothesis of the origin of homosexuality” (p145). However, a better description might be the ‘helper at the nest theory of homosexuality’, the basic idea being that, like sterile castes in some insects, and like older siblings in some bird species where new nest sites are unavailable, homosexuals, rather than reproducing themselves, direct their energies towards assisting their collateral kin in successfully raising, and provisioning, their own offspring (p143-7). The main problem with this theory is that there is no evidence that homosexuals do indeed devote any greater energies towards assisting their kin in this respect. On the contrary, homosexuals instead seem to devote much of their time and resources towards their own sex life, much as do heterosexuals (Bobrow & Bailey 2001).
 As we will see, contrary to the stereotype of evolutionary psychologists as viewing all traits as necessarily adaptive, as they are accused of doing by the likes of Gould, Symons also argued that the female orgasm and menopause are non-adaptive, but rather by-products of other adaptations.
 This is not necessarily to say that rampant, indiscriminate promiscuity is a male utopia, or the ideal of any man, be he homosexual or heterosexual. On the contrary, the ideal mating system for any individual male is harem polygyny in which the chastity of his own partners is rigorously policed (see Despotism and Differential Reproduction: which I have reviewed here and here). However, given an equal sex ratio, this would condemn other males to celibacy. Similarly, Symons reports that “Homosexual men, like most people, usually want to have intimate relationships”. However, he observes:
“Such relationships are difficult to maintain, largely owing to the male desire for sexual variety; the unprecedented opportunity to satisfy this desire in a world of men, and the male tendency towards sexual jealousy” (p297).
It does indeed seem to be true that homosexual relationships, especially those of gay males, are, on average, of shorter duration than are heterosexual relationships. However, Symons’ claim regarding “the male tendency towards sexual jealousy” is questionable. Actually, subsequent research in evolutionary psychology has suggested that men are no more prone to jealousy than women, but rather that it is sorts of behaviours which most intensely provoke such jealousy that differentiate the sexes (Buss 1992). However, many gay men practice open relationships, which seems to suggest a lack of jealousy – or perhaps this simply reflects a recognition of the difficulty of maintaining relationships given, as Symons puts it, “the male desire for sexual variety [and] the unprecedented opportunity to satisfy this desire in a world of men”.
 Indeed, far from men being led to objectify women due to the portrayal of women in a sexualized manner in the media, Symons suggests:
“There may be no positive feedback at all; on the contrary, constant exposure to pictures of nude and nearly nude female bodies may to some extent habituate men to these stimuli” (p304).
 Admittedly, some aspects of body-type typically preferred by gay males (especially the twink) do reflect apparently female traits, especially a relative lack of body-hair. However, lack of body-hair is also obviously indicative of youth. Moreover, a relative lack of body-hair also seems to be a trait favoured in men by heterosexual women. For a discussion of the relative preference on the part of (heterosexual) females for masculine versus feminine traits in male sex partners, see the final section of this review.
 Incidentally, Symons also rejects the theory that the female menopause is adaptive, a theory which has subsequently become known as the grandmother hypothesis (p13). Also, although it does not directly address the issue, Symons’ discussion of human rape (p276-85), has also been interpreted as implicitly favouring the theory that rape is a by-product of the greater male desire for commitment free promiscuous sex, rather than the product of a specific rape adaptation in males (see Palmer 1991; and A Natural History of Rape: reviewed here).
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