In a provocative book published in 1979, "The Evolution of Human Sexuality," anthropologist Donald Symons says that men and women behave sexually in different ways because of a genetic heritage evolved and transmitted through natural selection. Sam Keen, a contributing editor to Psychology Today magazine, interviewed Symons for its February issue. The following are excerpts:

Q. Your book uses evolutionary theory to defend the hoary notion that men naturally lust after variety, while women are innately monogamous.

A: It is not a "defense" but an investigation of what human sexuality is like and an effort to explain why it is that way. Tradition and common sense tell us that men and women are different because in fact they are different. I spell out the differences and show that with respect to sexuality, there is a female human nature and a male human nature. Throughout the immensely long hunting-and-gathering phase of human evolutionary history, the sexual desires and dispositions that were adaptive for one sex were a ticket to reproductive oblivion for the other. w

Q: Let's begin with the facts of life. What are the differences between men and women?

a: The differences that are probably universal, as far as the cross-cultural literature on sexuality can detect, are:

First, competition among males over females is more intense than the reverse. Among preliterate people, male competition for women is a major theme of life. Women are both the reward of a successful warrior or hunter and a sign of status. Intergroup warfare occurs over any scarce resource, and to the male psyche, women are always in short supply. Organized fighting and killing to acquire mates does not occur among women.

Second, men incline to desire more than one wife -- polygny. In the majority of human societies, the most successful men are permitted more than one wife. Women are more malleable and, in different circumstances, seem to be satisfied with monogamy, with being a cowife, or rarely, with polyandry.

Third, men tend to experience sexual jealousy regardless of the circumstances, while women are more flexible. Selection may have favored females who could assess the threat to their reproductive interests entailed in their mates' affairs with, or marriage to, other women, and who could make the necessary compromises. Polygny was sometimes adaptive for women as well as for men, and hence there was often no sexual jealousy among cowives. Evolutionary biology explains why husbands are typically more concerned about their wives' fidelity than wives are about their husband's fidelity. Since a man may never be certain of paternity, a cuckold risks investing in the offspring of, and having his wife's reproductive efforts tied up by, a reproductive competitor.

Fourth, men are much more likely than women to be sexually aroused by visual stimuli -- the sight of a nude member of the opposite sex or even of sexually explicit pictures. There is no female market for pornography.

Fifth, cosmetic qualities, such as physical beauty and youth, are much more important determinants of women's sexual attractiveness to men than vice versa. Male attractiveness depends more on skill, prowess, power and status than on appearance.

Sixth, men are much more likely than women to desire a variety of sex partners merely for the sake of novelty.

Seventh, sex is everywhere considered a service or favor that women render to men, rather than vice versa. It is primarily men who court, give gifts in exchange for sex, use prostitutes, and rape.

Q: And the similarities between men and women?

A: As far as sexual attractiveness goes, there are common criteria. Health is obviously very closely associated with reproductive value. A good complexion, cleanliness and the absence of deformity, which are indices of good health -- those characteristics are innately attractive. There is also a tendency for the person whose height and coloration approach the mean, and whose face would most resemble a composite portrait, to be perceived as most attractive.

Q: How does evolutionary theory explain differences between male and female sexual natures?

A: Let's take the example of variety-seeking. Human sexuality was molded in, and we are genetically adapted to, the natural environment of the Pleistocene age. For over 99 percent of our history, human beings lived in small nomadic groups as hunters and gatherers. Natural selection favored those tendencies that promoted reproductive success in this situation. A males' reproductive success was potentially a direct function of the number of women he copulated with. A female's reproductive success, given the hardships of the hunting-gathering life, was probably limited to one child every three or four years, whether she copulated with one man or a thousand. An autonomous desire for variety-seeking would have been dysfunctional for women. It requires that time and energy by taken away from other reproductively useful things, such as gathering food and caring for one's children. Adulterous women also ran extreme risks from jealous husbands, and from their brothers, who had alliances with their husbands.

Q: So the double standard is built into our genes. Might not natural selection favor those women who were lusty and orgasmic?

A: Obviously the desire for, and capacity for, sexual pleasure may promote a woman's reproductive success. But there is no evidence that natural selection favored females who achieved orgasm. Male orgasm is inevitable and reproductively necessary. Female orgasm is sporadic. There are peoples among whom female orgasm is unkown and others among whom women are multiorgasmic.

Q: Why did the human female get out of the rut, lose the estrus cycle, become the sexy mammal?

A: One of the favorite pastimes of people interested in evolutionary theory these days is the loss-of-estrus game. I can propose two scenarios, both of which are probably wrong, but not as wrong as those that try to root monogamy in evolution.

Scenario One: In the Pleistocene age, males did the hunting and distributed meat to nonhunters. We know that among chimpanzees the males distribute meat more often to females who are in estrus. I hypothesize that selection favored ancestral females who advertised continuously and concealed ovulation because they received more meat.

Q: A good capitalist trick. In the sex-for-meat market, the female increased her store of the scarce commodity by a factor of 10. Thirty days a month and even on Sunday, she had favors to offer.

A: Scenario Two: I assume a different set of game conditions here, to wit, that estrus was lost after marriage evolved and that marriage is basically an agreement males make among themselves about their sexual right to females. In such a circumstance no women had the power to choose her own husband, so most women were married to less-than-ideal husbands. By not advertising ovulation, women may have minimized their husband's abilities too monitor and sequester them and maximized their ability to be fertilized by better males than their husbands.

Q: The evidence would seem to demonstrate the universal existence of rules governing and restricting the free expression of sexuality. Perhaps these reflect not a conspiracy by males or females, but a genetic corporate wisdom aimed at maximizing the number of children that can be raised to full maturity by the tribe . . .

A: . . . I assume that human beings are about the kind of creatures that they seem to be, that they love some people and hate other, that they define a small group as "the people" and consider other people fair game to be killed and conquered, that they care more about their own children than about their nieces, and more about their nieces than about someone who is unrelated. The emphasis on human beings as gentle and monogamous, as the product of environment rather than inate goals or desires, is not supported by the historical record.

I object strongly to the view that individuals are components of some mystical sociocultural system, or some larger natural harmony. I agree with the Marxist idea that you look for self-interest behind the sociopolitical views people hold. But that is not all there is. We are curious, and we also have a passion for truth -- or knowledge.

Q: How can a creature motivated by the selfish gene desire truth? You quote Michael Ghiselin with approval: "We are anything but a mechanism set up to perceive truth for its own sake. Rather, we have evolved a nervous system that acts in the interest of our gonads, and one attuned to the demands of reproductive competition."

A: We are not set up to perceive truth for its own sake, but we are set up to perceive truth because it is often useful -- that is, in our interest.

Q: You referred to the "neural underpinnings" of our desires. What does the brain have to do with the evolution of human sexuality?

A: The human brain contains richly detailed and specific mechanisms. With respect to sexuality, take the mechanism governing attractiveness, for example. If in facial features it is the composite that is most attractive, there must be an innate mechanism in the human brain that averages the faces with which it comes into contact and, totally outside of consciousness, develops a template of attractiveness by which to judge other faces.

Q: Hasn't the structure of the brain been changed by recent learning and experience?

A: The human brain was designed by natural selection to promote reproductive success in a natural environment that no longer exists. However, the brain is not a tabula rasa. The individual has emotional and motivational mechanisms that recognize and look after its interests. Otherwise it would be vulnerable to random environmental influences and exploitation. Certainly there is variation in modern and Pleistocene brains, as there is between the brains of individuals and in sexual behavior. But there are common mechanisms. Just as the members of a species may exhibit a variety of behaviors but a similar anatomy, so may the variability in human sexual behavior and custom be underlaid by certain uniformities of mind. One of the implications, and testable predictions, of my view of the evolution of human sexuality is that male and female brains will be found to be different.

Q: What difference would you predict?

A: I would expect parts of the brain to be as different as male and female genitals are. A recent experiment showed that administering low levels of dopamine drastically reduces male sexuality but has no effect of female sexuality. This suggests that male and female sexuality may be underpinned by entirely different neurological mechanisms.

Q: If the differences in the sexual natures of men and women are rooted in the brain, they are not in any real sense a matter of learning, social conditioning or nurture; they are innate. Anatomy is destiny?

A: Sociobiology bypasses or does not partake of the nature/nurture controversy.

. . . I think what is useful in trying to create a Darwinian psychology -- a term I like better than sociobiology -- is a collaboration between a Darwinian point of view, which studies the ultimate or evolutionary basis of the human psyche, and a point of view that studies the proximate basis -- the study of the brain and hormones. It is my emphasis on the psyche rather than on behavior that sets my work apart from what is commonly considered sociobiology. The idea of natural selection is going to be useful and interesting in explaining the sexual patterns we see to the extent that the brain turns out to be a richly detailed and specific structure that underpins experience.

Q: If the sexual revolution continues for another 100,000 years, give or take a few, and women continue to be aggressive, seeking variety, becoming sexually competitive, and generally acting like traditional males, would the structure of the brain change?

A: Yes, if the "liberated" women achieved greater reproductive success than more traditional women. However, I'm not sure what the so-called sexual revolution proves. Some feminists claim it was a revolution by and for males. If you read "The Hite Report," you find that many of the battle-scarred female veterans of the sexual revolution feel they have been conned and used. Despite the enormous sexual diversity, almost no woman in that study wanted casual, spontaneous sex very often, although some of them believed that they ought to want it or would be happier if they wanted it. Overwhelmingly, women want sex with feeling, not sex for its own sake or with a variety of partners. If women are really acting like men, the heterosexual world would be like nothing we have ever seen. It would be like the gay world in San Francisco. It doesn't approach that. And my prediction is that it never will.

Q: You argue that it is homosexuality rather than heterosexuality that shows us most clearly the differences between the sexes.

A: Homosexuals are the acid test for hypotheses about male-female differences in sexuality. If male and female reproductive strategies are so profoundly different, it is bound to be the case that for heterosexuality to occur at all, there has to be compromise. In homosexuality, we see male and female sexualities in their pure, uncompromised forms.

Q: And what do you see?

A: Just what you would predict. There is a substantial market for pornography among male homosexuals and, for the most part, no market among lesbians. Physical attractiveness and youth are more important determinants of sexual desirability among homosexual men than among homosexual women. The kind of sexual relations that male homosexuals typically engage in -- the one-night stand -- is simply not a pattern among most women, heterosexual or homosexual. The male gay bar is a sexual marketplace. A lesbian bar is primarily a place where women go to hang out with their friends. The male baths so prevalent in large cities exist for the purpose of anonymous, spontaneous sexuality. There is no parallel lesbian institution. Lesbians form lasting, intimate, paired relationships far more frequently and more easily than male homosexuals do. The most recent study by Alan Bell and Martin Weinberg -- a 10-year study of homosexuals in the San Francisco Bay area -- found that in the male population, 28 percent had had more than 1,000 sex partners in their lives, and 75 percent had more than 100. No woman had had 1,000 partners, and only 2 percent had had as many as 100.

Q: Another conclusion you reach which is rather unpopular in the present political climate is that rape is primarily a sexual, not a political, act.

A: That might be overstating it. There has been an immense amount of rhetoric or ideology generated around the subject of rape. Susan Brownmiller's "Against Our Will" popularized the view that rape is not motivated by male sexual desire. Certainly women experience rape as degrading, disgusting and as an act of violence. Of course rape is an act of violence. The issue is the motivation of the male who rapes. It would be absurd to deny that there are never hostile motives. It is equally absurd to say that sex plays no role.

There is no innate impulse to commit rape. But men as a group tend to value no-cost copulation, and therefore rape is likely to occur under circumstances in which they feel there is no cost to them, such as in war.

Q: The language you use throughout your analysis troubles me. Language shapes perception. Marx taught us that we often smuggle into supposedly objective analysis the ideology of a class. In your analysis, the language of capitalism reigns supreme. Selfish individuals compete for scarce resources, namely women, which will determine their reproductive success. Minimal parental investment is the clue to sexual strategy. The male advantage is to tie up as many female investments as possible, that is, to corner the market in female futures. Selection operates for the individual, not the group. Males are a market for female services. It seems highly possible that you have only slightly demythologized a Calvinist theology and presented it as evolutionary theory. Your god is a capitalist, and a male chauvinist at that. e

A: Well, I am naturally inclined to think that the perception is first and that the language is used because it is the most accurate available language. It may be economic and capitalist language, but it may nevertheless be right.

Q: In the popular mind at least, evolutionary theory has frequently been used to justify the status quo. Darwin's theory was used as the basis of the Social Darwinism that supported the privilege of the elite in the name of the survival of the fittest. Your work must be used by many philandering husbands to justify the double standard, male insensitivity and what we once called adultery. What survived has been selected. What is has passed the pragmatic court of ethics and deserves to be called good. Or, as Hegel said, "The real is the ideal."

A: I have no doubt that my work will be misused in this way. In France, there is even a right-wing group that uses sociobiological writings to support racism. I try to make it very clear that there is an unbridgeable gulf between is and ought. The theories in "The Evolution of Human Sexuality" have absolutely nothing to do with right and wrong and no implications for what one ought to do.

Q: You end your book with a statement that seems to bear on this question of free will and value: "Finally, the potentials of a biological mechanism are not necessarily constrained by, and cannot necessarily be predicted from, the purposes for which that mechanism was designed by natural selection. Perhaps it is not excessively naive to hope that a creature capable of perceiving the ploughshare in the sword is also capable of freeing itself from the nightmare of the past." How do you explain this human capacity for breaking free from our biological heritage?

A: If I knew that, I guess I would be writing another book.