Sex on the Brain

Males tend to seek more than one mate. "Monogamy is rare in mammals, almost unheard of in primates," according to zoologist David Barash, "and it appears to be a relatively recent invention of certain human cultures.... Prior to Western colonialism and Judaeo-Christian social imperialism, the vast majority of human societies were polygynous."

While many women seem to think that polygamy works to the advantage of males, in truth it works to the advantage of females in many ways. For it is the woman who is the possessor of the evolutionary treasure—potential reproduction—and she is the one who parcels out the treasure, and only to those whom she finds satisfactory. As Harvard anthropologist Irven DeVore insists, "Males are a vast breeding experiment run by females."

As possessor of the treasure, the female can require males to do whatever she wants. Among the things she requires is that the males compete with one another. Evolutionarily speaking, she is separating the strong genes from the weak. And so, when she has found the male she feels is an acceptable father for her offspring, she will join with him. That the male may have other wives does not diminish his genetic fitness. And once she is pregnant, it does not matter how he expends his sperm. Sperm is cheap, but her egg is dear.

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Everywhere and at all times, sex has been seen as a service or a favor that women choose to provide or offer to men. There are no cultures in which the opposite is the cultural norm. It is the males who hire prostitutes and engage them purely for the purposes of having sex, while the use of male prostitutes is extremely rare and usually involves not simply a woman purchasing sex but also companionship and a stable relationship. It is men who court women, give them gifts, take them to dinner (just as primitive hominid hunters millions of years ago shared their meat with the female), woo them and ask indirectly or directly for sex. It is women who resist, are coy, reserved, cautious, "modest," calculating (to ascertain the man's potential value as a loyal and protective mate) and who choose indirectly or directly to have sex.

This is true throughout the world. Margaret Mead described this sex difference in Polynesia: "It is the girl who decides whether she will or will not meet her lover under the palm trees, or receive him ... in her bed in the young people's house. He may woo and plead ... [but] if she does not choose ... she does not lift the corner of her mat, she does not wait under the palm trees."

As Donald Symons, professor of anthropology at the University of California, Santa Barbara, asserts, "Women control what males have always needed—the ability to carry and reproduce their genes for them. And so a man tends to pursue sex aggressively—it's a trivial expenditure of energy with a potentially big payoff. For a woman, though, sex is something else. Women, after all, have always had one of their few, expensive eggs and their bodies on the line. And so sex for a woman remains a valuable service, a service that has to be carefully traded."

These differences in sexual strategies between males and females spring not from sex-role training but from traits and behavior patterns that over millions of years of hunter-gatherer culture proved to have survival value, were favored by natural selection and, as a result, became hard-wired into the expanding human brain.

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Today, survival of the fittest no longer requires hunting or gathering traits. However, our culture has been moving away from the hunter-gatherer phase for only some 10,000 years and, as anthropologists agree, physical evolution is extremely slow, and there is no evidence or reason to believe that contemporary human bodies or brains differ from those of 10,000 years ago. In fact, recent evidence indicates that humans anatomically identical to modern humans were hunting the fields of the Middle East more than 90,000 years ago.

So despite the fact that we live in a culture with little resemblance to the hunter-gatherer culture in which we evolved, there's no doubt that we are genetically adapted to that environment.

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Calvin Coolidge is not one of our nation's most celebrated Presidents, but Silent Cal secured himself a place in the indexes of evolutionary biologists and students of sexual behavior when he and his wife were being conducted on separate tours of a Government farm. Mrs. Coolidge stopped to observe the chicken coops and asked her guide how often the rooster there would perform his sexual duties each day. "Oh, dozens of times," said her guide. Mrs. Coolidge raised her eyebrows, clearly impressed. "Please tell that to the President," she requested.

When the President later came to the coops and observed the rooster's performance, he was informed of his wife's request.

"Same hen every time?" asked the taciturn President.

"Oh, no, sir," said the guide, "a different one each time."

The President nodded and said, "Please tell that to Mrs. Coolidge."

It is another of our apparently universal facts that men are far more likely than women to desire a variety of sex partners. When a male mammal is introduced into a cage with a sexually receptive female, he will copulate with verve. After a period of time, however, he will begin to lose interest, even though the female is as sexually receptive as ever. Finally, he will reach a point where he has no inclination to copulate at all. However, if the female is removed and replaced by a new female, the male will immediately begin copulating with renewed enthusiasm—a phenomenon dubbed the Coolidge Effect.

Rams, for example, will lose interest in ewes after four or five copulations. But when a new ewe is introduced, the ram will be restored to its former vigor. This will happen every time another ewe is substituted, and the ram's rate of ejaculation will be the same with the 12th ewe as it was with the first. A similar sexual dynamic exists between bulls and cows. Researchers have tried to fool the rams and bulls by disguising females with which they have mated, covering their heads and bodies with canvas sacks or masking their vaginal odors with other smells and reintroducing them, but the males are not fooled. As psychologist Glenn Wilson has observed, "These male animals know where they have been and do not like going over the same ground again."

The increased intelligence of human beings has made it more likely that mates will maintain interest in each other. There's no doubt that an intelligent, sexually creative woman can keep a man's attention, devotion and love for a lifetime. Nevertheless, to a lesser degree, the Coolidge Effect applies among humans.

Surveys show that far more males than females commit adultery. In recent years, this gap is closing, but there is evidence that increasing female infidelities are the result of a general loosening of sexual standards, rather than of a change in female attitudes. When surveys look at beliefs rather than behavior, the sex differences remain wide: Surveys that ask whether people would like to engage in extramarital sex indicate that the difference between males and females is far greater than in actual extramarital sex.

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Which brings us to our next universal and biologically influenced difference between the sexes; perhaps it is the basis of the differences mentioned above. Dr. Helen Singer Kaplan, of New York City's Cornell Medical Center, speaking from a lifetime of research and clinical experience in human sexuality, asserts, "I think all the differences between male and female sexuality are due to the strength of the male sex drive, which seems much higher than the female's. All other differences follow from that.

"The male sex drive is so compelling that it's less subject to inhibition by learning than the female's, which is more variable, flexible and influenced by experience. A woman can be aroused and have more orgasms than a man, but she isn't driven to sexuality the way a man is. The male sex drive is much more difficult to suppress. For example, if you tell a little girl not to masturbate, she's likely to listen to you, but a boy will continue to masturbate, in part because his urge is much stronger. I'm not saying there aren't crucial cultural factors present in sexuality, of course, but I believe the biological factors in our sexual behavior have been neglected."

How do we measure the intensity of something called a sex drive? Scientists have tried everything from penis meters that gauge the intensity of erections to tiny transmitters placed in the vagina to send messages about the quantity of secretions, to sampling the amount of adrenaline in the blood stream of persons watching pornography. But who's to say that X amount of vaginal secretions indicates a higher sex drive than Y degree of penile erection?

Certainly, it has been males who have throughout history been the overwhelming consumers of pornography. It is mostly males who use prostitutes and give gifts in exchange for sex. There's no doubt that a greater percentage of males than females masturbate, and do so earlier and far more frequently than females. As we have seen, males are more likely to desire more than one mate and to seek variety and novelty in sex partners. Surveys of the frequency with which males and females engage in sex indicate that males at all ages have sex more frequently.

But such facts and behaviors are imprecise and inconclusive. That is why more and more scientists are seeking to understand human nature not by reference to behavior but in the actual (continued on page 88)Sex on the Brain(continued from page 78) structure and electrochemistry of the brain.

The Brain-Mind Revolution

A "brain revolution" has been taking place in the past decade or so. Due to advances in microchip technology and other technological tools, brain scientists have at last been able to see what is going on in those billions of tiny brain cells that are linked together in a network of unsurpassed and almost infinite complexity. Neuroanatomist Floyd Bloom of Scripps Clinic in La Jolla, California, describes the new capabilities: "A neuroscientist used to be like a man in a Goodyear blimp floating over a bowl game: He could hear the crowd roar, and that was about it. But now we're down in the stands. It's not too long before we'll be able to tell why one man gets a hot dog and one man gets a beer."

Of all the new findings of the late Seventies and the Eighties, one thing could not escape the neuroscientists' attention: the noticeable differences between the brains of men and the brains of women.

What goes on in the brain and in the mind depends on the levels of neurotransmitters, neuropeptides and hormones. And the brains of men and those of women differ in the quantities of certain neurochemicals they secrete, as well as in the way they respond to doses of those neurochemicals. A neurotransmitter such as dopamine has a sexually stimulating effect on men but not on women, while serotonin seems to be sexually exciting for women only.

Males and females, it is now becoming clear, differ not only in the way the brain hemispheres are organized but also in their very structure and physiology. The right hemisphere of males, for example, is noticeably larger and heavier than the right hemisphere of females. The verbal capacity of males is largely confined to one hemisphere, while that of females appears to be spread more diffusely across both hemispheres. And scientists have been finding a variety of other anatomical differences in the brains of the sexes as well.

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Since brain anatomy influences behavior, physiologists of behavior are now finding that many of the long-noted behavioral differences between the sexes have their roots in anatomical and neurochemical brain differences. For example, scientists have recently begun investigating the mysteries of power and the way it flows through and alters societies, and are discovering that power, and the social manipulations that are used to secure and maintain it—that is, politics—are a function of biochemistry.

In fact, there is such a flood of new evidence into this fusion of neurochemistry and power that an entire new field of research has begun to take shape, a field the scientists call biopolitics. Among the extraordinary findings in this field are those demonstrating that male power and dominance are linked to high levels of the neurochemical serotonin. In studies of primates ranging from monkeys to baboons to chimps to humans, a variety of researchers have consistently found that dominant males have high levels of serotonin; that when a dominant male is removed from his position of dominance, his levels of serotonin plummet and his former unshakeable self-assurance turns into insecurity and anxiety; that when nondominant males are given chemicals to boost their serotonin levels, they begin to behave like dominant males—confident, self-assured, assertive, even aggressive.

This connection between brain chemistry and power seems inseparable from sexual chemistry: Scientists have discovered that there is a direct link between social dominance and sexual potency, between power and sex. Interestingly, this link works in both directions, in what is known as a "bidirectional feedback loop" between sex and power. Sexual access to females, research is revealing, is in many ways dependent on a certain amount of dominance (and its associated qualities of confidence and assertiveness), which means high levels of serotonin (among other things). But it has also been found that sexual activity and potency itself will raise the level of serotonin in formerly submissive or passive males, and when dominant males are removed from access to sexual activity, or denied sexual activity, their levels of serotonin (and their dominance) decline sharply. Thus, in ways that are still to be fully understood, sex and power are interdependent.

The T Factor

Testosterone is an anabolic steroid—that is, it promotes the synthesis of proteins from food and promotes the growth and regeneration of tissue (unlike the female hormone estrogen, a catabolic steroid, which promotes the breakdown of proteins and leads to the increased storage of fat on the body). Since males have far greater quantities of testosterone than females, males are generally larger than women. Their bodies are also different in their make-up: on the average, the bodies of males are about 40 percent muscle and 15 percent fat, while the bodies of females are about 23 percent muscle and 25 percent fat. Men have wider shoulders and longer arms, they deliver oxygen to their muscles more efficiently and, pound for pound, their upper body is two to three times more powerful than a woman's.

Testosterone is most highly concentrated in the hypothalamus, and scientists have recently discovered that the injection of testosterone has an excitatory influence on the hypothalamus and the limbic system, which is to say on that part of the brain regulating emotions, sex and aggression. Biological anthropologist and medical doctor Melvin Konner points out, "It is one thing to say that the hormone probably influences sex and aggression by acting on the brain; it is quite another to find a major nerve bundle deep in the brain, likely to be involved in sex and aggression, that can fire more easily when testosterone acts on it than when it does not. A key link in the story has been formed."

Perhaps the most intriguing fact about testosterone is that scientific evidence indicates that it is necessary for male sexual arousal and desire. Testosterone, recent studies have shown, is a genuine aphrodisiac. Physiologist Julian Davidson and colleagues at Stanford University performed a study of men suffering from extremely low levels of sexual desire as the result of underactive gonads. They found that doses of testosterone dramatically increased their frequency of sexual fantasies and restored their sexual desire. Said Davidson, "It's very clear that testosterone is the biological substrate of desire, at least in men."

Testosterone is so essential to male sexual desire that one method now being used to treat male sexual offenders is to require them to take drugs (such as Depo-Provera) that sharply reduce their levels of testosterone. According to medical psychologist John Money of Johns Hopkins, the reduction in testosterone "suppresses or lessens the frequency of erection and ejaculation and lessens the feeling of libido and the mental imagery of sexual arousal."

There is evidence that when males are anticipating sexual activity, their levels of testosterone increase. Another study indicates that testosterone levels in males increase both before and after sex.

But even though it is a "male" hormone, testosterone also plays an important role in female sexual desire. Although females produce testosterone in smaller quantities than do males, that (continued on page 152)Sex on the Brain(continued from page 88) small amount has powerful effects: Scientists have found that females experience substantial decreases in sexual activity if they are no longer producing testosterone. On the other hand, if testosterone is administered to females, it increases both sexual desire and frequency of sexual activity.

Gatekeepers and Seekers

Given the fact that males have higher levels of testosterone than females, it's hard to escape the conclusion that males apparently, on the average, have a stronger drive or desire to engage in sexual activity than do females. A vast number of studies, including cross-cultural studies, support this conclusion.

Much evidence indicates that for men, most women, including strangers, are perceived as potential sexual partners, while women are more likely to perceive as potential sexual partners only men whom they already know. Males tend to attribute more sexual meaning to a wide range of behaviors than do females: They expect that women who wear "sexy" clothing desire sex, and they are more likely to interpret female friendliness as sexual interest.

A recent survey of 289 sex therapists revealed that the most common complaint among couples was a discrepancy between partners in their desire for sex. In most cases, the males' desire was greater than that of the females. In a 1982 study of receptivity to heterosexual invitations by strangers, males and females were approached and told by members of the opposite sex that "I've been noticing you around campus, and I find you to be very attractive." This statement was followed by one of three invitations: Would you go out on a date with me? Would you come to my apartment? or Would you go to bed with me? Men and women were equally likely to accept the date; about 50 percent said yes. But about 70 percent of the men were willing to go to the woman's apartment, while only six percent of the women accepted that offer. And fully 75 percent of the men were quite willing to go to bed with the unknown woman, while none of the women accepted that offer. That is, males were far more eager to go to bed with a woman they had just met than they were to go out on a date with her.

Even the most recent studies show that both men and women report that it is the male who usually initiates the sexual behaviors in which the couple engage, that it is usually the male who requests increased sexual intimacy and the females are virtually always the ones to limit a couple's sexual activity. Kansas State University psychologist and sex researcher William Griffitt summarizes the findings of a number of recent studies with the observation, "Part of being masculine for males is sexual success, and part of being feminine for females is limited sexual accessibility."

So despite the sexual revolution, despite more than 25 years of feminists' pursuing sexual equality, the ancient pattern endures: Males are the seekers and females the gatekeepers of sex.

When looked at from an evolutionary viewpoint, in terms of differing reproductive strategies, this sex difference makes perfect sense. As neuroscientist Candace Pert puts it, "Of course, men and women have entirely different attitudes toward sex, and those attitudes are hardwired in the brain, not learned.... The brain doesn't know the pill was invented. Women are programed since time immemorial to get that guy back to take care of any offspring that might ensue. After all, our mothers had babies, our grandmothers had babies; women alive today are the result of a long line of women who reproduced."

What Pert describes is the innate sex difference in parental investment or optimal mating strategy: Females can produce fewer offspring than can males, must invest more of their own life in each child, and thus must be more selective in their sexual partners. So, in evolutionary terms, females with lower levels of testosterone would tend to be selected for, while those with higher levels would tend to produce fewer surviving offspring, and thus to disappear from the gene pool.

It's easy to see why this is so. Females with lower levels of testosterone would tend to have less intense sexual desire, and thus would be less likely to have sex impulsively and indiscriminately. They would be able to control their own sexual appetites more, and thus be able to choose their sexual partners more pragmatically, with an eye toward which would be the best providers and protectors of their offspring and showed evidence of possessing genes that would contribute to the successful survival of their offspring. Also, since such a female would be less likely to seek other males for sex partners, the male she did mate with would be more certain that any offspring were his, and would be more likely to invest his time and energy in care of those offspring, thus increasing their chance of survival.

Females with high levels of testosterone, on the other hand, would have less evolutionary success for several reasons. For example, since they would tend to mate more frequently and with a wider variety of males, they would be less selective in choosing their sexual partners and more likely to become pregnant by an inappropriate male—one who was genetically less desirable, less capable of caring for offspring or one who had no desire to care for any offspring.

On the other hand, powerful sexual desire has clear reproductive advantages for males: Those males capable of being aroused quickly and frequently by females will be more likely to seek out sexual partners and be more capable of taking advantage of those mating opportunities that arise than will males with little or no sexual desire. As we have seen, testosterone level is strongly related to experienced sexual desire. Testosterone is essential for male sexual arousal, and higher levels of testosterone seem to produce males who are more easily aroused and arousable, and more likely to engage in sexual activities. So, in evolutionary terms, males with relatively high levels of this biochemical would tend to be selected for.

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To reproduce, males must not only be sexually attracted to females and desire to have sex with them, they must actually succeed in having sex with them. And in this regard, as all males quickly and painfully learn, there is a yawning gap between intention and reality. From the male's point of view, there simply aren't enough females to go around, and so a male must compete for sexual success with other sexually seeking males. In many species, this involves vicious battles between males.

It makes sense, in evolutionary terms, that the same biological factors that would cause males to seek sex (sexual desire and arousal) would also provide them with the capacity to attain sex—the capacity to compete, physically if necessary, with other males for access to females. Since such competition can be dangerous, we would expect that the biological factors involved in seeking sex and in aggression would also be linked with danger and fear, or what scientists have called the "fight or flight" response. There is much evidence that testosterone is involved in that response.

Still, it's clear that too much testosterone can be as fatal for a male's genetic survival as too little. Studies linking high testosterone with violent criminals and other antisocial behavior provide evidence of how the simple capacity for aggression, the preference for dominance, can, propelled by too much testosterone, lead males into self-destructive behavior. Men who love war too much do not survive to reproduce, and males who spend their reproductive years behind bars are not winners in the reproductive sweepstakes.

Furthermore, highly or uncontrollably aggressive males are simply too dangerous for societies to have around. There is evidence that females are not sexually receptive to males who are too aggressive, since they threaten their safety and reproductive success. Often it is the other males who, for their own safety and reproductive futures, will band together to weed out those berserkers.

UCLA psychiatrist Michael McGuire has spent some 13 years studying patterns of behavior among monkeys, and points out an intriguing dynamic between violence and dominance. The dominant male monkey, he says, is not "a big bully who pushes everybody around. He's just the opposite, really. It's the subordinate males who are nasty and grumpy; when a male becomes dominant, all of a sudden he becomes benevolent, sweet. He sits with the females and grooms them.... He's less aggressive when he's dominant. The fight is to get there, but once you're established and everybody acknowledges your power, you keep the peace."

The dominant male, McGuire points out, "does what he wants" and has "access to any resources, including the females." And yet, "if you watch closely, you see that the females select [a subordinate] male that they groom with.... Within two weeks, the male favored by the females will be dominant. Now, do the females know something we don't know?"

The aggressive, "proactive" power is essential for a male's reproductive success, but it is constantly confronted with the female power to attract and select.

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In any discussion of reproductive strategies, the question is not what males or females "choose" to do but, rather, what impulses, drives and behavior patterns have evolved by natural selection because they are the types of impulses, drives and behavior patterns whose possessors' genes tend to get multiplied most. The human brain, evolved by natural selection, is built to promote the survival of the genes that created it, not to understand itself or be conscious of its own motives.

These reproductive strategies favored by evolution are not necessarily reproductive strategies favored today—some are outmoded, undesirable or socially unacceptable. We are no longer hunter-gatherers. But we have stopped being hunter-gatherers for only a few thousand years, and the reproductive strategies we may now disapprove of have been hardwired into us over hundreds of thousands or millions of years.

There is another type of evolution known as cultural evolution, which involves alterations, not encoded in genes but in information stored in minds, changes in the habits, attitudes and capabilities humans have acquired in society.

Thus, while our genetic sexuality may be concerned with finding ways to successfully propagate our own genes, cultural evolution is selecting strategies that include somehow countermanding those drives and ending the catastrophic growth of world population.

The only hope for humankind is through learning, education, increased wisdom and heightened awareness of what we are up against. Part of this essential wisdom must be a clear awareness of our own natures, our own sexual drives—however outmoded they may be—clinging to us from the days when we were chasing the woolly mammoth across the savanna.

"Scientists have discovered a link between social dominance and potency, between power and sex."

"Males were more eager to go to bed with a woman they had just met than to go on a date with her."