The Blank Slate: The Modern Denial of Human Nature

  Women experience basic emotions more intensely, except perhaps anger.33 Women have more intimate social relationships, are more concerned about them, and feel more empathy toward their friends, though not toward strangers. (The common view that women are more empathic toward everyone is both evolutionarily unlikely and untrue.) They maintain more eye contact, and smile and laugh far more often.34 Men are more likely to compete with one another for status using violence or occupational achievement, women more likely to use derogation and other forms of verbal aggression.

  Men have a higher tolerance for pain and a greater willingness to risk life and limb for status, attention, and other dubious rewards. The Darwin Awards, given annually to “the individuals who ensure the long-term survival of our species by removing themselves from the gene pool in a sublimely idiotic fashion,” almost always go to men. Recent honorees include the man who squashed himself under a Coke machine after tipping it forward to get a free can, three men who competed over who could stomp the hardest on an antitank mine, and the would-be pilot who tied weather balloons to his lawn chair, shot two miles into the air, and drifted out to sea (earning just an Honorable Mention because he was rescued by helicopter).

  Women are more attentive to their infants’ everyday cries (though both sexes respond equally to cries of extreme distress) and are more solicitous toward their children in general.35 Girls play more at parenting and trying on social roles, boys more at fighting, chasing, and manipulating objects. And men and women differ in their patterns of sexual jealousy, their mate preferences, and their incentives to philander.

  Many sex differences, of course, have nothing to do with biology. Hair styles and dress vary capriciously across centuries and cultures, and in recent decades participation in universities, professions, and sports has switched from mostly male to fifty-fifty or mostly female. For all we know, some of the current sex differences may be just as ephemeral. But gender feminists argue that all sex differences, other than the anatomical ones, come from the expectations of parents, playmates, and society. The radical scientist Anne Fausto-Sterling wrote:

  The key biological fact is that boys and girls have different genitalia, and it is this biological difference that leads adults to interact differently with different babies whom we conveniently color-code in pink or blue to make it unnecessary to go peering into their diapers for information about gender.36

  But the pink-and-blue theory is becoming less and less credible. Here are a dozen kinds of evidence that suggest that the difference between men and women is more than genitalia-deep.

  • Sex differences are not an arbitrary feature of Western culture, like the decision to drive on the left or on the right. In all human cultures, men and women are seen as having different natures. All cultures divide their labor by sex, with more responsibility for childrearing by women and more control of the public and political realms by men. (The division of labor emerged even in a culture where everyone had been committed to stamping it out, the Israeli kibbutz.) In all cultures men are more aggressive, more prone to stealing, more prone to lethal violence (including war), and more likely to woo, seduce, and trade favors for sex. And in all cultures one finds rape, as well as proscriptions against rape.37

  • Many of the psychological differences between the sexes are exactly what an evolutionary biologist who knew only their physical differences would predict.38 Throughout the animal kingdom, when the female has to invest more calories and risk in each offspring (in the case of mammals, through pregnancy and nursing), she also invests more in nurturing the offspring after birth, since it is more costly for a female to replace a child than for a male to replace one. The difference in investment is accompanied by a greater competition among males over opportunities to mate, since mating with many partners is more likely to multiply the number of offspring of a male than the number of offspring of a female. When the average male is larger than the average female (as is true of men and women), it bespeaks an evolutionary history of greater violent competition by males over mating opportunities. Other physical traits of men, such as later puberty, greater adult strength, and shorter lives, also indicate a history of selection for high-stakes competition.

  • Many of the sex differences are found widely in other primates, indeed, throughout the mammalian class.39 The males tend to compete more aggressively and to be more polygamous; the females tend to invest more in parenting. In many mammals a greater territorial range is accompanied by an enhanced ability to navigate using the geometry of the spatial layout (as opposed to remembering individual landmarks). More often it is the male who has the greater range, and that is true of human hunter-gatherers. Men’s advantage in using mental maps and performing 3-D mental rotation may not be a coincidence.40

  • Geneticists have found that the diversity of the DNA in the mitochondria of different people (which men and women inherit from their mothers) is far greater than the diversity of the DNA in Y chromosomes (which men inherit from their fathers). This suggests that for tens of millennia men had greater variation in their reproductive success than women. Some men had many descendants and others had none (leaving us with a small number of distinct Y chromosomes), whereas a larger number of women had a more evenly distributed number of descendants (leaving us with a larger number of distinct mitochondrial genomes). These are precisely the conditions that cause sexual selection, in which males compete for opportunities to mate and females choose the best-quality males.41

  • The human body contains a mechanism that causes the brains of boys and the brains of girls to diverge during development.42 The Y chromosome triggers the growth of testes in a male fetus, which secrete androgens, the characteristically male hormones (including testosterone). Androgens have lasting effects on the brain during fetal development, in the months after birth, and during puberty, and they have transient effects at other times. Estrogens, the characteristically female sex hormones, also affect the brain throughout life. Receptors for the sex hormones are found in the hypothalamus, the hippocampus, and the amygdala in the limbic system of the brain, as well as in the cerebral cortex.

  • The brains of men differ visibly from the brains of women in several ways.43 Men have larger brains with more neurons (even correcting for body size), though women have a higher percentage of gray matter. (Since men and women are equally intelligent overall, the significance of these differences is unknown.) The interstitial nuclei in the anterior hypothalamus, and a nucleus of the stria terminalis, also in the hypothalamus, are larger in men; they have been implicated in sexual behavior and aggression. Portions of the cerebral commissures, which link the left and right hemispheres, appear to be larger in women, and their brains may function in a less lopsided manner than men’s. Learning and socialization can affect the microstructure and functioning of the human brain, of course, but probably not the size of its visible anatomical structures.

  • Variation in the level of testosterone among different men, and in the same man in different seasons or at different times of day, correlates with libido, self-confidence, and the drive for dominance.44 Violent criminals have higher levels than nonviolent criminals; trial lawyers have higher levels than those who push paper. The relations are complicated for a number of reasons. Over a broad range of values, the concentration of testosterone in the bloodstream doesn’t matter. Some traits, such as spatial abilities, peak at moderate rather than high levels. The effects of testosterone depend on the number and distribution of receptors for the molecule, not just on its concentration. And one’s psychological state can affect testosterone levels as well as the other way around. But there is a causal relation, albeit a complicated one. When women preparing for a sex-change operation are given androgens, they improve on tests of mental rotation and get worse on tests of verbal fluency. The journalist Andrew Sullivan, whose medical condition had lowered his testosterone levels, describes the effects of injecting it: “The rush of a Τ shot is not unlike the rush of going on a first date or speaking before a
n audience. I feel braced. After one injection, I almost got in a public brawl for the first time in my life. There is always a lust peak—every time it takes me unaware.”45 Though testosterone levels in men and women do not overlap, variations in level have similar kinds of effects in the two sexes. High-testosterone women smile less often and have more extramarital affairs, a stronger social presence, and even a stronger handshake.

  • Women’s cognitive strengths and weaknesses vary with the phase of their menstrual cycle.46 When estrogen levels are high, women get even better at tasks on which they typically do better than men, such as verbal fluency. When the levels are low, women get better at tasks on which men typically do better, such as mental rotation. A variety of sexual motives, including their taste in men, vary with the menstrual cycle as well.47

  • Androgens have permanent effects on the developing brain, not just transient effects on the adult brain.48 Girls with congenital adrenal hyperplasia overproduce androstenedione, the androgen hormone made famous by the baseball slugger Mark McGwire. Though their hormone levels are brought to normal soon after birth, the girls grow into tomboys, with more rough-and-tumble play, a greater interest in trucks than dolls, better spatial abilities, and, when they get older, more sexual fantasies and attractions involving other girls. Those who are treated with hormones only later in childhood show male patterns of sexuality when they become young adults, including quick arousal by pornographic images, an autonomous sex drive centered on genital stimulation, and the equivalent of wet dreams.49

  • The ultimate fantasy experiment to separate biology from socialization would be to take a baby boy, give him a sex-change operation, and have his parents raise him as a girl and other people treat him as one. If gender is socially constructed, the child should have the mind of a normal girl; if it depends on prenatal hormones, the child should feel like a boy trapped in a girl’s body. Remarkably, the experiment has been done in real life—not out of scientific curiosity, of course, but as a result of disease and accidents. One study looked at twenty-five boys who were born without a penis (a birth defect known as cloacal exstrophy) and who were then castrated and raised as girls. All of them showed male patterns of rough-and-tumble play and had typically male attitudes and interests. More than half of them spontaneously declared they were boys, one when he was just five years old.50

  • In a famous case study, an eight-month-old boy lost his penis in a botched circumcision (not by a mohel, I was relieved to learn, but by a bungling doctor). His parents consulted the famous sex researcher John Money, who had maintained that “Nature is a political strategy of those committed to maintaining the status quo of sex differences.” He advised them to let the doctors castrate the baby and build him an artificial vagina, and they raised him as a girl without telling him what had happened.51 I learned about the case as an undergraduate in the 1970s, when it was offered as proof that babies are born neuter and acquire a gender from the way they are raised. A New York Times article from the era reported that Brenda (née Bruce) “has been sailing contentedly through childhood as a genuine girl.”52 The facts were suppressed until 1997, when it was revealed that from a young age Brenda felt she was a boy trapped in a girl’s body and gender role.53 She ripped off frilly dresses, rejected dolls in favor of guns, preferred to play with boys, and even insisted on urinating standing up. At fourteen she was so miserable that she decided either to live her life as a male or to end it, and her father finally told her the truth. She underwent a new set of operations, assumed a male identity, and today is happily married to a woman.

  • Children with Turner’s syndrome are genetically neuter. They have a single X chromosome, inherited from either their mother or their father, instead of the usual two X chromosomes of a girl (one from her mother, the other from her father) or the X and Y of a boy (the X from his mother, the Y from his father). Since a female body plan is the default among mammals, they look and act like girls. Geneticists have discovered that parents’ bodies can molecularly imprint genes on the X chromosome so they become more or less active in the developing bodies and brains of their children. A Turner’s syndrome girl who gets her X chromosome from her father may have genes that are evolutionarily optimized for girls (since a paternal X always ends up in a daughter). A Turner’s girl who gets her X from her mother may have genes that are evolutionarily optimized for boys (since a maternal X, though it can end up in either sex, will act unopposed only in a son, who has no counterpart to the X genes on his puny Y chromosome). And in fact Turner’s girls do differ psychologically depending on which parent gave them their X. The ones with an X from their father (which is destined for a girl) were better at interpreting body language, reading emotions, recognizing faces, handling words, and getting along with other people compared to the ones with an X from their mother (which is fully active only in a boy).54

  • Contrary to popular belief, parents in contemporary America do not treat their sons and daughters very differently.55 A recent assessment of 172 studies involving 28,000 children found that boys and girls are given similar amounts of encouragement, warmth, nurturance, restrictiveness, discipline, and clarity of communication. The only substantial difference was that about two-thirds of the boys were discouraged from playing with dolls, especially by their fathers, out of a fear that they would become gay. (Boys who prefer girls’ toys often do turn out gay, but forbidding them the toys does not change the outcome.) Nor do differences between boys and girls depend on their observing masculine behavior in their fathers and feminine behavior in their mothers. When Hunter has two mommies, he acts just as much like a boy as if he had a mommy and a daddy.

  Things are not looking good for the theory that boys and girls are born identical except for their genitalia, with all other differences coming from the way society treats them. If that were true, it would be an amazing coincidence that in every society the coin flip that assigns each sex to one set of roles would land the same way (or that one fateful flip at the dawn of the species should have been maintained without interruption across all the upheavals of the past hundred thousand years). It would be just as amazing that, time and again, society’s arbitrary assignments matched the predictions that a Martian biologist would make for our species based on our anatomy and the distribution of our genes. It would seem odd that the hormones that make us male and female in the first place also modulate the characteristically male and female mental traits, both decisively in early brain development and in smaller degrees throughout our lives. It would be all the more odd that a second genetic mechanism differentiating the sexes (genomic imprinting) also installs characteristic male and female talents. Finally, two key predictions of the social construction theory—that boys treated as girls will grow up with girls’ minds, and that differences between boys and girls can be traced to differences in how their parents treat them—have gone down in flames.

  Of course, just because many sex differences are rooted in biology does not mean that one sex is superior, that the differences will emerge for all people in all circumstances, that discrimination against a person based on sex is justified, or that people should be coerced into doing things typical of their sex. But neither are the differences without consequences.

  BY NOW MANY people are happy to say what was unsayable in polite company a few years ago: that males and females do not have interchangeable minds. Even the comic pages have commented on the shift in the debate, as we see in this dialogue between the free-associating, junkfood-loving Zippy and the cartoonist’s alter ego Griffy:

  © Bill Griffith. Reprinted with special permission of King Features Syndicate.

  But among many professional women the existence of sex differences is still a source of discomfort. As one colleague said to me, “Look, I know that males and females are not identical. I see it in my kids, I see it in myself, I know about the research. I can’t explain it, but when I read claims about sex differences, steam comes out of my ears.” The most likely cause of her disquiet is capture
d in a recent editorial by Betty Friedan, the cofounder of the National Organization for Women and the author of the 1963 book The Feminine Mystique:

  Though the women’s movement has begun to achieve equality for women on many economic and political measures, the victory remains incomplete. To take two of the simplest and most obvious indicators: women still earn no more than 72 cents for every dollar that men earn, and we are nowhere near equality in numbers at the very top of decision making in business, government, or the professions.56

  Like Friedan, many people believe that the gender gap in wages and a “glass ceiling” that keeps women from rising to the uppermost levels of power are the two main injustices facing women in the West today. In his 1999 State of the Union address, Bill Clinton said, “We can be proud of this progress, but 75 cents on the dollar is still only three-quarters of the way there, and Americans can’t be satisfied until we’re all the way there.” The gender gap and the glass ceiling have inspired lawsuits against companies that have too few women in the top positions, pressure on the government to regulate all salaries so men and women are paid according to the “comparable worth” of their jobs, and aggressive measures to change girls’ attitudes to the professions, such as the annual Take Our Daughters to Work Day.

  Scientists and engineers face the issue in the form of the “leaky pipeline.” Though women make up almost 60 percent of university students and about half of the students majoring in many fields of science, the proportion advancing to the next career stage diminishes as they go from being undergraduates to graduate students to postdoctoral fellows to junior professors to tenured professors. Women make up less than 20 percent of the workforce in science, engineering, and technology development, and only 9 percent of the workforce in engineering.57 Readers of the flagship journals Science and Nature have seen two decades of headlines such as “Diversity: Easier Said Than Done” and “Efforts to Boost Diversity Face Persistent Problems.”58 A typical story, commenting on the many national commissions set up to investigate the problem, said, “These activities are meant to continue chipping away at a problem that, experts say, begins with negative messages in elementary school, continues through undergraduate and graduate programs that erect barriers—financial, academic, and cultural—to all but the best candidates, and persists into the workplace.”59 A meeting in 2001 of the presidents of nine elite American universities called for “significant changes,” such as setting aside grants and fellowships for women faculty, giving them the best parking spaces on campus, and ensuring that the percentage of women faculty equals the percentage of women students.60