II

The technical literature documenting sex differences and their biological basis grew surreptitiously during feminism’s heyday in the 1970’s and 1980’s. By the 1990’s, it had become so extensive that the bibliography in David Geary’s pioneering Male, Female (1998) ran to 53 pages.2 Currently, the best short account of the state of knowledge is Steven Pinker’s chapter on gender in The Blank Slate (2002).3

Rather than present a telegraphic list of all the differences that I think have been established, I will focus on the narrower question at the heart of the Summers controversy: as groups, do men and women differ innately in characteristics that produce achievement at the highest levels of accomplishment? I will limit my comments to the arts and sciences.

Since we live in an age when students are likely to hear more about Marie Curie than about Albert Einstein, it is worth beginning with a statement of historical fact: women have played a proportionally tiny part in the history of the arts and sciences.4 Even in the 20th century, women got only 2 percent of the Nobel Prizes in the sciences—a proportion constant for both halves of the century—and 10 percent of the prizes in literature. The Fields Medal, the most prestigious award in mathematics, has been given to 44 people since it originated in 1936. All have been men.

The historical reality of male dominance of the greatest achievements in science and the arts is not open to argument. The question is whether the social and legal exclusion of women is a sufficient explanation for this situation, or whether sex-specific characteristics are also at work.

Mathematics offers an entry point for thinking about the answer. Through high school, girls earn better grades in math than boys, but the boys usually do better on standardized tests.5 The difference in means is modest, but the male advantage increases as the focus shifts from means to extremes. In a large sample of mathematically gifted youths, for example, seven times as many males as females scored in the top percentile of the SAT mathematics test.6 We do not have good test data on the male-female ratio at the top one-hundredth or top one-thousandth of a percentile, where first-rate mathematicians are most likely to be found, but collateral evidence suggests that the male advantage there continues to increase, perhaps exponentially.7

Evolutionary biologists have some theories that feed into an explanation for the disparity. In primitive societies, men did the hunting, which often took them far from home. Males with the ability to recognize landscapes from different orientations and thereby find their way back had a survival advantage. Men who could process trajectories in three dimensions—the trajectory, say, of a spear thrown at an edible mammal—also had a survival advantage.8 Women did the gathering. Those who could distinguish among complex arrays of vegetation, remembering which were the poisonous plants and which the nourishing ones, also had a survival advantage. Thus the logic for explaining why men should have developed elevated three-dimensional visuospatial skills and women an elevated ability to remember objects and their relative locations—differences that show up in specialized tests today.9

Perhaps this is a just-so story.10 Why not instead attribute the results of these tests to socialization? Enter the neuroscientists. It has been known for years that, even after adjusting for body size, men have larger brains than women. Yet most psychometricians conclude that men and women have the same mean IQ (although debate on this issue is growing).11 One hypothesis for explaining this paradox is that three-dimensional processing absorbs the extra male capacity. In the last few years, magnetic-resonance imaging has refined the evidence for this hypothesis, revealing that parts of the brain’s parietal cortex associated with space perception are proportionally bigger in men than in women.12

What does space perception have to do with scores on math tests?13 Enter the psychometricians, who demonstrate that when visuospatial ability is taken into account, the sex difference in SAT math scores shrinks substantially.14

Why should the difference be so much greater at the extremes than at the mean? Part of the answer is that men consistently exhibit higher variance than women on all sorts of characteristics, including visuospatial abilities, meaning that there are proportionally more men than women at both ends of the bell curve.15 Another part of the answer is that someone with a high verbal IQ can easily master the basic algebra, geometry, and calculus that make up most of the items in an ordinary math test. Elevated visuospatial skills are most useful for the most difficult items.16 If males have an advantage in answering those comparatively few really hard items, the increasing disparity at the extremes becomes explicable.

Seen from one perspective, this pattern demonstrates what should be obvious: there is nothing inherent in being a woman that precludes high math ability. But there remains a distributional difference in male and female characteristics that leads to a larger number of men with high visuospatial skills. The difference has an evolutionary rationale, a physiological basis, and a direct correlation with math scores.



Now put all this alongside the historical data on accomplishment in the arts and sciences. In test scores, the male advantage is most pronounced in the most abstract items. Historically, too, it is most pronounced in the most abstract domains of accomplishment.17

In the humanities, the most abstract field is philosophy—and no woman has been a significant original thinker in any of the world’s great philosophical traditions. In the sciences, the most abstract field is mathematics, where the number of great women mathematicians is approximately two (Emmy Noether definitely, Sonya Kovalevskaya maybe). In the other hard sciences, the contributions of great women scientists have usually been empirical rather than theoretical, with leading cases in point being Henrietta Leavitt, Dorothy Hodgkin, Lise Meitner, Irène Joliot-Curie, and Marie Curie herself.

In the arts, literature is the least abstract and by far the most rooted in human interaction; visual art incorporates a greater admixture of the abstract; musical composition is the most abstract of all the arts, using neither words nor images. The role of women has varied accordingly. Women have been represented among great writers virtually from the beginning of literature, in East Asia and South Asia as well as in the West. Women have produced a smaller number of important visual artists, and none that is clearly in the first rank. No female composer is even close to the first rank. Social restrictions undoubtedly damped down women’s contributions in all of the arts, but the pattern of accomplishment that did break through is strikingly consistent with what we know about the respective strengths of male and female cognitive repertoires.

Women have their own cognitive advantages over men, many of them involving verbal fluency and interpersonal skills. If this were a comprehensive survey, detailing those advantages would take up as much space as I have devoted to a particular male advantage. But, sticking with my restricted topic, I will move to another aspect of male-female differences that bears on accomplishment at the highest levels of the arts and sciences: motherhood.



Regarding women, men, and babies, the technical literature is as unambiguous as everyday experience would lead one to suppose. As a rule, the experience of parenthood is more profoundly life-altering for women than for men. Nor is there anything unique about humans in this regard. Mammalian reproduction generally involves much higher levels of maternal than paternal investment in the raising of children.18 Among humans, extensive empirical study has demonstrated that women are more attracted to children than are men, respond to them more intensely on an emotional level, and get more and different kinds of satisfactions from nurturing them. Many of these behavioral differences have been linked with biochemical differences between men and women.19

Thus, for reasons embedded in the biochemistry and neurophysiology of being female, many women with the cognitive skills for achievement at the highest level also have something else they want to do in life: have a baby. In the arts and sciences, forty is the mean age at which peak accomplishment occurs, preceded by years of intense effort mastering the discipline in question.20 These are precisely the years during which most women must bear children if they are to bear them at all.

Among women who have become mothers, the possibilities for high-level accomplishment in the arts and sciences shrink because, for innate reasons, the distractions of parenthood are greater. To put it in a way that most readers with children will recognize, a father can go to work and forget about his children for the whole day. Hardly any mother can do this, no matter how good her day-care arrangement or full-time nanny may be. My point is not that women must choose between a career and children, but that accomplishment at the extremes commonly comes from a single-minded focus that leaves no room for anything but the task at hand.21 We should not be surprised or dismayed to find that motherhood reduces the proportion of highly talented young women who are willing to make that tradeoff.

Some numbers can be put to this observation through a study of nearly 2,000 men and women who were identified as extraordinarily talented in math at age thirteen and were followed up 20 years later.22 The women in the sample came of age in the 1970’s and early 1980’s, when women were actively socialized to resist gender stereotypes. In many ways, these talented women did resist. By their early thirties, both the men and women had become exceptional achievers, receiving advanced degrees in roughly equal proportions. Only about 15 percent of the women were full-time housewives. Among the women, those who did and those who did not have children were equally satisfied with their careers.

And yet. The women with careers were four-and-a-half times more likely than men to say they preferred to work fewer than 40 hours per week. The men placed greater importance on “being successful in my line of work” and “inventing or creating something that will have an impact,” while the women found greater value in “having strong friendships,” “living close to parents and relatives,” and “having a meaningful spiritual life.” As the authors concluded, “these men and women appear to have constructed satisfying and meaningful lives that took somewhat different forms.”23 The different forms, which directly influence the likelihood that men will dominate at the extreme levels of achievement, are consistent with a constellation of differences between men and women that have biological roots.

I have omitted perhaps the most obvious reason why men and women differ at the highest levels of accomplishment: men take more risks, are more competitive, and are more aggressive than women.24 The word “testosterone” may come to mind, and appropriately. Much technical literature documents the hormonal basis of personality differences that bear on sex differences in extreme and venturesome effort, and hence in extremes of accomplishment—and that bear as well on the male propensity to produce an overwhelming proportion of the world’s crime and approximately 100 percent of its wars. But this is just one more of the ways in which science is demonstrating that men and women are really and truly different, a fact so obvious that only intellectuals could ever have thought otherwise.