My second goal is to stick to the low-hanging fruit. Almost all of the findings I report are ones that have broad acceptance within their disciplines. When a finding is still tentative, I label it as such. I know this won’t deter critics from saying it’s all pseudoscience, but I hope the experts will be yawning with boredom because they know all this already. Having done my best to accomplish those two things, I will hope for the best.
WHY THERE IS SO LITTLE ABOUT EVOLUTIONARY PSYCHOLOGY IN HUMAN DIVERSITY
Hundreds of millions of years of evolution did more than shape human physiology. It shaped the human brain as well. A comparatively new discipline, evolutionary psychology, seeks to understand the links between evolutionary pressures and the way humans have turned out. Accordingly, evolutionary psychology is at the heart of explanations for the differences that distinguish men from women and human populations from each other. Ordinarily, it would be a central part of my narrative. But the orthodoxy has been depressingly successful in demonizing evolutionary psychology as just-so stories. I decided that incorporating its insights would make it too easy for critics to attack the explanation and ignore the empirical reality.
I discuss some evolutionary material in my accounts of the peopling of the Earth and the source of greater male variance. That’s it, however, ignoring the rest of the fascinating story. The note gives you some sources for learning more.[7]
The 10 Propositions
The propositions that accompany most of the chapters are intended to exemplify low-hanging fruit. I take on an extremely broad range of topics, but with the limited purpose of clarifying a handful of bedrock issues.
I apologize for the wording of the 10 propositions—they are not as snappy as I would prefer—but there’s a reason for their caution and caveats. On certain important points, the clamor of genuine scientific dispute has abated and we don’t have to argue about them anymore. But to meet that claim requires me to state the propositions precisely. I am prepared to defend all of them as “things we don’t have to argue about anymore”—but exactly as I worded them, not as others may paraphrase them.
Here they are:
1. Sex differences in personality are consistent worldwide and tend to widen in more gender-egalitarian cultures.
2. On average, females worldwide have advantages in verbal ability and social cognition while males have advantages in visuospatial abilities and the extremes of mathematical ability.
3. On average, women worldwide are more attracted to vocations centered on people and men to vocations centered on things.
4. Many sex differences in the brain are coordinate with sex differences in personality, abilities, and social behavior.
5. Human populations are genetically distinctive in ways that correspond to self-identified race and ethnicity.
6. Evolutionary selection pressure since humans left Africa has been extensive and mostly local.
7. Continental population differences in variants associated with personality, abilities, and social behavior are common.
8. The shared environment usually plays a minor role in explaining personality, abilities, and social behavior.
9. Class structure is importantly based on differences in abilities that have a substantial genetic component.
10. Outside interventions are inherently constrained in the effects they can have on personality, abilities, and social behavior.
On all 10, the empirical record is solid. The debate should move on to new findings in the many areas where great uncertainty remains. That doesn’t mean I expect the 10 propositions to be immutable. On the contrary, I have had to keep in mind that Human Diversity is appearing in the midst of a rushing stream, reporting on a rapidly changing state of knowledge. Aspects of it are sure to be out of date by the time the book appears. My goal is to have been so cautious in my wording of the propositions that any outdated aspects of them will have been elaborated or made more precise, not overturned.
How the Phrase Cognitive Repertoires Is Used Throughout the Rest of the Book
The 10 propositions repeatedly refer to “characteristics of personality, abilities, or social behavior.” As I will occasionally put it, I am talking about the ways in which human beings differ above the neck (a loose way of putting it, but serviceably accurate).
I use personality and social behavior in their ordinary meanings. Abilities is a catch-all term that includes not only intellectual abilities but interpersonal skills and the clusters of qualities that have been described as emotional intelligence and grit. A good way of thinking about the universe of abilities is through Howard Gardner’s famous theory of multiple intelligences.[8]
From now on I will usually abbreviate personality, abilities, and social behavior to cognitive repertoires. Cognitive means that it happens in the cranium or is at least mediated there. Repertoires refers to different ways of doing things that need not be ordered from “bad” at one extreme to “good” at the other. Some of them can be so ordered, but few have bad-to-good extremes. If you’re an employer, where do you want a job applicant to be on the continuum from “extremely passive” to “extremely aggressive”? It depends on whether you’re recruiting Navy SEALs or care providers at nursing homes, and in neither case is the most extreme position the ideal one. The same is true even of something generally considered to be an unalloyed good, such as high IQ. Google may be looking for the highest possible visuospatial skills among its applicants for programmers, but the qualities that often accompany stratospheric visuospatial skills would make many of them dreadful choices as SEALs or care providers.
For most of the human qualities we will be discussing, “bad” and “good” don’t capture human differences. How many kinds of lovable are there? How many kinds of funny? How many kinds of annoying? Using the word repertoires allows for these kinds of apples and oranges too. So take note: For the rest of the book, cognitive repertoires = characteristics of personality, abilities, and social behavior.
As we embark on this survey of scientific discoveries about human diversity, a personal statement is warranted. To say that groups of people differ genetically in ways that bear on cognitive repertoires (as this book does) guarantees accusations that I am misusing science in the service of bigotry and oppression. Let me therefore state explicitly that I reject claims that groups of people, be they sexes or races or classes, can be ranked from superior to inferior. I reject claims that differences among groups have any relevance to human worth or dignity. The chapters to come make that clear.
PART I
“GENDER IS A SOCIAL CONSTRUCT”
From earliest recorded human history, everywhere and in all eras, women have borne the children and have been the primary caregivers. Everywhere and in all eras, men have dominated the positions of political, economic, and cultural power.1 From those two universal characteristics have flowed a cascade of secondary and tertiary distinctions in the status of men and women, many of which have nothing to do with their actual capabilities. In today’s language, gender has indeed been partly a social construct. Many of those distinctions were ruthlessly enforced.
The legal constraints on women in the modern West through the eighteenth century were not much short of de facto slavery. Mary Astell, often regarded as the first feminist (though she had precursors), made the point in response to John Locke’s cramped endorsement of women’s equality in the Second Treatise.2 She italicized phrases borrowed from Locke’s philosophical case for freedom: “If all men are born free, how is it that all women are born slaves? As they must be if the being subjected to the unconstant, uncertain, unknown, arbitrary will of men, be the perfect condition of slavery?… And why is slavery so much condemned and strove against in one case, and so highly applauded and held so necessary and so sacred in another?”3
If Astell’s language seems extreme, consider: An English woman at the time Astell wrote and for more than a century thereafter rarely got any formal education and had no access to university education, was prohibited from
entering the professions, and lost control of any property she owned when she married. She was obliged to take the “honor and obey” marriage vow literally, with harsh penalties for falling short and only the slightest legal protections if the husband took her punishment into his own hands. Men were legally prohibited from actually killing their wives, but just about anything less than that was likely to be overlooked. When the first wave of feminism in the United States got its start at the Seneca Falls Convention of 1848, women were rebelling not against mere inequality, but against near-total legal subservience to men.
Under those conditions, first-wave feminists were too busy to say much about questions of inborn differences between men and women. An exception was Kate Austin, who compared the plight of women to those of Chinese women with bound feet: “We know that at birth the feet of the little baby girl were straight and beautiful like her brothers, but a cruel and artificial custom restrained the growth. Likewise it is just as foolish to assert that woman is mentally inferior to man, when it is plain to be seen her brain in a majority of cases receives the same treatment accorded the feet of Chinese girls.”4 As Helena Swanwick put it, “There does not seem much that can be profitably said about [the alleged inferiority of women]… until the incubus of brute force is removed.”5 Men joined in some of the strongest early statements on nature versus nurture. John Stuart Mill coauthored “The Subjection of Women” with his feminist wife, Harriet Taylor.6 George Bernard Shaw wrote, “If we have come to think that the nursery and the kitchen are the natural sphere of a woman, we have done so exactly as English children come to think that a cage is the natural sphere of a parrot—because they have never seen one anywhere else.”[7]
After the great legal battles of first-wave feminism had been won during the first two decades of the twentieth century, a new generation of feminists began to devote more attention to questions of nature versus nurture. The result was second-wave feminism, usually dated to the publication of Simone de Beauvoir’s Le Deuxième Sexe, a massive two-volume work published in 1949. Its argument sprawled across philosophy, history, sociology, economics, and psychology. The founding statement of second-wave feminism opened the second volume: “On ne naît pas femme: on le devient.” One is not born, but rather becomes, a woman.[8]
It was an assertion that required an explanation of how and why the change from birth to adulthood takes place. The intuitive explanation of “how” is that little girls are taught to be women—what is known now as socialization theory. It refers to the ways that children are exposed to influences that shape their gender identities. The pressure can come from parental interactions in infancy and toddlerhood, as girl babies are dressed differently from boy babies and female toddlers are given dolls to play with while boys are given trucks. The pressure may take the form of encouragement by parents, teachers, or playmates to engage in sex-typed play and discouragement of behaviors that go against type, as in the case of tomboy girls and effeminate boys. Parents may teach different lessons about right behavior, emphasizing the importance of being helpful and cooperative to daughters and the importance of standing up for themselves and taking the initiative to sons. Children may be encouraged to model themselves on the parent of their own sex. In these and many other ways, sometimes subtle or unconscious, children are constantly getting signals that track with the stereotypes of males and females.
This brief characterization of socialization theory skips over a number of intense scholarly debates between learning theorists and cognitive theorists, but the debaters differ about the mechanisms at work. All agree on the basic tenet that girls are taught from infancy to be girls and boys are taught from infancy to be boys.9
Is socialization theory true? It’s natural to think so, if only because almost everybody can think of something during their childhood that involved references to what girls are supposed to be and what boys are supposed to be. Those of us who have had children of both sexes know that our interactions with our daughters and our sons have been somewhat different even if we tried hard to be gender-neutral in encouraging their abilities and ambitions.
But it’s one thing to have such personal experiences and another to demonstrate empirically that these differences in treatment as children produce the sex differences in personality, abilities, and social behavior that we observe in adult women and men. Little boys and little girls are treated differently, but how differently? “Several theoretical models suggest mechanisms that are consistent with the differential treatment of boys and girls,” wrote four Dutch scholars of childhood socialization. “However, to date there is no consensus in the literature about the extent to which parents do treat their sons and daughters differently, in which areas of parenting this mostly occurs, and whether fathers and mothers differ in the extent of gender differentiation.”10 [Emphasis in the original.]
The literature about differential socialization now consists of hundreds of titles. The note gives an overview of what has been found.[11] The short answer is that while there are lots of reasons to think that little girls and little boys are treated differently, it’s surprisingly hard to prove that the differences are more than superficial.
Apart from its empirical problems, socialization theory standing alone is unsatisfying. Yes, it provides a framework for exploring the how of the construction of artificial sex differences, but it is silent on the why. Why should it be, everywhere and throughout history, that certain differences between the sexes have been so consistent? Isn’t it simpler to assume that we’re looking at innate sex differences produced by millions of years of evolution? In 1987, psychologist Alice Eagly published Sex Differences in Social Behavior: A Social-Role Interpretation, introducing a comprehensive theory of sex differences that embraces evolution, sociology, psychology, and biology, providing an answer to the why.12 She has continued to develop the theory in the decades since, often in collaboration with psychologist Wendy Wood. Reduced to its essentials, the argument goes like this:
In the beginning was evolution, which led to physical sex differences. Males were larger, faster, and had greater upper body strength than females. Only females were capable of gestation and lactation. Given such differences, certain divisions of labor were natural. In hunter-gatherer societies, men’s greater upper body strength led societies to funnel males into social roles involving physical strength—for example, hunting and protection against predators—and to funnel women into social roles involving childcare.
Over the millennia, social roles gave rise to gender roles as people associated the behaviors of males and females with their dispositions. Women are associated with childcare not just because of biology but because of a reflexive assumption that women, more than men, have innate nurturing qualities. It is not just that men’s physical attributes make them more efficient hunters than women; it is also reflexively assumed that males have innate advantages—aggressiveness, perhaps, or initiative—that make them better hunters. This conflation of social role and gender role persists after the original physical justification for some social role has disappeared. These beliefs about stable, inherent properties of men and women have solidified without a biological foundation for them.
Enter socialization. If society has come to depend on women caring for children, little girls need to be socialized into the personality traits and skills that facilitate nurturance. If society has come to depend on men being providers and leaders, little boys need to be socialized into the personality traits that facilitate acquiring resources and status.
Social role theory includes a role for biology. “Men and women selectively recruit hormones and other neurochemical processes for appropriate roles, in the context of their gender identities and others’ expectations for role performance,” Eagly and Wood write. “Testosterone is especially relevant when, due to personal identities and social expectancies, people experience social interactions as dominance contests. Oxytocin is relevant when, due to personal identities and social expectancies, people define social interac
tions as involving bonding and affiliation with close others.”13 Biology interacts with psychology in two ways. Men and women alike psychologically internalize their gender roles as “self standards” for regulating their own behavior. They also regulate their behavior according to the expectations that others in the community have of them. “Biology thus works with psychology to facilitate role performance.”14
The interdisciplinary sweep of social role theory means that it calls upon a wide variety of empirical observations about social roles across history and across cultures, evidence from psychology about internalization of norms, social psychological experiments, the nature of sex differences in personality, demographic trends, and economics, among many others. There is no equivalent to the meta-analyses of socialization studies that permits a short characterization of the state of knowledge about the validity of social role theory. But social role theory does what socialization theory does not: It provides a comprehensive explanation of why sex is a social construct.
But is sex exclusively a social construct? That the woman in a heterosexual couple does more housework than the man even when both have full-time jobs is at least largely a gender difference—the product of culture. It may have biological roots (perhaps men have evolved to be more tolerant of a messy living space than women are). But the issue is whether differential effort in doing the housework is sustained today by culture or genes. Think of it this way: How many women who can afford to hire someone to clean the house do so? A lot.
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