Recent Advances in the Study of Human Differences, Part 1 of 3: Gender Differences

Human Diversity:
The Biology of Gender, Race, and Class
by Charles Murray
New York: Grand Central Publishing, 2020

“We are in the midst of a uniquely exciting period of discoveries in genetics and neuroscience (6),” notes Charles Murray near the beginning of his latest book Human Diversity, yet it remains something of a secret. Knowledgeable specialists avoid publicizing the discoveries, frequently claiming to be afraid the information will be misinterpreted and misused (i.e., by “white supremacists” and such). What they are really afraid of is retaliation by an aggressive minority of their colleagues who enforce a scientifically unsupported orthodoxy that Murray sums up in three assertions:

1) Gender is a social construct. Physiological sex differences associated with childbearing have been used to create artificial gender roles that are unjustified by inborn characteristics of personality, abilities, or social behavior.

2) Race is a social construct. The concept of race has arisen from cosmetic differences in appearance that are not accompanied by inborn differences in personality, abilities, or social behavior

3) Class is a function of privilege. People have historically been sorted into classes by political, economic, and cultural institutions that privilege heterosexual white males and oppress everyone else, with genes and human nature playing a trivial role if any. People can be resorted in a socially just way by changing these institutions. (3)

This orthodoxy has been on the defensive for many years now, and Murray is optimistic it will collapse within the coming decade. Plenty of individual believers will remain, but collectively they will lose their ability to enforce their beliefs through intimidation.

Human Diversity is a report on the revolution in our understanding of race, sex and class differences over the last thirty years. The author draws on genetic advances made possible by the sequencing of the human genome and also on neuroscience, but avoids extensive appeals to evolutionary psychology: “I decided that incorporating its insights would make it too easy for critics to attack the explanation and ignore the empirical reality.” (7)

This is part of a strategy “to stick to the low-hanging fruit” of findings “that have broad acceptance within their disciplines,” even if it leaves expert readers “yawning with boredom.” (6) Though soft-spoken by nature, Murray clearly hopes to strike an unanswerable blow against the Lysenkoist mafia whose power he has experienced personally. He conveniently summarizes his basic message in ten propositions for which “the clamor of genuine scientific dispute has abated,” (7) and there is little room left for empirically informed dispute. The first four propositions deal with sex differences, the next three with race, and the last three with class. Each proposition is given a chapter of its own.

The first proposition states that sex differences in personality are consistent worldwide and tend to widen in more gender-egalitarian cultures. Few will be surprised to find the latest studies confirming that women tend toward the warm, sympathetic, accommodating, altruistic and sociable end of the personality scale, with men more inclined to be reserved, utilitarian, unsentimental, dispassionate and solitary. Such differences emerge early in life are found around the world in radically different cultural environments.

A more counterintuitive finding is that such sex differences in personality widen rather than diminish in more egalitarian countries: this was the consistent result of five extensive international studies published between 2001 and 2018. As Murray notes, social constructivists are not the only ones surprised by this: “I know of no ideological perspective that would have predicted greater sex differences in personality in Scandinavia than in Africa or Asia.” He offers the conjecture that stronger enforcement of social norms in more traditional societies may suppress the expression of inborn personality traits, while in the modern West the sexes are “freer to do what comes naturally.” (43)

The second proposition states that “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.” Social cognition refers to the ability to infer mental states from external clues and predict other people’s intentions and reactions. Women’s superior verbal skills are a consistent finding of international student assessment tests. Women also have better sensory perception and fine motor skills, and are better than men at remembering the minutiae (peripheral detail) of events.

Men are better at remembering the gist, and have markedly superior visuospatial skills. There has also long existed a widespread perception that men are better at math than women. Recent evidence makes some qualification necessary. Within the normal ability range, the male advantage is not statistically significant. It is clearer at the high end, but even here diminished greatly during the 1980s. Among the top one percent of one percent of human mathematical ability, there were 13 boys for every girl in the 1970s; by the early 1990s, the ratio had sunk to 3 to 1, where it has remained stable ever since.

Even where men and women solve problems equally well, they may do so in different ways. For example, women tend to navigate by identifying and remembering landmarks, while men are more likely to construct mental maps. Women more often use verbal forms of logic to solve math problems, whereas men tend to use symbolic or spatial reasoning.

Among the most cherished of feminist beliefs is that female under-representation in STEM fields (science, technology, engineering and math) reflects differences in socialization—differences that would disappear in a gender-neutral society. To test this hypothesis, Murray examines the preferences and choices of a cohort chosen for a Johns Hopkins Study of Mathematically Precocious Youth (SMPY). Focusing on such a sample allows him to ignore sex differences in abilities: all these people were qualified to pursue any undergraduate major they liked.

In the upper-middle-class schools and neighborhoods where most of the SMPY girls grew up, courses were filled with inspirational stories about women scientists, political leaders, artists, and authors. High schools were putting boys and girls in the same gym classes, and high school counselors were urging female students to go into male-dominated careers. When they reached college age in 1982–5, they all knew that the most famous universities in the nation were eager to add them to their student bodies and even more eager for them to populate their majors in science, technology, engineering, and math. On campuses, young women were hearing faculty and their fellow students urging them to forgo marriage and childbearing in favor of a career. (72)

It would not be easy to find a hypothesis which has been given a fairer or larger-scale trial than the explanation of female underrepresentation in STEM fields by sex-specific socialization.

The SMPY women were, indeed, about twice as likely as women in the general population to major in STEM subjects—but so were the men compared to men in the general population, so that the sex ratio was about the same. Twice as many of the women got degrees in the social sciences, business, and the humanities as did the men. Those of the women who did major in STEM subjects inclined more to the life sciences rather than math or the physical sciences.

An important reason for the persistent underrepresentation of women in STEM fields even among the mathematically gifted elite may be that many of these women also enjoyed their sex’s natural advantage in verbal intelligence, giving them “an attractive array of alternatives to STEM” (78)—whereas the men’s intelligence was more likely to skew heavily toward mathematics.

In 2012–13 a team of Vanderbilt psychologists interviewed these SMPY men and women, by then in their late forties, about their work preferences. The women indicated a much greater willingness to consider part-time careers and a greater unwillingness to work more than forty hours a week. They sought flexibility in their work schedule and placed a high value on such things as “having strong friendships.” Murray notes that since these women were in their late forties, their preference for shorter hours and a flexible schedule was not likely to be due to the presence of small children at home.

The men expressed a strong preference for a full-time career with a high salary, and agreed with such statements as “The prospect of receiving criticism from others does not inhibit me from expressing my thoughts’ and “I believe society should invest in my ideas because they are more important than those of other people in my discipline.” They viewed “being able to take risks on my job” as a positive good, and reported that they enjoyed working with computers, tools and machines.

In short, the stated preferences of these highly talented men and women who had come of age at the height of the feminist educational and career revolution were utterly sex-typical. Yet their widely differing preferences “were not accompanied by corresponding sex differences in how they viewed their career accomplishments and close relationships, or in their positive outlook on life,” according to the Vanderbilt researchers. (76) Forcing statistically equal life outcomes on the women in this sample might have been possible under totalitarian conditions, but would almost certainly have left them less happy.

The patterns observed in this cohort of unusually talented men and women holds for people general. Consider, for example, the RIASEC psychological assessment battery widely used for career guidance: of the six dimensions of preferences and abilities it measures, two reveal large and consistent sex differences. Those who score highest on the trait labelled “Realistic” enjoy working with tools, instruments, and mechanical or electrical equipment, as well as activities such as building, repairing machinery, and raising crops or animals. Men are higher on this measure by 84 percent of a standard deviation, indicating a robust average difference. Those who score highest on the trait labeled “Social” enjoy helping, enlightening or serving others through activities such as teaching, counseling, working in service-oriented organizations and engaging in social and political studies. Women are higher on this measure by 68 percent of a standard deviation, also quite robust. And these differences do not just show up in career assessment tests, but are closely mirrored by the actual jobs men and women go on to hold.

All of this evidence goes to confirm an observation made in 1911 by Edward Thorndike, a founder of the discipline of educational psychology, that the greatest cognitive difference between men and women lies “in the relative strength of their interest in things and their mechanisms (stronger in men) and the interest in persons and their feelings (stronger in women).” (19–20) This provided the inspiration for Murray’s third proposition: “on average, women worldwide are more attracted to vocations centered on people and men to vocations centered on things.” He notes that in the late 1980s, observers could have been forgiven for predicting that the career preferences of men and women

would converge within a few decades. From 1970 through the mid-1980s, the percentage of women in Things jobs had risen and the male-female ratio had plunged. If those [trends] had been sustained, the percentages of men and women in Things jobs would have intersected around 2001. But convergence was already slowing by the late 1980s and had effectively stalled by 1990. (87)

For example, between 1971 and 1986, the percentage of women’s bachelor of science degrees in the most things-oriented STEM fields—physics, chemistry, earth sciences, computer sciences, mathematics and engineering—more than doubled, but from a base of only 4 percent to a high of 10 percent. By 1992 it had declined again to 6 percent, where it has remained ever since, give or take a percentage point. The author concludes:

It looks as if women were indeed artificially constrained from moving into a variety of Things occupations as of 1970, that those constraints were largely removed, and that equilibrium was reached around 30 years ago. (88)

The fourth proposition states that “many sex differences in the brain are coordinate with sex differences in personality, abilities and behavior.” As neurobiological researcher Larry Cahill wrote in 2017: “The past 15 to 20 years witnesses an explosion of research documenting sex influences at all levels of brain function. So overpowering is the wave of research that the standard ways of dismissing sex influences have all been swept away.” Some of the most obvious sex differences in temperament are due to sex hormones, of which testosterone and estrogen are the best known (there are many others). Both men and women produce both of these hormones, but men produce much more testosterone and women much more estrogen.

Studies have demonstrated that a single dose of testosterone administered to women

significantly altered connectivity of the network in the brain that underlies the integration and selection of sensory information during empathic behavior. This finding suggests a neural mechanism by which testosterone can impair the recognition of emotions. (100)

The administration of testosterone has also been found to diminish women’s accuracy in inferring mental states, and women with higher natural levels of testosterone have been observed to be less risk-averse than other women. Supplemental testosterone administered to men diminishes their performance on the Cognitive Reflection Test, which measures capacity to override intuitive judgments with deliberated answers. Estrogen administered to men increases their emotional response to watching a distressed person.

Among the most important but less widely known functions of testosterone is to masculinize the fetal brain. Testosterone surges in human males occur twice before birth, during weeks 12-18 and again during weeks 34-41; a third occurs in the first three months after birth. In the absence of these testosterone surges, the brain develops according to the female pattern, which is thus in some sense the “default” type of human brain.

Since this discovery was made in 1959, many experiments have been conducted on nonhuman mammals in which hormones are manipulated during critical periods of prenatal and neonatal development. It has been established that certain regions of the brain have receptors which accept chemical signals from hormones. These signals affect a cell’s anatomical connectivity and neurochemicals, and even whether it survives or not.

Complete androgen insensitivity syndrome (CAIS) is a rare but instructive disorder that affects genetically male humans, i.e., persons with a Y chromosome. Such persons produce normal amounts of testosterone at the proper time—but to no effect, because their androgen receptors do not work. Persons with CAIS are born with externally normal female genitalia, are reared as girls, and are in most respects indistinguishable from girls behaviorally.

A 2017 Swedish study identified many specific ways in which fetuses with a Y chromosome but affected by CAIS develop brains that are a mix of characteristically “male” and “female” patterns. To give just one example: they are characteristically female with regard to hippocampus volume and male with regard to caudate volume. The study concluded that similarities in brain structure between the CAIS women and female controls are due to the CAIS condition, while similarities with male controls were due to the effects of their Y chromosome.

A few defenders of feminist orthodoxy have written books critical of hormone research, and been rewarded with “uniformly and sometimes gushingly enthusiastic… reviews in the mainstream press,” according to Murray. (106) But the best that can be said for their critiques is that they have succeeded in pointing out how some research has fallen short of perfection due to “small samples, inconsistent results, and scarce replications.” (105) But neuroscientists have not put much effort into refuting these books, apart from a few of them “having had scathing things to say in blogs.” One researcher told Murray that “one reason you don’t find many critiques… is that people in the field really don’t care. It’s so evidently nonsense.” (106) In short, empirically oriented scientists live in a largely separate mental world from the armchair theorists of social constructivism.

Among the best attested neurological sex differences is the greater “laterality” of the male brain, meaning that it is “structurally optimized for communicating within hemispheres” (112) as a result of fetal masculinization. The female brain is optimized for communication across hemispheres: the corpus callosum, which connects the two hemispheres is thicker in women, even after controlling for brain size and age. Men primarily use their right hemisphere for spatial tasks and their left hemisphere for verbal tasks, while women use both hemispheres for both.

When women suffer brain damage to the left hemisphere, they are less likely than men to develop language difficulties. Women’s language test scores after brain damage suffer the same effect whether the damage occurred to the left or right hemisphere, whereas men are more affected by damage to the left hemisphere. (110)

A recent study found that males have greater connectivity between the motor and sensory systems, and in systems associated with complex reasoning and control. Females have higher connectivity with the subcortical regions associated with emotion processing. Researchers say these results “suggest a better perception-action coordination in males, and better anticipation and subsequent processing of socially and emotionally relevant cues in females.” (115)

Go to Part 2.