The gender equality 'paradox' and genetics

Is there a general factor of sexual dimorphism that differs by population?

There's a number of studies that find that egalitarian cultural values correlates with larger not smaller actual measured sex differences. These are the first major studies using large international surveys:

• Costa Jr., P. T., Terracciano, A., & McCrae, R. R. (2001). Gender differences in personality traits across cultures: Robust and surprising findings. Journal of Personality and Social Psychology, 81(2), 322–331. https://doi.org/10.1037/0022-3514.81.2.322

Secondary analyses of Revised NEO Personality inventory data from 26 cultures (N =23,031) suggest that gender differences are small relative to individual variation within genders; differences are replicated across cultures for both college-age and adult samples, and differences are broadly consistent with gender stereotypes: Women reported themselves to be higher in Neuroticism, Agreeableness, Warmth, and Openness to Feelings, whereas men were higher in Assertiveness and Openness to Ideas. Contrary to predictions from evolutionary theory, the magnitude of gender differences varied across cultures. Contrary to predictions from the social role model, gender differences were most pronounced in European and American cultures in which traditional sex roles are minimized. Possible explanations for this surprising finding are discussed, including the attribution of masculine and feminine behaviors to roles rather than traits in traditional cultures.

• Lippa, R. A. (2009). Sex Differences in Sex Drive, Sociosexuality, and Height across 53 Nations: Testing Evolutionary and Social Structural Theories. Archives of Sexual Behavior, 38(5), 631–651. https://doi.org/10.1007/s10508-007-9242-8

By analyzing cross-cultural patterns in five parameters—sex differences, male and female trait means, male and female trait standard deviations—researchers can better test evolutionary and social structural models of sex differences. Five models of biological and social structural influence are presented that illustrate this proposal. Using data from 53 nations and from over 200,000 participants surveyed in a recent BBC Internet survey, I examined cross-cultural patterns in these five parameters for two sexual traits—sex drive and sociosexuality—and for height, a physical trait with a biologically based sex difference. Sex drive, sociosexuality, and height all showed consistent sex differences across nations (mean ds = .62, .74, and 1.63). Women were consistently more variable than men in sex drive (mean female to male variance ratio = 1.64). Gender equality and economic development tended to predict, across nations, sex differences in sociosexuality, but not sex differences in sex drive or height. Parameters for sociosexuality tended to vary across nations more than parameters for sex drive and height did. The results for sociosexuality were most consistent with a hybrid model—that both biological and social structural influences contribute to sex differences, whereas the results for sex drive and height were most consistent with a biological model—that evolved biological factors are the primary cause of sex differences. The model testing proposed here encourages evolutionary and social structural theorists to make more precise and nuanced predictions about the patterning of sex differences across cultures.

• Lippa, R. A. (2010). Sex Differences in Personality Traits and Gender-Related Occupational Preferences across 53 Nations: Testing Evolutionary and Social-Environmental Theories. Archives of Sexual Behavior, 39(3), 619–636. https://doi.org/10.1007/s10508-008-9380-7

Using data from over 200,000 participants from 53 nations, I examined the cross-cultural consistency of sex differences for four traits: extraversion, agreeableness, neuroticism, and male-versus-female-typical occupational preferences. Across nations, men and women differed significantly on all four traits (mean ds = −.15, −.56, −.41, and 1.40, respectively, with negative values indicating women scoring higher). The strongest evidence for sex differences in SDs was for extraversion (women more variable) and for agreeableness (men more variable). United Nations indices of gender equality and economic development were associated with larger sex differences in agreeableness, but not with sex differences in other traits. Gender equality and economic development were negatively associated with mean national levels of neuroticism, suggesting that economic stress was associated with higher neuroticism. Regression analyses explored the power of sex, gender equality, and their interaction to predict men’s and women’s 106 national trait means for each of the four traits. Only sex predicted means for all four traits, and sex predicted trait means much more strongly than did gender equality or the interaction between sex and gender equality. These results suggest that biological factors may contribute to sex differences in personality and that culture plays a negligible to small role in moderating sex differences in personality.

These studies relate sex differences in various phenotypes, including height and various kinds of survey based traits, to country indicators of sex egalitarianism, such as UN's index. Surprisingly to feminist models, some personality differences and occupational choices and preferences are larger in the more sex egalitarian countries. That is to say, in countries with strong egalitarian values for men and women, men and women are actually more different. The usual theory offered for this pattern from conservative leaning researchers is based on choice. In more free countries, women are more free to choose occupations, behaviors, and personalities that reflect their innate tendencies. If you grow up in a place where taking care of children doesn't pay a living, but you nevertheless need a job, you might take up programming. In cultures where women can easily get a solid government job doing female things, such as being a nurse or daycare worker, they aren't very likely to take up something as boring to them as programming. The choice model works for occupations, but not for personality traits which aren't really chosen. Still, one could repair this by saying that people modify their personalities to fit their occupations, so that women who enter nursing, say, end up more agreeable and more depressed than women who took up careers as programmers or engineers. It's speculative for sure.

There are many additional findings along these lines using other datasets and phenotypes:

• Basic values using the European Social Survey

• Subjective well-being, using the PISA 2015-2018 surveys

• Ability differences on subtests in the PISA

• Teenagers preferences for job types, ROSE project

• Even meat consumption

There's some social psychologists who comically try to blame this on stereotypes causing sex differences rather than the other way around (what else?).

I want to propose a different theory, an obvious idea from an HBD perspective. What if sex differences evolved to have different sizes, and the countries that are egalitarian in values, rich, developed etc. are those with the largest such natural differences? The economic argument for this model is simple: sexual division of labor is efficient because it allows for greater specialization. Egalitarianism is a package deal, it seems, it goes together with individualism and meritocracy and even monogamy and late marriages. Kevin MacDonald speculates (in Individualism and the Western Liberal Tradition), that differences in this package have genetic roots. In contrast to those who think this package resulted from the church's ban on incestuous marriages, he quotes Roman historian Tacitus discussing meritocracy, individualism, and egalitarianism in Germanic tribes (Chapter 8):

7. In the election of kings they have regard to birth; in that of generals, to valor. Their kings have not an absolute or unlimited power; and their generals command less through the force of authority, than of example. If they are daring, adventurous, and conspicuous in action, they procure obedience from the admiration they inspire. None, however, but the priests are permitted to judge offenders, to inflict bonds or stripes; so that chastisement appears not as an act of military discipline, but as the instigation of the god whom they suppose present with warriors. They also carry with them to battle certain images and standards taken from the sacred groves. It is a principal incentive to their courage, that their squadrons and battalions are not formed by men fortuitously collected, but by the assemblage of families and clans. Their pledges also are near at hand; they have within hearing the yells of their women, and the cries of their children. These, too, are the most revered witnesses of each man's conduct, these his most liberal applauders. To their mothers and their wives they bring their wounds for relief, nor do these dread to count or to search out the gashes. The women also administer food and encouragement to those who are fighting.

8. Tradition relates, that armies beginning to give way have been rallied by the females, through the earnestness of their supplications, the interposition of their bodies, and the pictures they have drawn of impending slavery, a calamity which these people bear with more impatience for their women than themselves; so that those states who have been obliged to give among their hostages the daughters of noble families, are the most effectually bound to fidelity. They even suppose somewhat of sanctity and prescience to be inherent in the female sex; and therefore neither despise their counsels, nor disregard their responses. We have beheld, in the reign of Vespasian, Veleda, long reverenced by many as a deity. Aurima, moreover, and several others, were formerly held in equal veneration, but not with a servile flattery, nor as though they made them goddesses.

To be fair, how did Tacitus really know what the Germanics were like? He didn't, but he had some guesses based on talking to traders, reading other works and so on.

It seems difficult to test this genetic theory. One cannot just compute polygenic scores and look at the sex differences. The genes on the autosomes (chromosomes 1-22) mix up every generation, so the sex differences on these are always near-zero (it can be larger than zero in a given generation if mortality for one sex relates to the scores, say if less intelligent men die more than women, within a generation, men would have a slight polygenic score advantage for intelligence). Genetic sex differences, then, must result from the sex chromosomes (X and Y), and their interactions with the other genes. For instance, the reason that men are taller than women is not that men have a higher autosomal polygenic score for height, but rather that some of the genes controlling height growth interact with sex hormones. Imagine a gene that promotes growth, say, by making legs longer. Now imagine a mutation that causes this gene to be sensitive to estrogen as an inhibitor. The more estrogen is detected, the less the gene is expressed. This gene would now function to make men taller than women. Nothing prevents such genes from varying by population, so evolution can control the degree of sexual dimorphism. We know from comparative studies of non-human monkeys and other animals that there can be quite the variation in sexual dimorphism:

Size and mass is easy to measure, so most research focuses on this ("sexual size dimorphism"), but what about sexual dimorphism in behavior? This is more difficult. Genetic prediction models (GWASs) do not look for such interactions currently, so we currently don't have any way to directly examine this, even for height. For this reason, we cannot use our current models to examine population differences, whether current populations of ancient genomes.

One interesting finding is that the countries where men and women differ more in height (male height / female height), are also the taller countries.

This kind of pattern suggests that the evolution of stature was sex-related. That is, if male height is advantageous to fertility in a given population but not female height (or less so), this will result in an increase in the autosomal genes that make both sexes taller, but evolution will also select for genes that make just men taller. (This study speculates that this runaway selection for men height among the Dutch is why they are so tall.) As a result of this double effect of selection, the sex difference will become correlated with the population mean. In theory, then, if selection for high intelligence in humans in the last 1000s of years was mainly due to male-related selection, then the male advantage should be larger among the higher intelligence populations. In fact, the height gaps are also larger in the more developed countries:

In other words, for the kind of sexual dimorphism that we can easily measure between countries, and thus races/populations, it does appear that sexual dimorphism is larger in the more developed ones. No doubt, these will also be the ones with higher scores on the various sex egalitarianism scales, as most of the highly developed countries are inhabited mainly by Europeans. If one accepts that there is a general sexual dimorphism factor between populations, and that the height gaps are caused by genetic factors that vary by population, then we reach the conclusion that non-height sexual dimorphism also varies by population for genetic reasons

Oh and by the way, this study found that "We find evidence that human populations vary substantially and unexpectedly in both the magnitude and direction of facial sexually dimorphic traits. In particular, European and South American populations display larger levels of facial sexual dimorphism than African populations.", but they only had data for a few populations. Still, Europeans are usually sexually dimorphism even in physical phenotypes that are very hard to explain by something that isn't genetics.

Supporting this speculation, in a study of 76 nonindustrial societies, female work participation was negatively correlated with sexual dimorphism in height, thus a correlation between one aspect of sexual dimorphism (height) and another (division of labor). Of course, extrapolating this to other traits is conjecture, but interesting nevertheless.

Does the pattern hold for intelligence as well? I downloaded David Becker's dataset of national IQs, but it doesn't appear he collected the scores separately by sex. Richard Hanania plotted some of Lynn's sex difference data on the Wechsler for adults and it looks like this:

We don't have data for many counties, as most of the lines are different samples or editions of the test for the same countries. Better would be to gain access to some data from online testing sites with massive samples so that one can compute the sex difference by country. That would require that one assumes that the self-selection bias in these online samples (most people don't take online IQ tests) is not causing changes in the IQ sex gaps between countries. I don't know how plausible this is, but worth trying I guess.

Overall, it seems the genetic model is plausible. Some countries have larger sex differences in various kinds of measured psychological variables, and these appear to be largely the same with larger differences in height too. Such patterns can result from cultural or and other non-genetic causes, but it is also possible that different populations evolved differently sized sex differences. This model has not been given any attention in the literature as far as I know. I couldn't even find a paper that suggested the idea.

What research can be done? First, replicate the height gap analysis and see how well it actually correlates with the other sexual dimorphism data from other studies. In particular, check if this can 'just' be explained by population stratification / spatio-genetic autocorrelation. It seems one can download the data from here. It is not that clear from the data whether it's mainly Europeans who are extra sexually dimorphic across many traits (even eye and hair color!), or whether populations worldwide have a kind of general sexual dimorphism factor score

Second, the genetic model requires that the sex height gaps have been reasonably consistent over recent history, as they could not change that fast for genetic reasons. So using the height meta-analysis, it should be analyzed whether the countries with the largest sex gaps in the first year of data are the same as those in the last year. OWID has the data it looks like. It does appear this is roughly the case because height seems to have gained at about the same rate for both sexes. Since the gap here is computed as a ratio, men would have to grow slightly men for the ratio to stay constant.

As usual, if you want to get involved with this research project, just send me an email.