Sex differences in behaviour do not require “hard-wired” brains

They merely require strategic responses to differing constraints.

(Note on usage: Sex is biological—i.e., which gametes a body is structured to produce. Sex roles are the behavioural manifestation of sex. Gender is the cultural manifestation of sex.)

Adult human males have, on average, about twice the lean upper body mass of adult human females. This means that adult human females have, on average, 52 per cent of the upper body strength of adult human males.

The consequence of this is that men dominate violence between adults. They dominate victims—another male is far more likely to be a physical threat or obstacle than a woman. Men even more strongly dominate perpetrators.

A Swedish study found that one per cent of the population committed almost two-thirds of all violent crimes. That one per cent was almost entirely male. Four per cent of the population committed all the violent crimes. That four percent was over [almost] 90 per cent male¹ and constituted just over seven per cent of the male population.

Source: Tim Mossholder, Unsplash.

These patterns of behaviour do not require any “hard wired” differences by sex in human brains. They merely require that men have about twice the upper body strength of women. They represent strategic behaviour within that context.

Indeed, these results are not compatible with sex-differentiation being strongly “hard-wired” in brains by sex. The overwhelming majority of men do not commit any violent crimes, while some of the perpetrators—just over seven [almost eleven] per cent—were female.

What makes it even clearer that these patterns represent strategic behaviour—that is, responses grounded in (biological) constraints and capacities—is that men and women each make up about half the perpetrators of violence against children.

When women are dealing with the physically stronger sex, they are much less likely to use violence than is the physically stronger sex. When they are dealing with a systematically weaker group of Homo sapiens—children—they are as likely to be perpetrators of violence as men.

These patterns represent strategic behaviour. They represents actions responding to constraints and capacities. You get sex-differentiated patterns when the constraints are different between men and women. Our sex-differentiated biology is enough, on its own, to produce sex-differentiated patterns of behaviour.

So, even in (then) peaceful Sweden, one in 14 men are violent. That a significant proportion of men are violent predators informs female behaviour, as the systematically physically weaker sex.

Men dominate sexual violence because they are physically stronger, have penises and cannot get pregnant. That is enough to have men dominate sexual violence without any sex differentiation in the “hard-wiring” of brains at all.

We are embodied agents. How we are embodied makes a difference for our behaviour.

Women have, on average, half the lean upper body mass as men not so much because they are smaller—the average differences in height and weight are nowhere near as large. A much more significant factor is that women have a higher fat content to their body, especially their upper body.

They have a higher fat content because human brains are energy hogs, and women are structured to be able to support not just one, but two or more, energy-hog brains—i.e. babies and toddlers. More fat means more readily-available stored energy. That extra female fat enables us Homo sapiens to be the most body-shape dimorphic of the primates: far more so than any of our ape cousins.

This goes to the other biological constraint that produces sex-differentiated behaviour. Women can get pregnant, men cannot. The risk profile differs for men and women, and not just for the risks of pregnancy and childbirth but also for child-rearing.

There will be different selection pressures on the male and female expression of genes as what they have to navigate to successfully reproduce differs. This includes selection for different hormonal patterns.

Hormones affect capacities and behaviour. So, difference in hormones between men and women will lead to differences in patterns of behaviour, again without requiring any “hard-wired” sex-differentiated differences in human brains to produce those differences.

Of course, hormones can also affect brain development. But that goes to the plasticity of human brains rather than pre-set “wiring” differences. Hence we get tendencies of varying intensity far more than absolute differences. We get male-typical behaviour that nevertheless does not only occur among males, or even among all males, and female-typical behaviour that also does not only occur among females, or among all females.

Biologically expensive children

Homo sapien children are remarkably biologically expensive, which has created very specific selection pressures. It takes a foraging child almost 20 years to achieve subsistence adulthood—that is, be able to forage as much food as they consume.

This is driven by us being a bipedal, tool-using species needing to learn how to make and use tools so as to hunt and gather without claws or rending teeth. Bipedal pelvises limit the size infant skulls can be. This means that childbirth is unusually risky for human mothers. It also requires postponing much brain development to after birth—hence human babies being so helpless and human children being so biologically expensive.

Human child-rearing is therefore a rolling series of almost 20 year projects. Hence, there was a strong reproductive advantage in women surviving 15-20 years beyond the birth of their last child, so after menopause. Hence us being the longest-living ape, with the longest childhoods—or, rather, being the longest-lived ape because our children have the longest childhoods.

This creates the need to transfer risks away from child-rearing—overwhelmingly to men. Hence men being so systematically stronger than women. Hence also selection for team work among males. Much of human dimorphism is driven by men and women confronting overlapping, yet also different, risk patterns.

Unmarried males in forager societies regularly provide food for women and children not their own. Such sharing provides a form of risk-management for when they may be unsuccessful in hunting, or be sick or injured. It also advertises their value as a provider.

For the other process required to raise our biologically expensive children is to transfer resources to child-rearing—overwhelmingly, [in foraging societies] from men.

Homo sapien fathers provide more care to their offspring than any other mammals. This creates more congruence in the reproductive incentives for Homo sapien mothers and fathers than in any other mammal species. But, as we have seen, more congruence is not complete congruence.

As the physically weaker sex selected to be able to manage bubs in tow, women are more likely to see emotions as a threat, be more concerned with emotional signs of commitment, to hide their aggression—including from themselves—to use stigma to enforce supportive behaviour, and as a mechanism of social leverage, and to focus on people and social connections.

As the physically stronger sex, using technology more aggressively, and needing to operate in teams, men are more likely to be direct in their aggression, use “ragging” to test team-mates (will you support me if things get tough?), and be more focused on things and systems. Hence mothers tend to attend more to emotions and inward family concerns, fathers more to capacities and dealing with the outside world.

All of these are tendencies to be more so. They are not absolute differences. None of them require much—or often any—sex-differentiated “hard-wiring” of human brains. Instead, what we see are overlapping patterns.

Yes, about 70 per cent of each sex has a pattern of personality traits not seen in the other sex, so we are a cognitively dimorphic species. But, given this result applies across 15 personality traits, a person only has to be outside the range of the other sex in one trait to produce this result.

Still, it is entirely possible to have a personality trait manifesting outside the range of the other sex. Hence the aforementioned level of cognitive dimorphism.

There are different patterns in behaviour by sex. But not rigidly differentiating patterns, outside the biological processes of reproduction.

Embodied actors

The notion that sex differences in behaviour between men and women are (only) socially constructed is obvious nonsense, as we are embodied strategic actors and the bodies of men and women are systematically different. This creates sex-differentiated constraints and possibilities, which creates sex-differentiated patterns of behaviour.

There are clearly differences between societies in their patterns of male and female behaviour, but that is because there are differences in constraints and possibilities in different societies, hence the behaviour patterns of strategic agents—specifically, of humans—will be different. But they are different in contexts that includes differences in the biological constraints inherent in being embodied actors who are members of a sexually dimorphic species. Indeed, differentiation in choices and cognitive development by sex tends to be higher in more gender-egalitarian countries—that is, in societies that are less constraining, leaving folk freer to follow their own preferences.

The social is emergent from the biological. It is not divorced from it.

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1. The text of the paper and the summary table have different numbers for female offenders. As the text states that 10.9 per cent of offenders were females, which agrees with the table but not the figures given in the text, I have corrected accordingly. Fortunately, it does not affect the logic being presented.