On sex differences in height and food discrimination (why the hypothesis is ridiculous)

We got critique from several academics for the tweet mocking a paper claiming gender difference in height might be due to gender oppression and food discrimination during evolution which resulted in sexually dimorphic gene expression making women shorter. Many fellow scholars and academics argued that the hypothesis was plausible and interesting and not worthy making fun of. We at @RealPeerReview disagree, the hypothesis makes no sense, lacks evidence and is basically impossible from a theoretical perspective. But since we got some civil critique from a blogger arguing that the paper has a point we decided to write a response to explain why we considered it worthy of featuring on our infamous timeline.

Sex differences in height

Sex differences in size is a well observed phenomenon across the animal kingdom. In mammals, and especially among primates, the larger sex tends to be the male. As darwinian theory predicts the male’s higher reproductive capacity (due to smaller gamete size and lower biological investment in reproduction) will lead to males having higher variance in reproductive success in most mammal species. This leads to more intense competition for mates among the males which selects for larger size (competition tend to be violent). Mammal females on the other hand having slower reproductive rate (males can impregnate several females under a short period of time while the reverse is much more difficult) will be favored by reaching sexual maturity earlier so they can start reproducing at an earlier age, this would select for smaller size. Since males have a much faster reproductive rate they can afford spending time to grow larger before starting to compete for mates, entering puberty too early would make them unable to successfully compete. And when they have grown large enough they can reproduce at such a fast rate (if they’re successful) it makes up for the time spent on growing those extra inches. This is why sex difference in height appear at puberty in most mammals including humans (at 12 years of age the average girl is actually taller than the average boy). This theory is well established and has been tested. Surely a new explanation for size dimorphism must in that case reveal serious flaws in this theory and provide new groundbreaking evidence no?

The problems with the hypothesis

There are several problems, first of all the main causal effect it proposes for sex difference in height in humans (women being systematically deprived of food) simply lacks evidence. Surely you can find cultures and villages where more girls suffer from malnutrition than boys but the opposite is also true. Thus there is simply no evidence for any food deprivation of females in human history on a global scale, and since sex difference in height is present in all cultures this food discrimination must have been global.

Also the paper doesn’t in any way manage (or even try) to debunk the established and tested explanation for sexual dimorphism in height among humans. It doesn’t make the case for why a new explanation is even needed. We do suspect though that some people would argue she doesn’t even try to explain the entire sex difference in height with this theory but just part of it. But even so the proposed explanation is actually quite ridiculous which brings us to our main point…

The hypothesis is simply impossible from an evolutionary perspective

Evolution is about maximizing your own fitness by leaving as many healthy descendants that survive until adulthood and themselves reproduce as possible. It’s not about a gender war where one sex tries to dominate and oppress the other. Does that mean that there was no way for males to enhance their own fitness at the expense of females? Of course there were, abusive behavior such as hindering females from mating with other higher quality males of their own choice (by restricting their freedom) and forced copulation are examples of sexual conflict where a male enhances his own fitness at the expense of female fitness (females can play this game too although they tend to prefer other methods).

None of these tactics however include reducing the female’s ability to bear healthy children since men need women to be fertile in order to have as many healthy children on their own. The point of her argument is that women should be taller because female fertility would increase if they were but that malnutrition (which by its own would reduce fertility even further) made them shorter. The problem is that if women increase their fertility by being taller it would increase male fertility as well. Men need women to have children if they are to have any children of their own since women are the bottleneck of reproduction due to their slower reproductive rate. Why would men interested in increasing their own fertility have any interest at all in reducing women’s ability to give birth to as many healthy children as possible?

The basis of her argument is simply that men for several millennia engaged in behavior that ultimately would reduce their own fitness on a global scale just for the sake of oppressing women. With no evidence to back it up. Since girls and boys are of equal height until sexual maturity this systemic male orchestrated food deprivation of women must have taken place during women’s childbearing years. By starving women men would not only have reduced a woman’s fertility and their own chance of making her pregnant but also damaged the health and future prospects of their own children by keeping their mothers malnourished during pregnancy. All this only for the sake of men longing to dominate women.

But evolution isn’t about a sex war, evolution doesn’t favor domination of the other sex for it’s own sake, evolution favors enhanced fitness. To propose that men have been oppressing women just for the sake of it, even when it reduces their own fitness, on a global scale for such a long time it has left a decisive mark on sexually dimorphic gene expression reeks of radfem paranoia. It’s the idea, so common in academic feminist theory, that everything is about domination, power structures and gendered oppression that now has been applied to explain evolutionary sex differences. It’s a theory that isn’t just lacking in any evidence but a theory that makes no sense at all. Cultural norms are mainly just extensions of behavioral traits and they are under selective pressure too. Fitness reducing behaviors are selected against, this type of behavior from males would have been strongly selected against.

Power structures can’t explain everything

Not all sex differences can be explained with power structures even though this idea is appealing to many academics on the left end of the political spectrum. Men have their faults and men have surely oppressed women during history, but oppression such as controlling women by restricting their freedom and ability to make their own mate choice (mate-guarding) and forced copulation (rape) could all be argued to have increased the individual man’s own fitness at expense of the woman (and rival males). Males conspiring to deprive their own wives and daughters of food so that they have problems becoming pregnant wouldn’t give any man any reproductive benefits at all. On the contrary. That’s why the hypothesis is crazy. That’s why we mocked the paper.

Please show us a society where men prefer to distribute food to unrelated males rather than their own starving wives and daughters. It doesn’t exist for the reason we mentioned, such men would be selected against. This is simply how evolution works.

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