One distressing characteristic of the Left, at least as far as science is concerned, is to let our ideology trump scientific data; that is, some of us ignore biological data when it’s inimical to our political preferences. This plays out in several ways: the insistence that race doesn’t exist (and before you accuse me of saying that races do exist, read about what I’ve written here before: the issue is complex), that there are no evolutionarily-based innate (e.g., genetically based) behavioral or psychological differences between ethnic groups, and that there are no such differences, either, between males and females within humans.

These claims are based not on biological data, but on ideological fears of the Left: if we admit of such differences, it could foster racism and sexism. Thus. any group differences we do observe, whether they reside in psychology, physiology, or morphology, are to be explained on first principle as resulting from culture rather than genes. (I do of course recognize that culture can interact with genes to produce behaviors.) This ideological blinkering leads to the conclusion that when we see a difference in performance between groups and genders, the obvious explanation is culture and oppression, and the remedy is equal outcomes rather than equal opportunities. Yet in areas like most sports, where everyone agrees that males are on average larger and stronger than females, it’s clear that the behavioral differences (i.e., performance) result from biological differences that are surely based on evolution (see below). In sports like track and field or judo, nobody would think of making males compete with females.

But that’s not a good way to act. The Left has historically been characterized by respect for the facts, and the refusal to even consider that such differences could be based in part on genes is an unwelcome and unhealthy departure from our traditional embrace of rationality. Yes, phony biological data has been used to support racism and sexism, but remember that that is the fault of human prejudice, cooked data, and an inability to do proper experiments that have all resulted in terrible data being used to support human prejudices. Finally, of course, culture can influence behavior, including reinforcing biologically-innate behaviors if they are seen as “normal.”

To claim that there are no evolutionary differences in behavior and psychology between men and women is fatuous. The data show otherwise, though of course for most traits we don’t know if it’s genetic. But the default hypothesis, based on observation of other species (especially primates) is that at least some psychological and behavioral differences will be based on genes that evolved via selection in our ancestors. Why is the brain immune to evolved, sex-specific differences but the body is not?

Thus, to claim, as does P.Z. Myers in a new post, that higher testosterone levels in males have minimal influence on their aggressiveness compared to the effects of culture, is a claim based not on data—which show that he’s wrong—but on ideology. And so he and his commenters try to refute the testosterone-effect notion using anecdotes: some males aren’t aggressive, Myers himself is not aggressive (!), aggression is due “mostly” to cultural difference (the “patriarchy”) rather than to biological differences, and so on. To read the comment thread is to see a bunch of progressives desperately squirming to avoid the obvious.

Well, I’m not an expert on testosterone, but what I do know is that levels of that hormone are not only correlated with aggression within and among the sexes, but that injecting it into both men and women also makes their behavior and psychology more aggressive. Thus the correlation at least partly reflects causation.

But let’s look at some data showing prima facie that there are biological differences in behavior between males and females, and that those differences reflect the working of natural selection—in the form of sexual selection—in our ancestors. To do this, we’ll use body size as an index of behavior. I’ll try to be brief.

It’s well known that in virtually all species of primates (there are a few exceptions in lemurs), and in other groups such as pinnipeds, males are larger than females. That is not cultural, but genetic; if you rear gorillas in any habitat, the males are going to grow up larger than females. You can see the data among species yourself in a 2006 paper by Adam D. Gordon (reference and free link below), showing an almost universal trend for the male/female body mass to be larger than 1 in primate species (in every species there are of course some small males and large females, but we’re talking about averages).

Why is this? It reflects evolved male behavior: the tendency of males to compete for females, and the advantage of large body size in that competition. Whether the advantage be in direct competition, so that the larger you are the more you can fight off other males (gorillas, elephant seals), or in female choice, so that females choosing large males can gain protection for her young from marauding males (also gorillas), the difference in size reflects something almost universal among animals: males, who have cheap gametes, must compete for females who have expensive gametes and invest more in reproduction. And that is why, in study after study in humans, male sexual behavior shows promiscuous mating, while females are more selective. That’s not necessarily all biological, but some of it surely is given that our closest relatives show the same behaviors and that there is no such thing as The Gorilla and Chimpanzee Patriarchy.

Here’s further evidence that the larger size and strength of males is reflected in their behavior—and was almost certainly promoted by sexual selection:

In human societies studied by Richard Alexander, those societies that are more polygynous (in which males compete more intensively for females) show greater sexual size dimorphism than societies that are more monogamous. This was a prediction made before the data were acquired—a prediction derived from sexual selection theory. And it was fulfilled.

Among species of primates, there’s a good correlation between the polygyny of a species and sexual dimorphism: those species in which males have a higher variance in offspring number, and in which males thus compete more intensely for females, also show a greater ratio of male/female body size, even when corrected for phylogeny. (Too, in primate species in which males fight each other over females, the relative size of the canine teeth, used in battle, is larger than in species showing less direct male-male competition.)

In humans, as in many other species in which males compete for females, the sex ratio at birth favors males. They then die off at a higher rate due to higher risk-taking and exploratory behavior, until at reproductive age (about 25), the sex ratio is equal. Then, as males continue to die off, the sex ratio reverses, becoming female-biased at greater ages. This is exactly what evolutionary theory predicts: if there are biological differences in mortality rates, then evolution will adjust the sex ratio so it’s equal at the time of reproduction.

In line with the above, in humans and other primates, males show from the outset great exploratory and risk-taking behaviors, and as adults show many other behaviors that differ from those of females, such as greater dispersal. Is this due to the Primate Patriarchy? Probably not, given that these differences in behavior are shown in many species besides ours and make evolutionary sense.

As I said, some of this is in our own species may be due to culture, for culture can reinforce pre-existing biological differences that have come to be seen as “natural.” (I don’t need to emphasize here that I don’t think that what is “natural” in other primates, or what has evolved in our own species, should be accepted as the right way to behave!). Further, some have suggested that the size differences between men and women reflect ecological rather than reproductive differences—say in foraging behavior. But the data don’t support that, and they do support predictions made from the sexual-selection hypothesis. And even if ecology does play a role, that still reflects evolutionarily produced changes in some aspects of behavior.

All this is to say that body size is a proxy for behavior in our own group—primates—and that body size correlates with behavior: sexual behavior. To deny that the differences between human males and females in size and strength are evolved is to deny at the same time that differences in behavior between males and females is evolved. Only the blinkered ideologue would do that. Sadly, these ideologues continue to promote antiscientific ideas on the Internet.

I am not making claims here about other behaviors differing among the sexes, since there are no morphological correlates with other behaviors as clear as that between body size and sexual behavior. But the male/female difference in body size does reflect differences in psychology—psychology of mate acquisition. This alone shows an evolutionarily-based difference between men and women, one that is almost certainly does not rest entirely on culture, for we see the same differences in species lacking our culture. There is no Primate Patriarchy outside our own species.

And if all this be true, then it would be foolish to deny prima facie that there are other evolved differences in psychology between men and women, some reflected in morphology (why are men hairier than women?). The conventional wisdom should never be that men and women are biologically identical in their psychology and behavior, amiable as that may be to Leftist ideology. The primacy rests not with ideology, but with data; and while we can act against what the evolutionary data tell us (as we do when we use contraception), we should not deny that the data exist, or exercise confirmation bias so we try to dismiss data that contravene our ideology while welcoming data that support it. What we need to do is accept the data, but then adjust our society so that we realize the outcomes we want from our (partly evolved) morality. And that doesn’t mean structuring our society so that morality parallels biology.

And you can bet your tuchas that the ideologues will do their best to undercut (or ignore) the data adduced above. And for similar arguments but a lot more data, see Steve Pinker’s book The Blank Slate, which has a new Afterword with a detailed update on gender.

h/t: Steve Pruett-Jones

________

Gordon, A. D. 2006. Scaling of size and dimorphism in primates II: Macroevolution. Int. J. Primatol. 27:63-105.