Three More Lines of Evidence for Innate Sex Differences
An excerpt from my forthcoming book, A Billion Years of Sex Differences
This is the thirteenth excerpt from my forthcoming book, A Billion Years of Sex Differences. You can access the full collection here, and preorder the book here (UK) or here (US).
In the previous post, we looked at the first three of six lines of evidence that a given sex difference has an innate component: emergence in early childhood or at puberty, stability over time, and persistence despite socialization in the other direction.
This post covers the remaining three:
Hormonal evidence: Is prenatal or pubertal hormone exposure associated with sex-typical behaviour?
Cross-cultural evidence: Do the same sex differences show up across societies with different norms, values, and institutions?
Cross-species evidence: Do we see the same differences in other animals with a similar evolutionary backstory to our own?
As before, none of these lines of evidence is decisive. But when many independent lines converge on the same conclusion, it becomes harder and harder to dismiss them.
Three More Lines of Evidence for Innate Sex Differences
4. Hormonal Evidence
Many of the standard-issue sex differences have been linked, at least tentatively, to hormones such as testosterone and estrogen. Contrary to popular belief, the links between people’s current hormone levels and sex-typical behaviour are weak: People with higher testosterone aren’t necessarily more aggressive or competitive, for example. In contrast, the links between prenatal hormone levels and sex-typical behaviour are often fairly strong.
One line of evidence for this comes from individuals with DSDs – that is, disorders (or differences) of sexual development. The most famous of the DSDs is congenital adrenal hyperplasia, also known as CAH. Individuals with CAH are exposed to high levels of androgens in the womb. For males, this makes little difference, as males are normally exposed to high prenatal androgen levels. For females, however, it’s a game-changer. The surplus androgens partially masculinize females’ bodies – and, it seems, their minds. As children, girls with CAH tend to be less interested in dolls and other female-typical toys, and more interested in so-called boys’ toys. They’re also less interested in babies or having children, and often have more male-typical interests and career aspirations. As adults, women with CAH are more likely to be sexually attracted to other women and often end up in male-typical jobs. Their gender-atypical behaviour doesn’t seem to be a result of being socialized to be more masculine. On the contrary, some evidence suggests that CAH girls act in male-typical ways even when their parents encourage them to act more like stereotypical girls. In other words, prenatal hormones sometimes trump postnatal socialization.