Thread by @WiringTheBrain

Neurosexism: the myth that men and women have different brains nature.com/articles/d4158… - this battle of extreme positions obscures the more nuanced and realistic position of an interplay between biology and culture

It is absurd to think that there are no biological differences between male and female brains in humans, as there are in every other species, for very good evolutionary reasons. But...

...It is perfectly right to challenge findings from poorly done neuroimaging studies and especially to challenge their over-interpretation. But...

....There are now much better, much bigger studies that continue to show sex differences in neuroimaging parameters. Even if these were all related to overall body size and brain size, that is still a difference. And...

...Even if neuroimaging found NO differences between male and female brains that wouldn't mean there are none. Neuroimaging can only detect differences on a macro scale. There are diffs on microanatomical scale and even in gene expression b/w male and female cells. But...

...We don't know the effects of most such differences. Apart from sexual preference (and arguably physical aggression), we shouldn't expect two categorical types - either in brain anatomy or in behaviour

But not having two distinct types doesn't mean a group difference isn't real. See: height. Sex diffs can be small, relative to variation for other reasons (just general individual differences), but still real.

While it is absurd to deny the existence of brain diffs b/w males and females, it is equally absurd to think such biological diffs explain all the observed diffs in behaviour. Cultural effects are also clearly very strongly at play.

For more, see chapter on sex differences in Innate: press.princeton.edu/titles/13255.h…

As a general point, to have this discussion with no mention of findings from other species, from which we evolved, is really bizarre. We did not spring, as a species, fully formed from the head of Zeus.

We're mammals. We're primates. We're not somehow exempt from the extremely strong forces of sexual selection that have led to sex differences across these groups (in all animals, actually). Nor could we erase that history.

One example of a well designed neuroimaging study looking at sex diffs in brain structure: Machine learning of brain gray matter differentiates sex in a
large forensic sample rdcu.be/boO2M

This study has large numbers, good agreement in areas showing diffs b/w males and females b/w two independent samples, prediction tested in separate test samples in each case - very strong methodology

And it finds, as other studies have, some areas are larger on females and some are larger in males, which means the differences are not accountable for just in terms of overall brain size

Should have said: HT @SeveriLuoto - thanks!

Important caveats: 1. these are group average diffs in overall profile but any individual will match the overall M or F profile more or less closely and there will be much more variability for individual parameters

2. we don't know if these differences have ANY consequences for behaviour, or what they might be. (And there is no suggestion that one form is somehow better than the other)

3. we don't know from imaging adults what caused these differences. They could be driven by biological factors leading to the masculinisation or feminisation of brain structures during development and maturation...

...or they could be driven (in theory at least) by the differences in experience that boys and girls and men and women have in society

A prediction of the biological origin would be that very young infants would also show sex differences in their brains, prior to any possible impact of enculturation. (They needn't be exactly the same and more might arise over maturation)...

As found here, for example: Investigation of brain structure in the 1-month infant ncbi.nlm.nih.gov/pubmed/29305647

I've been advised of an important correction to that article here: link.springer.com/article/10.100… In which they show that the regional differences were miscalculated, though the overall volume diffs remain

This one is better, I think (but who knows, may have its own problems): Impact of sex and gonadal steroids on neonatal brain structure ncbi.nlm.nih.gov/pubmed/23689636