I know there are some structural differences. But what do those differences
mean? What behaviour has been proven to differ because of them? The UPenn study is only actually examining a tiny, miniscule minority of brain connections; it's looking at adolescents (boys and girls mature at different rates), with no compensation for things like brain size.
Let's take hydrocephalus, a condition where the fluid-filled areas of the brain are abnormally large and the grey and white matter of the cerebrum correspondingly reduced. Some people with extreme hydrocephalus (where brain mass is about a tenth of normal) are, understandably, severely mentally impaired. But about half of them actually have normal behaviour and IQs averaging over 100, much like the non-hydrocephalic population. How do we make sense of this, that people can have such a huge difference in brain structure and be behaviourally normal, and at the same time that other people also with a similar huge difference from normal, are so different?
I don't presume to supply an answer, because I don't think we have one. But I do think that until there are sufficient experiments that prove a difference in behaviour based on an anatomical/phsyliological difference, we're never doing any more than hypothesising. A lot of hypotheses are wrong.
Okay, this a gross simplification of complex scientific argument muddled through simplicities in order make things digestable and engaging to the public.
The idea of male and female brains goes back a very long way. Men and women acted differently in society, so it was assumed they must have different brains. Charlatans a century or more ago claimed (wrongly) they could identify a brain as male or female just by looking at one (presumably removed from a dead body) and its gross features. So this has been a common baseline assumption rumbling along for generations, despite never really having a solid basis. The idea women and men might differ in large part because of the way they were brought up and the social roles they were squeezed into wasn't equally considered. Social roles were assumed to be the product of different behaviour from different brains.
Let's skip forward a long way into the era of neuroimaging, where possibly the most useful start point might be Simon Baron-Cohen, mostly known for autism research, who defined brains as "systematising", "empathising", or "balanced". He then popularised the notion that the "male" brain is systematising (autism being ultra-systematising), and the female brain empathising. Now, he didn't say "male" and "female" brains in his academic publishing, but he and others did pass that notion on to the public. He wrote a book "The Essential Difference: Men, Women and the Extreme Male Brain" (which might be more accessible to read than his hard science articles for non-experts). Thus from him and others, with weight from centuries-old assumptions, people latched onto this idea that gender differences were true and provable by anatomical/physiological studies. As for the inaccuracy of this male/female distinction, it is there in Baron-Cohen's research itself: whilst men
mostly have systematising and women
mostly empathising brains, it is far from absolute. (Incidentally, the idea of autism as being extreme male is also very dubious.)
Subsequent experiments show all sorts of extreme complications in trying to define "male" and "female" brains. To give one example of many (and bearing in mind almost no scientific papers should be considered the final word), try the one below as it's a relatively well known one. The long and short of it is, as I said, that I just don't think we know anything like enough to make firm conclusions.
Sex/gender differences in the brain are of high social interest because their presence is typically assumed to prove that humans belong to two distinct categories not only in terms of their genitalia, and thus justify differential treatment of males and females. Here we show that, although there...
www.pnas.org
Hope this helps.