Many of you know that the topic of sex differences in psychology is fraught with controversy. It's an area where people, for many decades, didn't really want to enter because of the risks of political incorrectness, and of being misunderstood.
Perhaps of all of the areas in psychology where people do research, the field of sex differences was kind of off limits. It was taboo, and that was partly because people believed that anyone who tried to do research into whether boys and girls, on average, differ, must have some sexist agenda. And so for that reason a lot of scientists just wouldn't even touch it.
By 2003, I was beginning to sense that that political climate was changing, that it was a time when people could ask the question — do boys and girls differ? Do men and women differ? — without fear of being accused of some kind of sexist agenda, but in a more open-minded way.
First of all, I started off looking at neuroanatomy, to look at what the neuroscience is telling us about the male and female brain. If you just take groups of girls and groups of boys and, for example, put them into MRI scanners to look at the brain, you do see differences on average. Take the idea that the sexes are identical from the neck upwards, even if they are very clearly different from the neck downwards: the neuroscience is telling us that that is just a myth, that there are differences, even in terms of brain volume and the number of connections between nerve cells in the brain at the structure of the brain, on average, between males and females.
I say this carefully because it's still a field which is prone to misunderstanding and misinterpretation, but just giving you some of the examples of findings that have come out of the neuroscience of sex differences, you find that the male brain, on average, is about eight percent larger than the female brain. We're talking about a volumetric difference. It doesn't necessarily mean anything, but that's just a finding that's consistently found. You find that difference from the earliest point you can put babies into the scanner, so some of the studies are at two weeks old in terms of infants.