They started with a set of MRIs that measured the volume of grey matter in the brains of 112 men and 169 women ages 18 to 79. On these scans, they examined 116 separate regions and zeroed in on the 10 that showed the greatest difference between men and women. In each case, the 281 scans were divided into three categories – one-third considered “most male,” one-third considered “most female” and one-third in the middle.
Only six per cent of the brains consistently ranked among the “most male” or “most female” in all 10 categories, the researchers found. On the other hand, 35 per cent showed “substantial variability,” with male traits in some regions and female traits in others.
The study authors then repeated the analysis with different cutoffs for being “most male” and “most female”. Regardless of whether they used a threshold of 10 per cent, 20 per cent or 50 per cent, the brains with a combination of male and female features far outnumbered the brains that were exclusively male or exclusively female.
Next, the researchers followed the same steps with other sets of brain scans that measured the thickness of grey matter in the outer layer of the cerebrum, the connections between different parts of the brain, and other features. As before, they found that consistently male or consistently female brains were rare, and brains with features related to both genders were common.
Finally, the scientists applied the same method to data from two large psychology studies of US teens. Using results from 570 participants in the Maryland Adolescent Development in Context Study, they found that only 1.8 per cent of them scored consistently male or consistently female, compared with 59 per cent who showed “substantial variability.” Among 4,860 participants in the National Longitudinal Study of Adolescent to Adult Health, the skew was even greater: 0.1 per cent versus 70 per cent.
Even in a data set of 263 university students who were asked about 10 “highly gender-stereotyped activities” like watching talk shows on TV or playing video games, the study authors still found that only 1.2 per cent of the students could be classified as exclusively male or exclusively female, compared with 55 per cent who had traits from both camps.
“This extensive overlap undermines any attempt to distinguish between a ‘male’ and a ‘female’ form for specific brain features,” Joel and her colleagues concluded. These findings have “important implications for social debates on long-standing issues such as the desirability of single-sex education and the meaning of sex/gender as a social category.”
So, this is exactly what the original theory predicts. That there’s a spectrum of brain types. Any one individual can have any of the types along the spectrum. All individuals are therefore to be treated entirely as individuals, just as any form of liberalism would insist.
However, the distribution of the types along the spectrum is not random when measured against sex (and yes, we’re talking dangly bits or not, not gender). We predict, and this research indicates, that certain characteristics are more likely to be connected with various genital arrangements. More likely: just as in the sense that men are generally taller than women but that John Bercow is a short arse doesn’t make him a woman (nor Sally Bercow a man because of her height).
So, what’s the headline to this?
There’s no such thing as a ‘male brain’ or ‘female brain,’ these scans show
The importance of this is that if we then make the next leap, one that I’m not going to try to attempt to prove here but one that sounds reasonable enough, that different brain types lead to different aptitudes for certain things, then we will find that those more likely to have the certain brain type, male or female, are going to be more likely to have aptitudes for certain things. We might even see clustering. Say, males among the Aspies who are good at coding, females among those with the empathy to be good at nursing.
The theory (and here the evidence) does not say that “men are good at coding, women are not”. It says that ” a certain brain type which is more common in men is good at coding”. Sex is only a proxy, and not a terribly accurate one, for the possession of the brain type.
The importance of this is that we cannot therefore look at the population of coders, note that it is mostly male, and thus conclude that females are being discriminated against. Any more than we can look at basketball teams and concludes that dwarves are being discriminated against (and wouldn’t that be a fun sport to try and set up? Dwarf Basketball, coming to a screen near you!).
It’s still entirely possible that those with the coding brain are discriminated against because of their plumbing arrangements. That would be bad and if it were true we would want to do something about it (like, employ all those cheap and good coders, a la Dame Stephanie Shirley). But the sex imbalance isn’t evidence of it being true: simply because we do have this finding that brain types, along that spectrum, are not equally distributed according to plumbing arrangements.