Smart money on a bigger male brain? Dangerous talk indeed

The male brain is bigger - so that means men are smarter, right?

Aside from being a dangerous thing to say among women, it is also wrong on both counts.

A major study of 1,400 male and female human brains has failed to find any evidence for “sexual dimorphism” - the official way to describe differences in size or appearance between the sexes, in addition to the sexual organs themselves.

Distinct variations in the male and female brain have been sought and claimed many times.

Less capable of reasoning?

These are often held up as examples of why women are inferior or less capable of reasoning, or why a woman might not deserve equal pay for equal work.

Claims for dimorphic differences are being dismissed out of hand by an international research team led by Daphna Joel of Tel-Aviv University and colleagues.

"Our study demonstrates that although there are sex/gender differences in the brain, human brains do not belong to one of two distinct categories: male brain/female brain," the authors write in the journal Proceedings of the National Academy of Sciences (PNAS), the scientific journal of the US National Academy of Science.

The researchers studied magnetic resonance images of 1,400 people from four data sets. In each group they found a subset of brain regions that differed the most between the sexes.

If these differences were more common in males they were described as being on the male end of the distribution, and if more common in females then they were at the female end.

Die-hard adherent

If you are a die-hard adherent to the dimorphic assumption, then you might expect to see all the male end differences clustered among the boys and girl variants bunched among the girls.

No such thing is the case, the researchers found. They found between 23 per cent and 53 per cent of brains had at least one male end region and one female end region.

The number of individuals with all male or all female brain subsets were much smaller, ranging from none at all to just 8 per cent, depending on the region, the authors found.

These people are very rare, they write. “Rather, most brains are comprised of unique “mosaics” of features”, some male, some female and some intermediate, they say in their research paper, Sex Beyond the Genitalia: The Human Brain Mosaic.