Can You Tell Which Brains Are Male? Neither Can These Scientists

The volumes (green = large, yellow = small) of brain regions in 42 adults, showing the overlap between the forms that brains of females and brains of males can take. Image courtesy of Zohar Berman and Daphna Joel. / Tel Aviv University

Scientists who tried very hard to find differences between male and female brains said they couldn't do it — not with brain scans and not even by asking seemingly obvious questions such as whether someone likes boxing or worries about his or her mother.

They couldn't find any single pattern that distinguishes between a male brain and a female brain, and say only a very small percentage of people fall under clear all-male or all female brain patterns.

"Our study demonstrates that although there are sex/gender differences in brain structure, brains do not fall into two classes, one typical of males and the other typical of females, nor are they aligned along a 'male brain-female brain' continuum," Daphna Joel of Tel Aviv University and colleagues wrote.

In fact, they found, most people are somewhere between clichéd ideas of male and female when it comes to brains, they said.

Joel's team looked at magnetic resonance imaging (MRI) scans of the brains of more than 1,400 people of all ages from around the world, including Americans, Chinese, Germans and Australians.

They did find some regions of the brain that tended to indicate sex differences. But when they considered these regions together across all their brain scans, the picture just got muddy, they reported in the Proceedings of the National Academy of Sciences.

Anywhere between 23 percent and 53 percent of the MRIs had at least one region with a "male-end" score and one region with a "female-end" score, they found. And at the most, 8 percent of the brain scans showed someone whose brain regions all scored "male" or "female."

"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," they wrote.

Other researchers have found some of the seemingly clear differences between male and female brains may be cultural rather than biological -- spatial sense, for instance.

Just to be really certain, they looked at a study of 157 women and 106 men done at a large Midwestern university that was designed to tease out sex differences in thinking. It included subjects such a gambling, housework, playing golf, watching porn or cosmetics that could be considered about as stereotypical as possible when it comes to gender differences.

Even there, they couldn't find a consistent pattern that predicted whether someone was male or female.

"In other words, even when considering highly stereotypical gender behaviors, there are very few individuals who are consistently at the 'female-end' or at the 'male-end', but there are many individuals who have both 'female-end' and 'male-end' characteristics," they wrote.