You may have read that having a male brain can make you a better leader or will earn you more money.
Or maybe that female brains are better at multitasking?
But the truth is that there is no such thing as a male-female brain.
The first search for sex differences across the entire human brain, reveals that most people have a mix of male and female brain features. And it also supports the idea that gender is non-binary, and that gender classifications in many situations are insignificant.
“This evidence that human brains cannot be categorized into two distinct classes is new and somehow radical,” says Anelis Kaiser at the University of Bern, Switzerland.
The idea that people have either a male-female brain is an old one, says Daphna Joel at Tel Aviv University in Israel.
To test this theory, Joel and her colleagues looked for distinction in brain scans taken from 1400 people aged between 13 and 80.
In total, the group find 29 brain regions that generally seem to be different sizes in self-identified males and females.
These include the hippocampus, which is involved in memory, and the inferior frontal gyrus, which is thought to play a role in risk aversion.
When the group looked at each individual brain scan, however, they found out that just few people had all of the brain features they might be expected to have, based on their sex. Across the sample, between 0 and 8 % of people had “all-female” or “all-male” brains, depending on the definition. “Most people are in the middle,” says Joel.
This means that, averaged across people, sex differences in brain structure do exist, but an individual brain is likely to be just that: individual, with a mix of features. “There are is no male-famail brain,” says Joel.
Although the team only looked at brain structure, and not function, their findings claim that we all lie along a continuum of what are traditionally viewed as male and female characteristics. “The study contribute in providing biological support for something that we’ve known for some time – that gender isn’t binary,” says Meg John Barker.
The findings will still come as a surprise to many, including scientists, says Bruce McEwen at the Rockefeller University in New York. “We are beginning to understand the complexity of what we have traditionally understood to be ‘male’ and ‘female’, and this study is the first step in that direction,” he says. “I think it will change peoples’ minds.”
Despite the stereotypes, girls are no worse than boys at science and maths subjects, either.
“People get wedded to the idea that having male female brain is highly predictive of having different aptitudes or career choices,” says Margaret McCarthy.
Alexandra Kautzky-Willer, head of the Gender Medicine Unit at the Medical University of Vienna in Austria, agrees that things aren’t so simple. “There are differences between women and men when you look in large groups, and these are important for diagnosis and treatment,” she says. “But there are always more differences within genders. We always need to look at environment, culture, education and a personal role in society,” she says.
If a neuroscientist was given someone’s brain without their body, they would still probably be able to guess if it had belonged to a woman or a man. Men’s brains are larger, for example, and are likely to have a larger number of “male” features overall. But the new findings suggest that it is impossible to anticipate what mix of brain features a person is likely to have based on their sex alone.
Joel predicts a future in which individuals are not classified based on gender alone. “We separate men and women all the time,” she says. “It’s wrong, not just politically, but scientifically, because everyone is different.”
But other scientists, don’t think that will ever be possible. As a sexually reproductive species, identifying a person’s biological sex will always be of paramount importance to us, they say.
After all, some people don’t identify themselves as either female or male, and others feel their gender identity shift over time. “It’s a shame that people’s experience alone isn’t enough for us to recognize as a society that non-binary gender is legitimate.”
“We need to start thinking more carefully about how much weight we give to gender as a defining feature of human beings, and stop asking for it in situations where it simply isn’t relevant,” says Barker.