For many years, society has declared the structure of the human brain so different according to gender, we’ve even managed to convince ourselves that the male and female specimens derive from entirely different parts of the solar system. But now, according to science, our biological makeup may not be so far apart after all.

A new study, published by the Proceedings of the National Academy of Sciences on Monday, has found that while specific parts of the brain show some differences according to sex, an individual brain only rarely has all “male” traits or all “female” traits.

Researchers claim the human brain is more likely to contain a diverse array of attributes: some things will be more common amongst women, others amongst men, while some will be common in both. The research also supports the idea that gender is non-binary, meaning that gender classifications in many situations are completely futile.

This argues against the idea that brains can be neatly divided into sex-based categories, something Daphna Joel of Tel Aviv University, along with co-authors of the study, have argued for a long time. “The theory goes that once a foetus develops testicles, they secrete testosterone which masculinises the brain,” says Joel, “If that were true, there would be two types of brain.”

The study used MRI scans of more than 1,400 brains, with a focus on their anatomy rather than how they function. Scientists then scored variable traits such as thickness of tissue or volume in different parts of the brain. They concentrated on traits that showed the biggest sex differences, separating the scores into a primarily male zone, a primarily female zone, and an intermediate range.

The key question researchers wanted to answer was how often did a brain end up in just a single category? The answer turned out to be not often, since scientists generally found this happened in 6 percent or less of brains across analyses of several sets of data.

Researchers discovered it was much more likely for an individual to score in both the male and female zones than to show in a line-up indicating one clear sex.

Overall, the results demonstrate that “human brains do not belong to one of two distinct categories” male and female, researchers have concluded.

Larry Cahill, neuroscientist at the University of California, Irvine, who did not participate in the study, said he agrees that brains contain a diverse mixture of male and female anatomical traits, but that doesn’t discount variations in how brains of the two sexes function.

There’s “a mountain of evidence proving the importance of sex influences at all levels of mammalian brain function,” he said.

That work shows how much sex must matter, “even when we are not clear exactly how,” he wrote in an email.

Additional Reporting by Associated Press.

Image via Shutterstock.

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