“As soon as scientists could image the brain, they began hunting for sex differences…in the new study, researchers led by Daphna Joel, a behavioral neuroscientist at Tel Aviv University in Israel, tried to be as comprehensive as possible. Using existing sets of MRI brain images, they measured the volume of gray matter (the dark, knobby tissue that contains the core of nerve cells) and white matter (the bundles of nerve fibers that transmit signals around the nervous system) in the brains of more than 1400 individuals. They also studied data from diffusion tensor imaging, which shows how tracts of white matter extend throughout the brain, connecting different regions.
The majority of the brains were a mosaic of male and female structures, the team reports…Depending on whether the researchers looked at gray matter, white matter, or the diffusion tensor imaging data, between 23% and 53% of brains contained a mix of regions that fell on the male-end and female-end of the spectrum. Very few of the brains—between 0% and 8%—contained all male or all female structures. “There is no one type of male brain or female brain,” Joel says.
“There is no sense in talking about male nature and female nature,” Joel says. “There is no one person that has all the male characteristics and another person that has all the female characteristics. Or if they exist they are really, really rare to find.”
Study: Sex beyond the genitalia: The human brain mosaic (Proceedings of the National Academies of Science). From the abstract:
- Significance: Sex/gender differences in the brain are of high social interest because their presence is typically assumed to prove that humans belong to two distinct categories not only in terms of their genitalia, and thus justify differential treatment of males and females. Here we show that, although there are sex/gender differences in brain and behavior, humans and human brains are comprised of unique “mosaics” of features, some more common in females compared with males, some more common in males compared with females, and some common in both females and males. Our results demonstrate that regardless of the cause of observed sex/gender differences in brain and behavior (nature or nurture), human brains cannot be categorized into two distinct classes: male brain/female brain.
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