Do you have a male brain or a female brain? The answer, according to science, is no.
If you didn’t expect this to be a yes-or-no question, you’re not alone. Male brains do seem to be built differently than female brains. An analysis of more than 100 studies found that the volume of a man’s brain is 8% to 13% greater than the volume of a woman’s brain, on average. Some of the most noticeable differences were in areas of the brain that control language, memory, emotion and behavior, according to a 2014 report in the journal Neuroscience and Biobehavioral Reviews.
To find out whether these structural differences translated into cognitive differences, scientists examined detailed brain scans of more than 1,400 men and women. No matter which group of people they looked at, what type of scan was used or which part of the brain was examined, the researchers consistently failed to find patterns that set men and women apart.
To figure this out, the team – led by psychobiologist Daphna Joel of Tel Aviv University in Israel – went hunting for examples of brain “elements” that were either clearly male or clearly female. In other words, they looked for examples of measurements that appeared to cluster one way for men and another way for women, without much overlap in the middle. Then, after identifying these elements, the researchers looked to see whether women tended to have the “female” versions and men tended to have the “male” versions.
They started with a set of MRIs that measured the volume of gray matter in the brains of 112 men and 169 women ages 18 to 79. On these scans, they examined 116 separate regions and zeroed in on the 10 that showed the greatest difference between men and women. In each case, the 281 scans were divided into three categories – one-third considered “most male,” one-third considered “most female” and one-third in the middle.
The study authors then repeated the analysis with different cutoffs for being “most male” and “most female.” Regardless of whether they used a threshold of 10%, 20% or 50%, the brains with a combination of male and female features far outnumbered the brains that were exclusively male or exclusively female.
Next, the researchers followed the same steps with other sets of brain scans that measured the thickness of gray matter in the outer layer of the cerebrum, the connections between different parts of the brain, and other features. As before, they found that consistently male or consistently female brains were rare, and brains with features related to both genders were common.
Even in a data set of 263 college students who were asked about 10 “highly gender-stereotyped activities” like watching talk shows on TV or playing video games, the study authors still found that only 1.2% of the students could be classified as exclusively male or exclusively female, compared with 55% who had traits from both camps.
“This extensive overlap undermines any attempt to distinguish between a ‘male’ and a ‘female’ form for specific brain features,” Joel and her colleagues concluded. These findings have “important implications for social debates on long-standing issues such as the desirability of single-sex education and the meaning of sex/gender as a social category.”
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