In confrontation to centuries of conventional wisdom, a new study reveals that male and female brains are not biologically different. Any dissimilarities are culturally imposed.

Many studies of the past have suggested that a male brain is built differently and is anywhere from 8-13 percent larger than a female brain, most likely do to the increased testosterone levels necessary for the fetus to develop testicles. In particular, many believed that the male brain has superior control over language, and memory, while females have more developed areas relating to emotion and behavior.

Yet recently, a team of scientists from the University of Tel Aviv has performed over 1,400 brain scans of men and women and could not find any noticeable difference. No matter what type of scan they used, what part of the brain the examined, or which group of people they looked at, they could find not any discernible pattern that distinguished male and female brains.

“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,” said the team in the study they published in the Proceedings of the National Academy of Sciences. “Each brain is a unique mosaic of features, some of which may be more common in females compared with males, others may be more common in males compared with females, and still others may be common in both females and males.”

The researchers spent months ‘hunting’ for traits that could clearly be described as either male or female. They searched for elements that seemed to cluster in a certain way in a male brain and a different way in a female brain; they sought distinctions that did not overlap.

In their first trial, they conducted MRI scans of 281 brains – 112 male, 169 female – to measure the volume of gray matter. In addition, they looked closely at 116 cerebral regions, paying particularly close attention to the 10 regions most suspected of showing gender differences.

Depending on what they saw, they would rate the brain as ‘most male’ ‘most female’ or a combination of the two genders.

In the end, only six percent of brains fell into the ‘most male’ or ‘most female’ categories. 35 percent of brains showed substantial variability in which regions demonstrated male or female traits.

To confirm their findings, the team repeated the experiment several times, increasing the threshold for a region to qualify as ‘most male’ or ‘most female’ with each round of scans. Yet even when the bar was set as low as 10 percent, brains that featured a combination of male and female traits always outnumbered ‘most male’ or ‘most female’.

Curious, the Tel Aviv team began to expand upon the features they looked at, now inspecting such qualities as the thickness of the outter layer of the cerebrum and the connectivity between various parts of the brain. Still, wholly one gendered brains were very rare.

Finally, the researchers turned to psychology by measuring data from two large studies conducted on American teenagers. The first, the Maryland Adolescent Development in Context Study, had 570 participants. Of those, only 1.8 percent scored consistently male or female while 59 percent showed substantial variability.

The second study, the National Longitudinal Study of Adolescent to Adult Health, included 4,860 participants. The results showed 0.1 percent were gender specific, 70 percent were combinations.

“This extensive overlap undermines any attempt to distinguish between a ‘male’ and a ‘female’ form for specific brain features,” the study concluded. The results of this study 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.”