Scientists Still Unable to Identify Major Sex Differences in Human Brains

After more than a century of searching, scientists are still unable to come up with any major sex differences in human brains, according to The Conversation.

The academic nonprofit reports that scientists have been looking for differences between male and female brains since at least the 19th century.

Early on, scientists argued the size of the brain leads to greater intelligence. But that theory has been largely tossed out, the outlet reports.

Scientists have found the largest and most consistent brain sex difference to be located in the hypothalamus, which is responsible for regulating reproductive physiology and behavior. Researchers have found that at least one hypothalamic subdivision is larger in both male rodents and humans. But beyond reproductive differences, researchers were looking to identify causes in the brain of supposed sex differences in thinking.

Research then shifted to the cerebrum, which is responsible for intelligence, specifically the corpus callosum, a thick band of nerve fibers that carries signals between the two cerebral hemispheres.

The outlet reports that in the 20th and 21st centuries, some researchers found that the whole corpus callosum is proportionally larger in women on average, while others found that only certain parts are bigger. Some researchers thought that could be the cause of cognitive sex differences.

But smaller brains have a proportionally larger corpus callosum regardless of sex, and studies of this structure’s size differences have not been consistent, according to The Conversation.

Overall, brain studies trying to explain cognitive sex differences have not revealed any major discoveries, according to the outlet.

The Conversation also reports that learning can change the brain, which means human brain sex differences can’t be assumed to be innate. The brain can be changed through gendered culture, which is influenced by parenting, education, expectations and opportunities that differ based on sex.

Any sex differences in human brain structures are likely due to a combination of genes, hormones and learning, according to The Conversation.

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