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Male and Female Brains are the same. Century Long Research Unable to Prove Otherwise

People have searched for sex differences in human brains since at least the 19th century, when scientist Samuel George Morton poured seeds and lead shot into human skulls to measure their volumes. Gustave Le Bon found men’s brains are usually larger than women’s, which prompted Alexander Bains and George Romanes to argue this size difference makes men smarter. But John Stuart Mill pointed out, by this criterion, elephants and whales should be smarter than people.


So focus shifted to the relative sizes of brain regions. Phrenologists suggested the part of the cerebrum above the eyes, called the frontal lobe, is most important for intelligence and is proportionally larger in men, while the parietal lobe, just behind the frontal lobe, is proportionally larger in women. Later, neuroanatomists argued instead the parietal lobe is more important for intelligence and men’s are actually larger.


In the 20th and 21st centuries, researchers looked for distinctively female or male characteristics in smaller brain subdivisions. Nonetheless behavioral neurobiologist and author Ari Berkowitz, thinks this search is misguided because human brains are so varied.


According to Berkowitz, many people assume human brain sex differences are innate, but this assumption is misguided.


Humans learn quickly in childhood and continue learning – alas, more slowly – as adults. From remembering facts or conversations to improving musical or athletic skills, learning alters connections between nerve cells called synapses. These changes are numerous and frequent but typically microscopic – less than one hundredth of the width of a human hair.


Some London taxi drivers do not use GPS – they know the city by heart, a learning process that takes three to four years on average.


Studies of an unusual profession, however, show learning can change adult brains dramatically. London taxi drivers are required to memorize “the Knowledge” – the complex routes, roads and landmarks of their city. Researchers discovered this learning physically altered a driver’s hippocampus, a brain region critical for navigation. London taxi drivers’ posterior hippocampi were found to be larger than nondrivers by millimeters – more than 1,000 times the size of synapses.


So it’s not realistic to assume any human brain sex differences are innate. They may also result from learning. People live in a fundamentally gendered culture, in which parenting, education, expectations and opportunities differ based on sex, from birth through adulthood, which inevitably changes the brain.


Ultimately, any sex differences in brain structures are most likely due to a complex and interacting combination of genes, hormones and learning.


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