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. 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. In the 20th and 21st centuries, researchers looked for distinctively female or male characteristics in smaller brain subdivisions. As a behavioral neurobiologist and author , I think this search is misguided because human brains are so varied.
The largest and most consistent brain sex difference has been found in the hypothalamus, a small structure that regulates reproductive physiology and behavior.
At least one hypothalamic subdivision is larger in male rodents and humans. But the goal for many researchers was to identify brain causes of supposed sex differences in thinking β not just reproductive physiology β and so attention turned to the large human cerebrum, which is responsible for intelligence.
Within the cerebrum, no region has received more attention in both race and sex difference research than the corpus callosum, a thick band of nerve fibers that carries signals between the two cerebral hemispheres.
