Head size correlates statistically with intelligence, a not-widely known fact - greater cranial volumes are linked to higher intelligence. The correlation, while small, has been reported in multiple studies. And because, on average, men's bodies are bigger than women's, their heads too are larger than women's. So, one might reasonably expect men to be more intelligent than women. This is not the case, however - men and women consistently score equally on intelligence tests. For neuroscientists, this paradox has long presented a puzzle. If head size correlates with intelligence, and women have smaller heads, why don't they have lower intelligence?
Researchers at the University of Pennsylvania Medical Center now report new findings that may help explain the conundrum: Women have a higher proportion of gray matter to cranial volume than men. Conversely, men have higher proportions of white matter and cerebrospinal fluid to cranial volume than women. Gray matter refers to the neuronal cell bodies and their dendrites, the short protrusions that communicate with immediately neighboring neurons in the brain. White matter refers to the longer axons, sheathed in a white fat called myelin, that reach out from neurons to more distant regions of the brain. Cerebrospinal fluid is the liquid in which the brain floats inside the head. Gray matter is where computation takes place, while white matter is responsible for communication between groups of cells in different areas of the brain.
"With these findings, we are beginning to get an explanation for the
lack of intelligence disparity between men and women," says Ruben C. Gur, Ph.D.,
professor of psychology in psychiatry and lead author on the new study, which
will appear in the May 15 issue of the Journal of Neuroscience. "Women have a
higher percentage of tissue devoted to computation than men. Men have a greater
proportion of tissue assigned to the transfer of information between distant
Contact: Franklin Hoke
University of Pennsylvania School of Medicine