This Is Your Brain, On Sex

Does size matter to Larry Summers and/or his critics?

Scientists working at Johns Hopkins University, recently reporting in the "Cerebral Cortex" scholarly journal (1), have discovered that there is a brain region in the cortex, called inferior-parietal lobule (IPL) which is significantly larger in men than in women. This area is bilateral and is located just above the level of the ears (parietal cortex).

Furthermore, the left side IPL is larger in men than the right side. In women, this asymmetry is reversed, although the difference between left and right sides is not so large as in men, noted the JHU researchers. This is the same area which was shown to be larger in the brain of Albert Einstein, as well as in other physicists and mathematicians. So, it seems that IPL's size correlates highly with mental mathematical abilities.

Not to worry gals:

Another previous study by the same group led by Dr. Godfrey Pearlson (9) has shown that two areas in the frontal and temporal lobes related to language (the areas of Broca and Wernicke, named after their discoverers) were significantly larger in women, thus providing a biological reason for women's notorious superiority in language-associated thoughts. Using magnetic resonance imaging, the scientists measured gray matter volumes in several cortical regions in 17 women and 43 men. Women had 23% (in Broca's area, in the dorsolateral prefrontal cortex) and 13% (in Wernicke's area, in the superior temporal cortex) more volume than men.

These results were later corroborated by another research group from the School of Communication Disorders, University of Sydney, Australia, which was able to prove these anatomical differences in the areas of Wernicke and of Broca (3). The volume of the Wernicke's area was 18% larger in females compared with males, and the cortical volume the Broca's area in females was 20% larger than in males.

And the reason for the above differences:

According to the Society for Neuroscience, ... "In ancient times, each sex had a very defined role that helped ensure the survival of the species. Cave men hunted. Cave women gathered food near the home and cared for the children. Brain areas may have been sharpened to enable each sex to carry out their jobs". Prof. David Geary, at the University of Missouri, USA, a researcher in the area of gender differences, thinks that "in evolutionary terms, developing superior navigation skills may have enabled men to become better suited to the role of hunter, while the development by females of a preference for landmarks may have enabled them to fulfill the task of gathering food closer to home." (2) The advantage of women regarding verbal skills also make evolutionary sense. While men have the bodily strength to compete with other men, women use language to gain social advantage, such as by argumentation and persuasion, says Geary.

....During the development of the embryo in the womb, circulating hormones have a very important role in the sexual differentiation of the brain. The presence of androgens in early life produces a "male" brain. In contrast, the female brain is thought to develop via a hormonal default mechanism, in the absence of androgen. However, recent findings have shows that ovarian hormones also play a significant role in sexual differentiation.

One of the most convincing evidences for the role of hormones, has been shown by studying girls who were exposed to high levels of testosterone because their pregnant mothers had congenital adrenal hyperplasia (4). These girls seem to have better spatial awareness than other girls and are more likely to show turbulent and aggressive behaviour as kids, very similar to boys'.

The ball is now in the Reality Based Community's court.