From The New York Times:
These days gender inequality is commonly explained by neurological differences, most popularly the notion that the surge of testosterone that occurs in the eighth week of fetal development affects the relative size of the right and left hemispheres of the brain, and of the corpus callosum, the bundle of neurons that connects the two. In the 1980s Norman Geschwind proposed that the surge results in a smaller left hemisphere for males, leaving them with greater potential for right-hemisphere development, which, as he put it, results in “superior right-hemisphere talents, such as artistic, musical, or mathematical talent.” In female brains the hemispheres are more collaborative, explaining women’s superior verbalizing skills.
There are two problems here, Dr. Fine says. First is that several studies have found no difference in hemispheric size in neonates. The supposedly larger female corpus callosum is also in dispute. But even if size difference does exist (as it does in rats), she says, “getting from brain to behavior has proved a challenge.” Given that there may be sex differences in the brain, “what do they actually mean for differences in the mind?” Dr. Baron-Cohen builds on this theory, suggesting that low levels of testosterone result in a female, “E type” brain (for empathy); medium levels yield a balanced brain; and high levels a male, “S type” brain (for systemizing). Medium levels account for the fact that some girls are systemizers and some boys are empathizers.