I recently came across a very interesting piece in the NY Post which cites a study that shows that while it was well known that a difference in size between male and female brains exists, there is now evidence that there are significant differences in the size of certain structural parts of the brain, according to gender.
As such, researchers have found, for instance, that a female’s frontal lobe, responsible for problem-solving, is larger than in a man. Meanwhile, a male’s amygdala, which regulates sexual behavior and “fight or flight” reaction, is bigger.
Surprisingly, for me at least, it seems in male brains, men have six and a half times more gray matter than women do. Gray matter is partly responsible for information processing, so may explain in general men tend to be better in math.
As for women, it seems human females have 10 times as much white matter -- the part of the brain that's I partially responsible for connecting information processing centers. This could contribute to the stereotype that why women are good multi-taskers.
Of course, this doesn't prove anything. This doesn't mean men are smarter than women, just because their brains are bigger, or that women will always be more detail orientated than men and so on. Quality is not proven by size, like in most aspects of life. Hormones, genetic different and more add to the puzzle that compose the human brain, be it man or woman, but this particular research remains very interesting, still.
You can read the hypothesis in greater detail here. I'd love to hear some thoughts on this very controversial piece.