Men's and women's brains are different. Found this on boingboing.net, a directory of wonderful things. Indeed! Here is more from the scientists explaining this fascinating photo:

Gray matter represents information processing centers in the brain, and white matter represents the networking of – or connections between – these processing centers. This, according to Rex Jung, a UNM neuropsychologist and co-author of the study, may help to explain why men tend to excel in tasks requiring more local processing (like mathematics), while women tend to excel at integrating and assimilating information from distributed gray-matter regions in the brain, such as required for language facility. These two very different neurological pathways and activity centers, however, result in equivalent overall performance on broad measures of cognitive ability, such as those found on intelligence tests.Link