It has been written that 'Male brains have about 6.5 times more gray matter' and 'Female brains have about 10 times more white matter.', so I looked up the original study. Turns out those numbers correspond to the number of voxels (pixels in a structural MRI) whose gray matter or white matter volumes correlates significantly with performance in an IQ test, not to the amount of matter. So what this says is that men's gray matter's size is variable in more areas than women's when comparing different IQs, and the converse for white. It says nothing about the overall amount of gray matter or white matter in males vs. females. The mistake was made by Molly Edmonds' summary of Bjorn Carey's summary of the results, not by the authors of the study.