"As neuroimaging research has exploded over the past quarter century, it has become evident that males and females show certain group-level differences in brain structure. Adult male brains are some 14% larger than female brains, with bigger ventricles, a higher ratio of white:gray matter, and a longer period of growth during adolescence (e.g., Lenroot et al., 2007). These differences are reliable enough that most brain morphometry studies now use sex as a covariate when analyzing mixed-sex samples."