Scientists have quibbled for years over who cheats more: Men or women? Research from paleoanthropologist Dean Falk, of the State University of New York at Albany, indicates that men might, and it may be related to the size of their brains. Until now, it had been generally accepted that the sexes had the same size brain once their proportions were taken into account. But after meticulously plotting human brain-size statistics onto a curve, Falk discovered that men's brains, on average, are four ounces larger than those of women. Falk suspects the size discrepancy can be linked to the philandering tendencies of our primate ancestors.Falk found that like humans, male rhesus monkeys had larger brains than females, while male and female gibbon apes were equally endowed. Rhesus males, however, leave the family group at adulthood and search for multiple mates, while gibbons are monogamous. Falk reasoned that the extra neurons of men and rhesus males are most likely dedicated to visual-spatial skills, such as map reading, distinguishing between left and right, and mentally rotating figures--all abilities useful for navigating uncharted territories in search of mates. And Falk thinks it's no accident that men consistently outperform women on tests of those skills. "We think the male brain has more hardware to handle the graphics, like a souped-up computer," Falk says. "But I knew right away that it couldn't be because men are more intelligent than women."