The Blank Slate: The Modern Denial of Human Nature

by Steven Pinker

The genetic economics of sex also predicts that both sexes have a genetic incentive to commit adultery, though for partly different reasons. A philandering man can have additional offspring by impregnating women other than his wife. A philandering woman can have better offspring by conceiving a child by a man with better genes than her husband while having her husband around to help nurture the child. But when a wife gets the best of both worlds from her affair, the husband gets the worst of both worlds, because he is investing in another man’s genes that have usurped the place of his own. We thus get the flip side of the evolution of fatherly feelings: the evolution of male sexual jealousy, designed to prevent his wife from having another man’s child. Women’s jealousy is tilted more toward preventing the alienation of a man’s affections, a sign of his willingness to invest in another woman’s children at the expense of her own.