Because their genes would want them to. Paradoxically, a male (for instance, man) who invests highly in his kids is more likely to stray than someone (say a male chimp) who invests very little. Evolutionary psychologists argue that even if loving and caring is their main goal, bang-bang-bye-mam makes for a good genetic gamble, provided the father keeps looking after his lawful child. But while females in other species have no chance of getting more from another male—one male chimp is as good as another—the human female does, and a failure to get it from any male can be quite costly. So, while nature may favour men adept at deceiving women, it may also favour women who can see through them. Indeed, males who often depict themselves as more kind, sincere, and trustworthy than they actually are, may be indulging in self-deception. Explains Robert Wright in The Moral Animal: "That means to feel deep affection for a woman who, after a few months of sex, may grow markedly less adorable."
