Assuming no freak hospital mix-ups, mothers can be 100% sure that a child that she bears and raises is, in fact, genetically her own. Fathers, however, can’t be quite so sure. Even if “dad” engages in vigilant mate guarding, there’s always the possibility that his partner snuck off for some horizontal mambo action with another guy. Evolutionary psychologists call this the “paternal certainty problem”— men who have been cuckolded and are unknowingly raising a child that’s not their own have failed, from an evolutionary perspective, at passing on their genes. And it turns out that a significant number of men have failed to solve this problem.