Evolutionary psychologists regard psychopathy as an inherited personality style that has evolved because glib, deceitful individuals—as a minority within a larger population of trusting folk—often reproduce with much success.So in other words, psychopaths are Hawks in the Chicken game of life. What’s nice about this explanation is that it not only explains why psychopaths exist, but also why we’re not all psychopaths. If there are few enough psychopaths in the population, then being a psychopath makes sense because you’ll mostly have winning confrontations with nice people. But if there are too many psychopaths, then the gains from taking advantage of nice people will be swamped by the losses from confronting other psychopaths. In equilibrium, you’ll get both psychos and nice folks, with each strategy generating approximately equal returns, and with the precise balance determined by the relative payoffs of different interactions.
With that explanation on the table, I found this one less plausible: “Other investigators ... regard psychopathy as the result of a still-unspecified genetic disorder. The inherited defect interferes with the workings of the brain's emotion system, which is centered in the amygdala, a structure especially concerned with perceiving dangerous situations.” Possible; but if psychopathy is a genetic defect, you have to wonder why it hasn’t been more completely weeded out of the population. Genetic defects can persist, of course, but usually because they produced some kind of balancing benefit in some evolutionary environment – e.g., the heterozygous form of sickle-cell anemia provides some protection against malaria. So when I see an alleged “defect,” I always look for the adaptive explanation.