William Flesch in the Los Angeles Review of Books:
Some evolutionary biologists, David Sloan Wilson among them, think that there are reasons for seeing human cooperation as deriving from a genuine genetic propensity for altruism. Altruism and prosocial tendencies may be taken as roughly synonymous. Species (humans pre-eminently) that tend to engage in behavior which promotes the general welfare — even at the cost of some individual sacrifice — are able to cooperate in ways that help everyone.
They can do this despite the huge risk that free riders will derail the whole system. What prevents free riders from undermining altruism by taking such advantage of altruists that they die out? The answer that many evolutionary biologists, evolutionary psychologists, sociologists, anthropologists, neuroscientists, game theorists, and, even narrative theorists like yours truly, have converged on is the concept of what’s now known as altruistic punishment.
The idea behind altruistic punishment is that uninvolved third party witnesses will punish defectors, cheaters, and free riders. They, or a significant number of them, won’t let a self-dealer or serious violator of social norms get away with social or moral transgressions, even if they have to pay a price themselves. And they won’t even let those who are indifferent to the violators get away with such transgressions either. Many people are still angry at the 38 people who allegedly witnessed the rape and murder of Kitty Genovese from the safety of their apartments in 1964 and didn’t bother to call the police.