Yesterday, PLoS One published a study entitled “The Rationality of Prejudices” by Thomas Chadefaux and Dirk Helbing, which argues that being prejudiced can be an efficient strategy:
We model an -player repeated prisoner’s dilemma in which players are given traits (e.g., height, age, wealth) which, we assume, affect their behavior. The relationship between traits and behavior is unknown to other players. We then analyze the performance of “prejudiced” strategies. . .Such prejudiced strategies have the advantage of learning rapidly. . .they perform remarkably well. . .when the population changes rapidly.
The key assumption is right there in the abstract:
We model an -player repeated prisoner’s dilemma in which players are given traits (e.g., height, age, wealth) which, we assume, affect their behavior. (emphasis added)
In short, the researchers are starting with the assumption that the prejudices are true. So, being prejudiced can be a good strategy, if the prejudices are true and not very many individuals are prejudiced. What they have really shown is that, in a Prisoner’s Dilemma game, players can learn to be prejudiced quickly enough for the prejudiced strategy to be efficient, assuming, again, that the prejudice actually reflects reality.
Research into reputation has clearly shown that prior knowledge about the likelihood that another individual will cooperate does make cooperation more likely. This study assumes that this reputation can be inferred from readily observable characteristics.
Assuming that physical characteristics (e.g., height, color, age) are significantly correlated with behavior is reasonable as a theoretical exercise, but requires evidence of its existence if this is to be treated as an explanation of real and abhorrent human behavior. Absent that evidence, efforts to wave away the ethical implications of this argument seem naive at best.
If you know that you are from a group in which most individuals are willing to cooperate with other members of the group, then identifying group members by readily observable characteristics would be useful. It seems more likely to me that prejudices are a mis-application of this local in-group identification to broader scales that have not been relevant for the vast majority of mammalian social evolution. Abhorrent practices like prejudices in our modern society do not necessarily require an explanation that shows their continued adaptiveness, but may be harmful relics of an evolutionary past when social dynamics were much more local and the perils of day-to-day life were so extreme that “ethics” was an unaffordable luxury.