Human prejudice may date back 25 million years or more, scientists say

“One of the more trou bling as pects of hu man na ture is that we eval u ate peo ple dif fer ently de pend ing on wheth er they’re a mem ber of our ‘in group’ or ‘out­group,’” San tos said. “Pretty much eve ry con flict in hu man his to ry has in volved peo ple mak ing dis tinc tions on the ba sis of who is a mem ber of their own race, re li gion, so cial class, and so on. The ques tion we were in ter est ed in is: Where do these types of group dis tinc tions come from?”

The an swer, she adds, is that such bi ases have ap par ently been shaped by 25 mil­lion years of ev o lu tion and not just by hu man cul ture.

“The bad news is that the ten den cy to dis like out group mem bers ap pears to be ev o lu­tion arily quite old, and there fore may be less sim ple to elim i nate than we’d like to think,” San tos said. “The good news, though, is that even mon keys seem to be flex i ble about who counts as a group mem ber. If we hu mans can find ways to har ness this evolved flex i bil ity, it might al low us to be come an even more tol er ant species.”

San tos and mem bers of her lab stud ied rhe sus ma caque mon keys liv ing on an is land off the coast of Puerto Rico. Mon keys in this popula t ion nat u rally form dif fer ent so cial groups based on family his to ry.