The first was that we were so tuned to sort the world into “us” and “them” that we would do so based on the lightest of cues. The second was that once we had sorted the world into “us” and “them,” we would act with favor toward our group and discriminate against the out-group—even in the absence of any reason to do so. Atop this theory, Tajfel conducted a series of famous experiments that would be farcical were the results not so chilling.
