“When we see beings as belonging to a particular group, for instance, we start to believe there's something fundamental and biological that unites all the creatures in that group, that there's some invisible essence that makes a dog a dog and a cat a cat. We do the same thing with humans: if we are told that a category is important, we infer that the people in the people in that category share a fundamental essence. We essentially them. And the more a category is emphasized, the more we think its members have a unifying thread.”