Prejudice is terrible, but is it uniquely human? No, according to a new research on rhesus macaques by Yale psychologist Laurie Santos. Blame evolution:

"One of the more troubling aspects of human nature is that we evaluate people differently depending on whether they're a member of our 'ingroup' or 'outgroup,'" Santos said. "Pretty much every conflict in human history has involved people making distinctions on the basis of who is a member of their own race, religion, social class, and so on. The question we were interested in is: Where do these types of group distinctions come from?"

The answer, she adds, is that such biases have apparently been shaped by 25 million years of evolution and not just by human culture.

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