Old As Sin

"What made this result even more remarkable" noted Neha Mahajan, a Yale graduate student who headed up this project, "is that monkeys in this population move around from group to group, so some of the monkeys who were 'outgroup' were previously 'ingroup.' And yet, the result holds just as strongly for monkeys who have transferred groups only weeks earlier, suggesting that these monkeys are sensitive to who is currently to be thought of as an insider or an outsider. In other words, although monkeys divide the world into 'us' versus 'them,' they do so in a way that is flexible and is updated in real time."
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The researchers then recorded the time monkeys spent looking at both kinds of sequences. The monkeys spent little time looking at sequences that included ingroup faces paired with good stuff like fruits or outgroup faces paired with bad stuff like spiders, suggesting that the monkeys treated these two kinds of stimuli as being similar. On the other hand, the monkeys stared longer at sequences in which outgroup individuals were paired with positive objects like fruit suggesting that this association was unnatural to the monkeys. Like humans, monkeys tend to spontaneously view ingroup members positively and outgroup members negatively.
The Yale team's results suggest that the distinctions humans make between "us" and "them" -- and therefore the roots of human prejudice -- may date back at least 25 million years, when humans and rhesus macaques shared a common ancestor. (Via.)