A number of scientists argue that we have a so-called ‘behavioral immune system’ that functions to protect us against strangers who might carry germs against which we have no immunity. (Discover)
I have long believed that tribalism is inborn, but I had focused mostly on the cognitive limits of reciprocity and trust. This is another, intriguing, idea.
Science discovers link between patriotism and evil,
http://www.sciencedaily.com/releases/2009/06/090625115237.htm
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