In the past, I’ve commented on my belief that people’s tendency to group together in social units and eagerly defend their compatriots while damning their foes probably goes back to our tens of thousands of years evolving in tribal groups. In this blog post about political division, I wrote…

The general view from the left seems to be that you can’t just disagree with conservatives, you must hate them with every fiber of your being, and the inverse is true from the right. People go to great lengths to segregate themselves from people who don’t think like they do.
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[This] might make some sense from an evolutionary perspective. When we existed in small tribes, the rest of the world really was out to destroy you, so it was pretty easy to assign the worst motivations to the “them” in “us and them.”

The biologist E.O. Wilson has a new book out exploring this very concept. This article of his summarizes parts of it. One interesting point: once people have joined their group (whether it be fans of certain sports team, people with like-minded politics or people with the same skin color) they’re willing to believe the worst about others.

Experiments conducted over many years by social psychologists have revealed how swiftly and decisively people divide into groups and then discriminate in favor of the one to which they belong. Even when the experimenters created the groups arbitrarily (italics mine), prejudice quickly established itself. Whether groups played for pennies or were divided by their preference for some abstract painter over another, the participants always ranked the out-group below the in-group. They judged their “opponents” to be less likable, less fair, less trustworthy, less competent. The prejudices asserted themselves even when the subjects were told the in-groups and out-groups had been chosen arbitrarily.

I think we’ve all felt this, especially as teenagers. You get arbitrarily assigned to some group (maybe “people whose last name starts with the same first letter is yours”) and you feel a certain bonding for your fellow members and a certain derision for members of all their groups. (“Those people whose last name begins with ‘P’… they’re scum.”) Soon you’re casting taunts at these “others,” then throwing rocks at them. Then you are raiding their villages, killing their men, raping their women, and heartlessly slaying their children before them.

Come on, admit it, we’ve all done it.