From Jonathan Haidt (made known to me by a friend’s Facebook post):

Despite what you might have learned in Economics 101, people aren’t always strictly selfish. In politics, they’re more often groupish. When people feel that a group they value — be it racial, religious, regional or ideological — is under attack, they rally to its defense, even at some cost to themselves. We evolved to be tribal, and politics is a competition among coalitions of tribes.

The key to understanding tribal behavior is not money; it’s sacredness. The great trick that humans developed at some point in the last few hundred thousand years is the ability to circle around a tree, rock, ancestor, flag, book or god, and then treat that thing as sacred.

People who worship the same idol can trust one another, work as a team and prevail over less cohesive groups. So if you want to understand politics, and especially our divisive culture wars, you must follow the sacredness.