Noting that, for all the challenges of modern life, humanity is better off right now than it has ever been, Glenn Reynolds suggests that some of our more-persistent hangups might derive from long years of slow evolution:

Our brains are still wired, in large part, for caveman times: A time when the stock of wealth was largely fixed (hunter-gatherers couldn’t create more antelopes, or more berries), so that if one person had more, that inevitably meant that another had less, and when strangers — meaning, basically, the people over the next hill — had every reason to try to take it away from you. These two caveman attitudes produce the zeal for redistribution that is now marketed as socialism and the tribalism that is still a major part of politics.

We don’t live in the caveman era now. Wealth isn’t fixed, but the product of human ingenuity — cavemen couldn’t make more antelopes, but we can invent gadgets and services that never existed before. And in free markets, we entrust our lives to strangers not of our tribe every time we fly in an airplane, drive on the highway or check in to a hotel.

From this point of view, insisting on dividing people into tribes so that the finite yield of the hunt can be distributed is the thinking of troglodytes.  Sounds about right.