We still think tribally. Team sports? Mostly small bands competing with other small bands, replaying competitions for prized territory. We do mock battles for fun.

Our ancestral hominids emerged as hunter-gatherers in competition with each other and other animal life. The biological imprint of that lifestyle still colors our behavior. We remained hunter-gatherers for over 200,000 years and it wasn’t urban living.

Population densities remained low until farming at scale began 10,000 years ago; the earliest cities formed soon afterward. We are fast adapting to crowded living, but old behavioral patterns persist.

The tribal boundaries we draw are familiar, based on geography, skin color, language, religion, self-identity, profession and — most powerfully — economic interests. These fluid boundaries can intersect and overlap, dissolve, merge and split, through manipulation, cooperation and force.

It’s amazing that we have functional (as distinct from sustainable) cities of 20+ million people. World population today is 54% urban. We are getting better at getting along. Our tribal tendencies are one part of our troubles, but they’re not the bug.

In the deep past, in those small hunter-gatherer groups of mostly family living in a world where hominids are not apex predators, being cast out from your tribe was a death sentence. That was the daily reality. This creates a powerful — arguably instinctual — incentive to stay on good terms with the tribe. It’s still a fundamental driver for human behavior today.

How much of what we do is guided by social convention? We are born immersed in our local culture; it strongly influences our behavior and thinking. We recognize other cultures think and act differently, but we remain focused on our own local customs.

Historically, when your tribe says you must believe something to remain in the tribe, then your own survival and self-preservation requires you to get with the program. That was literally true during the hunter-gatherer stage and remains socially true now. Our musical tastes, language, films, dances, art, all vary between cultures and generations and serve as unifiers, social glue. That’s a positive, right? A feature, not a bug?

Here’s the bug. If you have to deny reality to get along, most people will.

This is why the Emperor’s New Clothes story resonates. We see it happen in fads, in financial swings, rumors, churches.

Social fictions can unify populations and aid problem-solving. They can also divide and magnify problems. Whatever the value set is, when beliefs rooted in social fictions clash with reality, people feel tribal unity is threatened and react accordingly. This intense impulse runs deep.

These contractions of trust polarize by tribe. That warning you feel in your gut regarding current events is real; it’s conditioned by hundreds of thousands of years of tribal living…and warfare.

Let us not underestimate just how malleable people can be. Start with a large group who aren’t the brightest and not conspicuously successful, or a group that lacks access to good education, or has longtime simmering resentments due to suppression by race, religion, geography, etc.

Salt such groups with people who tell them they’re patriotic heroes and their tribe is endangered. Give them weapons and point them to another group. Tell them the fate of the tribe is in their hands.

They’ll do their best. Happens all the time.

Is there a way out? It’s hard to be certain in unique conditions. Given the pressure of climate change, we’d do better do it soon. Humanity could make a good start by discarding social fictions and update our understanding of who we really are. Then can we begin aligning sustainable values with reality.

Edit 2–4–18: Andrew Sullivan gets it. When Two Tribes Go to War