Have you ever wondered why, in the ongoing presidential campaign, we so strongly hear the pipes calling us to arms? Why the religious among us bristle at any challenge to the creation story they believe? Or even why team sports evoke such intense loyalty, joy, and despair?

The answer is that everyone, no exception, must have a tribe, an alliance with which to jockey for power and territory, to demonize the enemy, to organize rallies and raise flags.