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.Biologist E. O. Wilson on Why Humans, Like Ants, Need a Tribe
And so it has ever been. In ancient history and prehistory, tribes gave visceral comfort and pride from familiar fellowship, and a way to defend the group enthusiastically against rival groups. It gave people a name in addition to their own and social meaning in a chaotic world. It made the environment less disorienting and dangerous. Human nature has not changed. Modern groups are psychologically equivalent to the tribes of ancient history. As such, these groups are directly descended from the bands of primitive humans and prehumans.
The drive to join is deeply ingrained, a result of a complicated evolution that has led our species to a condition that biologists call eusociality. “Eu-,” of course, is a prefix meaning pleasant or good: euphony is something that sounds wonderful; eugenics is the attempt to improve the gene pool. And the eusocial group contains multiple generations whose members perform altruistic acts, sometimes against their own personal interests, to benefit their group. Eusociality is an outgrowth of a new way of understanding evolution, which blends traditionally popular individual selection (based on individuals competing against each other) with group selection (based on competition among groups). Individual selection tends to favor selfish behavior. Group selection favors altruistic behavior and is responsible for the origin of the most advanced level of social behavior, that attained by ants, bees, termites—and humans.