Decades before the American Revolution, Benjamin Franklin lamented that English settlers were constantly fleeing over to the Indians-but Indians almost never did the same. Tribal society has been exerting an almost gravitational pull on Westerners for hundreds of years, and the reason lies deep in our evolutionary past as a communal species. The most recent example of that attraction is combat veterans who come home to find themselves missing the incredibly intimate bonds of platoon life. The loss of closeness that comes at the end of deployment may explain the high rates of post-traumatic stress disorder suffered by military veterans today.