Modernity tried to whitewash our tribal selves, to erase the vestiges of the savannah in our genome. But like graffiti in a city, our inner caveman is irrepressible. The ancient hominid self springs up unpredictably and in unexpected places. The tribe underlies the most fundamental parts of our identities, but that doesn’t mean it’s easy to pin down. How far have we moved from our small bands of foragers? Digital technologies like social networking sites and cell phones return us to an age of tribal-style social immersion.