For millions of years, humans have been seeking out tribes, be they religious, ethnic, economic, political, or even musical (think of the Deadheads). It’s our nature. Now the Internet has eliminated the barriers of geography, cost, and time. All those blogs and social networking sites are helping existing tribes get bigger. But more important, they’re enabling countless new tribes to be born — groups of ten or ten thousand or ten million who care about their iPhones, or a political campaign, or a new way to fight global warming. And so the key question: Who is going to lead us?