Author Robert Wright argues that history has an arrow: That humans have continued to evolve -- if not biologically, than culturally and technologically -- toward greater complexity and intelligence. He also explains the concept behind his book, "Nonzero": That life is a nonzero sum game, where there can be more than one winner, and that civilization evolved thanks to such endeavors, which reward cooperation, rather than competition. His guarded optimism is tinged with a deep worry over the growing prevalence of grass-roots hatred. His hope: that the intelligent pursuit of self-interest will actually be the world's salvation. Robert Wright is author of The Moral Animal and NonZero. He also hosts an excellent interview series called meaningoflife.tv.