While Charles Darwin's vision of evolution was brilliant, natural selection ignores a crucial force that helps to explain the diversity and wonder of life: symbiosis. In Darwin's Blind Spot, Frank Ryan shows how the blending of life forms through symbiosis has resulted in gigantic leaps in evolution. The dependence of many flowering plants on insects and birds for pollination is an important instance of symbiosis. More surprising may be the fact that our cells have incorporated bacteria that allow us to breathe oxygen. And the equivalent of symbiosis within a species -- cooperation -- has been a vital, although largely ignored, force in human evolution. In Ryan's view, cooperation, not competition, lies at the heart of human society. Ryan mixes stories of the many strange and beautiful results of symbiosis with accounts of the dramatic historic rivalries over the expansion of Darwin's theory. He also examines controversial research being done today, including studies suggesting that symbiosis among viruses led to the evolution of mammals and thus of humans. Too often Darwin's interpreters have put excessive emphasis on competition and struggle as the only forces in evolution. But the idea of "survival of the fittest" does not always reign. Symbiosis is critically important to the richness of Earth's life forms.