Cooperation is the means by which life arose in the first place, but given what we know about the mechanisms of evolution, it is also something of a puzzle. How does cooperation begin, when on a Darwinian level, all that the genes in your body care about is being passed on to the next generation? A biologist by training, Nichola Raihani looks at where and how collaborative behavior—teaching, helping, grooming, and self-sacrifice—emerges throughout the animal kingdom, and glimpse the traits that have made humans so distinctive and so successful.