What do colon cancer, ant colonies, language and global warming have in common? This might sound like the front end of a joke, but in fact it’s a serious challenge to the standard view of evolution. Martin A. Nowak, the director of the Program for Evolutionary Dynamics at Harvard, has devoted a brilliant career to showing that Darwin, and particularly his followers, batted only two for three. Random mutation and natural selection have indeed been powerful motors for change in the natural world — the struggle for existence pitting the fit against the fitter in a hullabaloo of rivalry. But most of the great innovations of life on earth, Nowak argues, from genes to cells to societies, have been due to a third motor, and “master architect,” of evolution: cooperation.