In the early twentieth century, varied audiences took biology out of the hands of specialists and transformed it into mass culture, transforming our understanding of heredity in the process. In the early twentieth century communities made creative use of the new theories of heredity in circulation at the time, including the now largely forgotten mutation theory of Hugo de Vries. Science fiction writers, socialists, feminists, and utopians are among those who seized on the amazing possibilities of rapid and potentially controllable evolution. De Vries's highly respected scientific theory only briefly captured the attention of the scientific community, but its many fans appropriated it for their own wildly imaginative ends. Writers from H.G. Wells and Edith Wharton to Charlotte Perkins Gilman, J.B.S. Haldane, and Aldous Huxley created a new kind of imaginary future, which Jim Endersby calls the biotopia. It took the ambiguous possibilities of biology--utopian and dystopian--and reimagined them in ways that still influence the public's understanding of the life sciences. The Arrival of the Fittest recovers the fascinating, long-forgotten origins of ideas that have informed works of fiction from Brave New World to the X-Men movies, all while reflecting on the lessons--positive and negative--that this period might offer us.