Jack London lived (1876-1916) at a time when a dramatically new set of ideas, growing out of the theory of evolution, was changing the course of men’s thinking. These ideas stimulated, frustrated, and tantalized London all his adult years. Charles Darwin and Herbert Spencer, messiahs of the new creed, became his intellectual mentors, along with Friedrich Nietzsche and Karl Marx. It might be said that London’s very real private struggle with life — which he dramatized in stories so arresting and exciting that they are still read over the world — became for him an epitome of the Darwinian Struggle for Existence,...