 James argues that the central key to Darwin’s natural selection mechanism is to decouple the causes of variation from the causes of selection (see Lewens, 2007, Ch. 2). Variations are produced by unknown causes, and the environment selects among them. Variations themselves (for James’s Darwin) are inexplicable. The same is true of great men: ‘The causes of production of great men lie in a sphere wholly inaccessible to the social philosopher. He must simply accept geniuses as data, just as Darwin accepts his spontaneous variations’ (James, 1880, 445). Great men, like spontaneous variations, are essential and inexplicable elements of the evolutionary process. Just as Darwin’s theory credits environment and variation with distinctive, yet vital, roles, so both great men and the social environment are important for the explanation of social change: