This remarkable comparison between the rapidity of actual progress and the extreme slowness of the biological development resulting from the survival of the fittest in the Darwinian struggle for existence, will be enough to show anybody that progress is not one movement but two; and whilst the survival of {95} the fittest explains the slow and almost imperceptible movement, the rapid and perceptible movement is explained by the leadership of the greatest. It is with the rapid movement alone that the practical sociologist is concerned; and hence for him the great man, not the fittest, is the important factor. Let us now consider what is meant by the process called social evolution, regarded as something distinct from those intentional advances made and maintained by the genius of great men. To understand this, we must consider what is meant by evolution generally. Mr. Spencer defines it in terms of “_the homogenous_” and “_the heterogenous_”; and from his own point of view we may accept his definition as correct. But facts have many aspects; and according to the purpose with which we deal with them they will require different definitions, which, though none of them are incompatible with the others, will have between themselves no apparent resemblance. Thus the biologist’s definition of a man will be quite distinct from the theologian’s; and the dangerous illness of a great party leader will be one phenomenon for his followers, and quite another for his doctor. In the same way Mr. Spencer’s definition of evolution, however admirable it may be from a certain point of view, is not exhaustive. It entirely leaves out of sight those characteristics of the process which it is necessary before all things that the practical sociologist should understand.