‘Evolution’ is very generally looked upon as the central idea of modern scientific and philosophical thought. ‘Democracy’ is for many the final goal, or at least it is the inevitable path, of our political and social progress. It is reasonable to connect the two terms and to ask ourselves what light can be thrown by biological conceptions upon the theoretical and practical problems of society. But we must guard carefully against the rhetorical and un-critical use of phrases which have a scientific sound, or which have served as the watchwords of eager struggles. Those who believe themselves advanced thinkers are sometimes apt to treat everything that takes place through evolution as if it were identical with progress, and to take it for granted that the democratic movements of our age must, simply because they are the movements of our age, be all of them of a progressive kind. More cautious thinking suggests many difficulties; and it is sometimes even argued that biology throws no light whatever upon sociology, theoretical or practical. In the enthusiasm caused by the theories of Mr Herbert Spencer and the discoveries of Darwin it was often too lightly assumed that society could be explained by the direct application of the formulae which had proved so successful in the biological sphere. ‘The social organism’ seemed to be a key to unlock political and social mysteries. The structure and the functions of society were thought to be fully intelligible only if approached from the biological side.