and finally the sociology, followed during the next twenty years; and the synthesis of the world-process which these volumes lucidly and persuasively developed, probably did more than any other work, at least in England, both to drive home the significance of the doctrine of evolution and to raise the doctrine of Progress to the rank of a commonplace truth in popular estimation, an axiom to which political rhetoric might effectively appeal.

Many of those who were allured by Spencer’s gigantic synthesis hardly realised that his theory of social evolution, of the gradual psychical improvement of the race, depends upon the validity of the assumption that parents transmit to their children faculties and aptitudes which they have themselves acquired.  On this question experts notoriously differ.  Some day it will probably be definitely decided, and perhaps in Spencer’s favour.  But the theory of continuous psychical improvement by a process of nature encounters an obvious difficulty, which did not escape some critics of Spencer, in the prominent fact of history that every great civilisation of the past progressed to a point at which instead of advancing further it stood still and declined, to become the prey of younger societies, or, if it survived, to stagnate.  Arrest, decadence, stagnation has been the rule.  It is not easy to reconcile this phenomenon with the theory of mental improvement.

The receptive attitude of the public towards such a philosophy as Spencer’s had been made possible by Darwin’s discoveries, which were reinforced by the growing science of palaeontology and the accumulating material evidence of the great antiquity of man.  By the simultaneous advances of geology and biology man’s perspective in time was revolutionised, just as the Copernican astronomy had revolutionised his perspective in space.  Many thoughtful and many thoughtless people were ready to discern—­as Huxley suggested—­in man’s “long progress through the past, a reasonable ground of faith in his attainment of a nobler future.” and Winwood Reade, a young African traveller, exhibited it in a vivid book as a long-drawn-out martyrdom.  But he was a disciple of Spencer, and his hopes for the future were as bright as his picture of the past was dark.  The martyrdom of man, published in 1872, was so widely read that it reached an eighth edition twelve years later, and may be counted as one of the agencies which popularised Spencer’s optimism.

That optimism was not endorsed by all the contemporary leaders of thought.  Lotze had asserted emphatically in 1864 that “human nature will not change,” and afterwards he saw no reason to alter his conviction.