He projected a vast 10-volume work, Synthetic Philosophy, in which all phenomena are interpreted according to the principle of evolutionary progress. Together with Charles Darwin and Thomas Huxley he was responsible for the acceptance of the theory of evolution.
Although no longer influential in biology, his extension of his theory of evolution to psychology and sociology remains important. His "Social Darwinism" was particularly influential on early evolutionary economists such as Thorstein Veblen.
The Study of Sociology is Spencer's popular account of his leading sociological doctrines. Its publication marked the emergence of Spencer as the popular philosopher of the Victorian age. It was a highly influential work in terms of the impetus it gave to the academic pursuit of the new science of sociology and it also played an important role in shaping the outlook of many thoughtful lay persons in the Victorian reading public.
The Study of Sociology is used not only as a textbook at Yale, but was the textbook used for the first course in Sociology in the United States. Sociology became a discipline in the United States because of Spencer's impressive work.
