The recognition of this truth was one of the outstanding contributions of Herbert Spencer to the science of sociology. Whereas other writers had stressed the power of the environment, as a purely material thing, in shaping human institutions, Spencer placed chief stress upon the emotional and intellectual life of primitive man as determining their beginnings. He showed how man's feelings and beliefs about himself, and about his fellows, and about the world of living forces with which he believed himself to be surrounded, were the all-important factors of social evolution. And the subsequent history of society has been such that scientific sociology is very largely the study of the growth and elaboration of an essentially psychical environment. The lower animal world--except so far as we allow for the operation of instincts--has, broadly, only the existence of other animals and the physical surroundings for its environment. With man it is vastly different. Owing primarily to language, the environment of the man of to-day is made up in part of the ideas of men who lived and died thousands of years ago. The use of clothing and the invention of tools would alone make mind a dominant fact in human life. But apart from these things, the great fact of social heredity, in virtue of which one generation enjoys the acquired culture of preceding generations, and without which civilisation would have no existence, is a great and dominant _mental_ fact. Our institutions, our customs, are transmitted to us as so many psychic facts. Every new invention, every fresh culture acquisition, is helping to strengthen and broaden the psychical environment of man. Each newcomer is born into it; it moulds his nature and determines his life, as his own career and his own acquisition help to mould the life of his successors. Whether the phenomena be simple or complex, whether we are dealing with man in a civilised or in an uncivilised state, there is no escape from the general truth that man is everywhere under the domination of his mental life.