History traces the evolution of the social structure in which the community exists to-day. There are three chief factors at work in this evolution; racial descent, culture drift, and transmission of language: the first of these physiological and not necessarily connected with the other two, whilst those two are not always associated with each other. In the evolution of the social structure the factor of first importance is the transmission of culture, which is not a matter of heredity but due to contact, for culture is learned and reproduced by imitation and not inherited. Culture must be taken in the widest sense to include political, social, and legal institutions, the arts and crafts, religion, and the various forms of intellectual life which show their presence in literature, philosophy, and otherwise, all more or less connected, and all having the common characteristic that they cannot be passed on by physical descent but must be learned in after life. But race, culture, and language resemble one another in so far as it is true that all are multiplex and perpetually interwoven, so that in each the lines of transmission seem rather like a tangled skein than an ordered pattern; results proceed from a conflicting group of causes amongst which it is often difficult to apportion the relative influences.