Intellectual or moral divergence produced by these two primary causes would tend to determine the course of social evolution along different lines and so to produce different types of social organisation. And different social organisations thus produced would then react upon the moral and intellectual life of the people to produce further divergence; for example, one type of social organisation determined by physical environment, say a well developed patriarchal system, may have made for progress of intellect and morals; another, say a matriarchal organisation, or one based on communal marriage, may have tended to produce stagnation. As social evolution proceeded and brought about more extensive and more complex forms of social organisation, which included, within any one society or group, larger numbers of individuals in more effective forms of association, social organisation must have assumed a constantly increasing importance as a condition of mental evolution relatively to all other factors, especially as compared with the influence of physical environment; until, in the complex societies of the present time, it has an altogether predominant importance. This truth is concisely stated in the old dictum that “in the infancy of nations men shape the State; in their maturity the State shapes the men.” Accordingly, in considering the mental evolution of peoples we must never lose sight of the influence of social organisation. It follows that the conditions of the mental evolution of man are immensely more complex than those of the mental evolution of animals.