Here I would revert to some points of the analogy, drawn in Chapter X, between the mind of a nation and that of an individual. The mind of an individual human being develops by accumulating the results of his experience; and so does that of a people. In this respect the analogy holds good. But the development possible to an individual is strictly limited in two ways. First, by the short duration of the material basis of his mental life; secondly by the extent of his innate capacities. Neither of these limitations applies to the national mind. Its material basis is in principle immortal, because its individual components may be incessantly renewed; and its development has no limit set to it by its innate capacities, because these may be indefinitely extended and improved. In these respects the national mind resembles the species rather than the individual. The development of the national mind, and of the minds of those who share in the mental life of the nation, thus combines the methods and advantages of the development of individuals and of species, methods which are essentially different. The result is that the mental development of man, since his social life began, has been radically different from that of the animals; it has been a social process; it has been the evolution of peoples rather than of individuals. The evolution of man as an individual has been wholly subordinated to that of peoples; and it is incapable of being understood or profitably considered apart from the development of the group mind. Assuming, as we must, that all the races of men are derived from a common stock, it is obvious, I think, that the first differentiation of racial types was determined almost exclusively by differences of physical environment, and that the other conditions only very slowly developed and did not assume their predominant importance until the time which may be roughly defined as the beginning of the historic or nation-making period. Physical environment affects the mental qualities of a people in three ways: firstly, it directly influences the minds of each generation; secondly, it moulds the mental constitution by natural selection, adapting the race to itself; thirdly, it exerts indirect influence by determining the occupations and modes of life and, through these, the social organisation of a people. We may consider these three modes of influence in turn. There has been much speculation on the direct influence of the physical environment in moulding the mental type of a people, but little or nothing can be said to be established.