Small isolated communities are the cradles in which new tribal breeds of
mankind are reared. But how do new races arise? If isolation were to be
continued throughout long intervals of time we may justly infer that the
physical and mental characters of a breed would become more and more
emphasized until a stage of differentiation is reached which we must
regard as racial. A racial spirit is merely the tribal spirit matured
and consolidated. The manifestations which begin as tribal, end, in the
course of time, by becoming racial. We cannot account for the
differentiation of mankind into distinct races, nor the existence of
many intermediate forms which link one human race to another, unless we
postulate the existence in mankind of a deeply rooted tribal mechanism.