The tribal or clannish spirit tends to manifest itself in many forms,
but in all its varieties there is a common factor--that of isolation. At
first sight we are tempted to regard the tribal spirit as part of a
machinery evolved for the protection and survival of a primitive
community, but to any one who has searched for conditions which will
explain the origin of separate races of mankind, the conviction grows
that the tribal spirit is an essential part of Nature's evolutionary
machinery. It was in these isolated cradles of primitive mankind that
Nature nursed and reared new races. When a breeder wishes to produce a
new type of animal, or to preserve a 'sport', his first step is to
isolate the group of animals with which he is to experiment. The
isolated stock becomes the cradle in which he hopes to rear his new
breed. The experimental breeder, in such instances, copies the
conditions which rule in primitive human communities. Under modern
civilization Nature's cradles have been smashed to atoms, but the tribal
instincts which Nature intended for the propagation of new breeds of
humanity have come down to modern man in undiminished force. Hence our
present national and racial troubles.