When we survey a country still in the most primitive stage of human society, the first observation to impress us is the fact that its inhabitants are separated into definitely isolated groups. Such groups are usually small, consisting of men, women, and children belonging to several closely related families and numbering two or three hundred souls. Each group, forming an elemental community, occupies, and considers itself the owner of, a definite tract of country; there is developed in them a feeling--an attachment--which serves to bind them to the soil on which they live. When we look at the nature of the bonds which serve to bind the members of a primitive community together, we see that they are formed out of subconscious impulses or instincts. These instincts form an essential part of the machinery of organization. There is usually no head man or chieftain to determine the action of the community; there is no deliberative assembly to lay down rules of conduct. In Galton's phrase the members of a primitive community form 'a sentient web', dominated by traditional beliefs and customs. I have no wish to analyse the subconscious states and instinctive reactions which rule and bind together the members of a primitive community; what I want to make clear is that the tribal instincts have above all an isolating effect. These instincts serve not only as a machinery for binding the members of a community together, but also as a means of separating them from all surrounding groups. Within the community this machinery compels unity of sentiment and of action; it serves to repress schism and faction. But the tribal machinery is operative only up to the territorial boundaries of the community. At that limit the tribal instincts immediately change in their mode of action. The tribal instincts surround the community with a frontier, across which there is no peaceful traffic, only robbery and plunder; or at the best covert enmity. The tribal frontier is also a blood barrier; across it the tribal instinct forbids any form of peaceful matrimonial exchange or tribal intermixture. Nothing impressed Darwin so much as the ring of neutral territory which surrounded the primitive Fuegian settlements. TRIBAL ISOLATION PROVIDES THE CONDITIONS NECESSARY FOR RACE-BREEDING