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(H)e (Darwin) supposed that man, before he even emerged from apedom, was already a social being, living in small scattered communities. Evolution in his eyes was carried out mainly as a struggle between communities - team against team, tribe against tribe. Inside each team or tribe, the 'ethical cosmos' [the dual code of Amity and Enmity] was at work, forging and strengthening the social bonds which made the members of such a team a co-operative whole. … Thus, in the early stages of human evolution we find competition and co-operation as constituent elements of the evolutionary process …

Co-operation and unity give strength to a team or tribe; but why did neighboring tribes refuse so stubbornly to amalgamate? If united, they would have got rid of competition and struggle. Why do human tribes instinctively repel every thought of amalgamation, and prize above all things independence, the control of their destiny, their sovereignty? Here we have to look beneath the surface of things and formulate a theory to explain tribal behavior. How does a tribe fulfill an evolutionary purpose? A tribe is a 'corporate body,' which Nature has entrusted with an assortment of human seed or genes, the assortment differing in some degree from that entrusted to every other tribe. If the genes are to work out their evolutionary effects, then it is necessary that the tribe or corporation should maintain its integrity through an infinity of generations. If a tribe loses its integrity by a slackening of social bonds, or by disintegration of the parental instincts, or by lack of courage or of skill to defend itself from the aggression of neighboring tribes, or by free interbreeding with neighbors and thus scattering its genes, then that tribe as an evolutionary venture has come to an untimely end. For evolutionary purposes it has proved a failure.

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Tribalism was Nature's method in bringing about the evolution of man. I have already explained what a tribe really is - a corporation of human beings entrusted with a certain capital of genes. The business of such a corporation is to nurse and develop its stock of genes - to bring them to an evolutionary fruition. To reach such an end a tribal corporation had to comply with two conditions: (1) it had to endure for a long age; (2) it had to remain intact and separate from all neighboring and competing tribes. Human nature was fashioned or evolved just to secure these two conditions - continuity through time and separation in space. Hence the duality of man's nature - the good, social, or virtuous traits serving intratribal economy; the evil, vicious, or antisocial qualities serving the intertribal economy and the policy of keeping its genes apart. Human nature is the basal part of the machinery used for the evolution of man. When you know the history of our basal mentality - one fitted for tribal life - do you wonder at the disorder and turmoil which now afflict the detribalized part of the world?”