"But in a community of many races, there is either cross-breeding or there is not. If there is, the children of such cross-breeding are liable to inherit two souls, two temperaments, two sets of opinions, with the result in many cases that they are unable to think or act strongly and consistently in any direction. The classic examples are Cuba, Mexico, and Brazil. On the other hand, if there is no cross-breeding, the diversity exists in the original races, and in a community full of diverse ideals of all kinds much of the energy of the higher type of man is dissipated in two ways. First, in the intellectual field there is much more doubt about everything, and he tends to weigh, discuss, and agitate many more subjects, in order to arrive at a conclusion amid the opposing views. Second, in practical affairs, much time and strength have to be devoted to keeping things going along old lines, which could have been spent in new research and development. In how many of our large cities to-day are men of the highest type spending their whole time fighting, often in vain, to maintain standards of honesty, decency, and order, and in trying to compose the various ethnic elements, who should be free to build new structures upon the old! "The moral seems to be this: Eugenics among individuals is encouraging the propagation of the fit, and limiting or preventing the multiplication of the unfit. World-eugenics is doing precisely the same thing as to races considered as wholes. Immigration restriction is a species of segregation on a large scale, by which inferior stocks can be prevented from both diluting and supplanting good stocks. Just as we isolate bacterial invasions, and starve out the bacteria by limiting the area and amount of their food-supply, so we can compel an inferior race to remain in its native habitat, where its own multiplication in a limited area will, as with all organisms, eventually limit its numbers and therefore its influence. On the other hand, the superior races, more self-limiting than the others, with the benefits of more space and nourishment will tend to still higher levels. "This result is not merely a selfish benefit to the higher races, but a good to the world as a whole. The object is to produce the greatest number of those fittest not 'for survival' merely, but fittest for all purposes. The lower types among men progress, so far as their racial inheritance allows them to, chiefly by imitation and emulation. The presence of the highest development and the highest institutions among any race is a distinct benefit to all the others. It is a gift of _psychological environment_ to any one capable of appreciation."[152]