That this is no overstatement of the issue, a bare recital of a few biological axioms will show. We have already seen that nothing is more _unstable_ than the racial make-up of a people, while, conversely, nothing is more _unchanging_ than the racial divisions of mankind. We have seen that true amalgamation is possible only between members of the same race-stock, while in crossings between stocks even as relatively near together as the main divisions of the white species, the race-characters do not really fuse but remain distinct in the mixed offspring and tend constantly to resort themselves as pure types by Mendelian inheritance. Thus a country inhabited by a mixed population is really inhabited by different races, one of which always tends to dominate and breed the other out--the outbred strains being lost to the world forever. Now, since the various human stocks differ widely in genetic worth, nothing should be more carefully studied than the relative values of the different strains in a population, and nothing should be more rigidly scrutinized than new strains seeking to add themselves to a population, because such new strains may hold simply incalculable potentialities for good or for evil. The potential reproductive powers of any stock are almost unlimited. Therefore the introduction of even a small group of prolific and adaptable but racially undesirable aliens may result in their subsequent prodigious multiplication, thereby either replacing better native stocks or degrading these by the injection of inferior blood. The admission of aliens should, indeed, be regarded just as solemnly as the begetting of children, for the racial effect is essentially the same. There is no more damning indictment of our lopsided, materialistic civilization than the way in which, throughout the nineteenth century, immigration was almost universally regarded, not from the racial, but from the material point of view, the immigrant being viewed not as a creator of race-values but as a mere vocal tool for the production of material wealth. Immigration is thus, from the racial standpoint, a form of procreation, and like the more immediate form of procreation it may be either the greatest blessing or the greatest curse. Human history is largely the story of migrations, making now for good and now for ill. Migration peopled Europe with superior white stocks displacing ape-like aborigines, and settled North America with Nordics instead of nomad redskins. But migration also bastardized the Roman world with Levantine mongrels, drowned the West Indies under a black tide, and is filling our own land with the sweepings of the European east and south. Migration, like other natural movements, is of itself a blind force. It is man's divine privilege as well as duty, having been vouchsafed knowledge of the laws of life, to direct these blind forces, rejecting the bad and selecting the good for the evolution of higher and nobler destinies.