itself in our religions, rules of conduct, in our laws, in our customs."[150] The vital necessity of restriction and selection in immigration to conserve and build race-values is thus set forth by Mr. Hall: "There is one aspect of immigration restriction in the various countries which does not often receive much attention; namely, the possibility of its use as a method of world-eugenics. Most persons think of migration in terms of space--as the moving of a certain number of people from one part of the earth's surface to another. Whereas the much more important aspect of it is that of a functioning in time. "This comes from two facts. The first is that the vacuum left in any country by emigration is rapidly filled up through a rise in the birth-rate.... The second fact is that immigration to any country of a given stratum of population tends to sterilize all strata of higher social and economic levels already in that country. So true is this that nearly all students of the matter are agreed that the United States would have a larger population to-day if there had been no immigration since 1820, and, it is needless to add, a much more homogeneous population. As long as the people of any community are relatively homogeneous, what differences of wealth and social position there may be do not affect the birth-rate, or do so only after a considerable time. But put into that community a number of immigrants, inferior mentally, socially, and economically, and the natives are unwilling to have their children associate with them in work or social life. They then limit the number of their children in order to give them the capital or education to enter occupations in which they will not be brought into contact with the new arrivals. This result is quite apparent in New England, where successive waves of immigration from lower and lower levels have been coming in for eighty years. In the West, the same New England stock has a much higher birth-rate, showing that its fertility is in no way diminished. In the South, where until very recently there was no immigration at all, and the only socially inferior race was clearly separated by the accident of color, the birth-rate has remained very high, and the very large families of the colonial period are even now not uncommon.