§ 11. #Magnitude of the inflow of immigrants.#In view of these facts it seems necessary to modify the displacement theory greatly. To the extent that the coming of immigrants caused a net addition to the population, it doubtless hastened the growth of cities and the development of industrialism, and thus helped to reduce the birthrate in some classes. But this view admits the effect upon population which the displacement theory denies. Probably, in a good many cases the more rapid business advancement of the natives, because of the coming of the immigrants, led to the decline of birthrate that is a consequence of economic success.[9] But a large part of this change would have inevitably occurred even if there had been no immigration after 1820. Between 1820 and 1910 the population increased 82,400,000, and the total number of immigrants was 27,800,000, or 33.7 per cent of the total increase. In an urban environment the birthrate among immigrants always has been very much higher than that of native Americans. This fact alone might well be taken as sufficient to offset whatever depressing effects the coming of the immigrants may have had upon the native birthrate, leaving the immigration nearly a net addition to population. It does not seem possible to believe that if there had been no immigration, our native population, rapidly advancing in average wealth, wages, and general education, would have continued with an unchecked birthrate, and would have filled all the places taken by immigrants. And no believer in the displacement theory has ever ventured to claim, as the argument requires, that if immigration were now stopped, the birthrate would again return to the old standard of 1820, or would cease to decrease somewhat. Especially of late, since the rate of increase of the native population has become much less, is the effect of continuing immigration apparent. In the decade of 1900-1910 the total population increased 16,000,000, while nearly 9,000,000 immigrants arrived. Of the remaining increase, 3,000,000 consisted of children born of foreign parents. That leaves three or at the most four million (4,000,000) increase attributable to the native stock, white and negro combined.