Sec. 10. #The displacement theory; its fundamental assumption.# The latter opinion which still has many upholders[6] was first advanced by a distinguished economist, Francis A. Walker, but his first statement of it referred only to the period between 1830 and 1860.  The main argument in support of this opinion was that in the three decades from 1830 to 1860 during which a large immigration occurred, the decennial rates of increase of the population were almost the same as in the three decades from 1800 to 1830.[7] The conclusion drawn from these figures is that the immigrants were the cause of the decline of the average birthrate that occurred in the families of native stock.  The validity of this conclusion is absolutely dependent on the assumption that no other forces were at work to produce this result.  Must we believe that, but for immigration, the native birthrate would not have declined at all?  This is incredible.  The birthrate of the native stock had already begun to decline before 1820 as is shown by many family records, and by the fall of the decennial rate of increase from 35 and 36 in the decades ending 1800 and 1810, to 33.1 and 33.5 in the next two decades.  This occurred despite the enormous western settlement then under way on the Louisiana Purchase.  The decline of the birthrate began at that time to appear as a world-wide phenomenon, accompanying improved transportation (roads, steamboats, steam railways), the rapid growth of cities, and the general industrial revolution.  The general birthrate has declined of recent years in Australia and New Zealand, where there has been little immigration, more rapidly than it has in the United States.[8]

Sec. 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