At first glance this may seem almost a self-evident proposition. That it is not, however, is evidenced by the strikingly large number of the deeper thinkers on the subject who hold the opposite view. Of these, the best known in this connection is General Francis A. Walker. In his discussion of this problem he says: “Space would not serve for a full statistical demonstration of the proposition that immigration, during the period from 1830 to 1860 instead of constituting a net reënforcement to the population, simply resulted in a replacement of native by foreign elements; but I believe it would be practicable to prove this to the satisfaction of every fair-minded man.”[180] Mr. Prescott F. Hall, who quotes this passage, holds firmly to the same opinion himself, and cites a number of other writers who are more or less positive in their statements of the causal relation between immigration and the diminishing native birth rate. Mr. F. A. Bushee, whose authority on matters of population is well recognized, says, “The multiplication of foreign peoples has seriously checked the growth of the old American stock.”[181] Mr. Robert Hunter is a pronounced advocate of this view, and says, “The immigrants are not additional inhabitants. Their coming displaces the native stock.”[182] Professor John R. Commons supports this position throughout his discussions of the subject. An extreme but convincing opinion is that expressed by Mr. S. G. Fisher in the _Popular Science Monthly_ for December, 1895. After a careful statistical survey of the growth of population in the United States he states his conviction that “immigration has not materially increased, but, on the contrary, has somewhat decreased the American population.... All the immigrants and all their increase cannot make up for the loss of the old rate of increase of the natives.” In view of this imposing weight of authoritative opinion, it is perhaps surprising that the popular mind still holds so tenaciously and universally to the belief that immigration directly increases population. The explanation probably lies in ignorance of the facts of the case and of the fundamental laws of population and in the somewhat abstruse nature of the reasoning by which the expert conclusions are reached. For it must be admitted frankly that this is not a proposition which can be demonstrated in an absolutely conclusive mathematical way, which will leave no further ground for argument. The factors affecting population are many and complicated, including not only immigration, but war, vice, hard times, marriage customs, the growth of cities, and a host of other things. It is far beyond the present power of social science to define positively the relative importance of each of the forces involved in producing a certain phenomenon.