Mr. Whelpley says, “There is no hope of an exhaustion of supply, for the most prolific races are now contributing their millions, and yet increasing the population of their own countries. There is no hope of an improvement in quality, for the best come first and the dregs follow.”[373] Professor Mayo-Smith says, “Emigration does not threaten to depopulate the countries of Europe. Had there been no emigration during this century (the nineteenth) it is not probable that the population of Europe would have been any greater than it is. The probabilities are all the other way.”[374] Professor Taussig, while not stating this opinion in so many words, appears to adhere to it when he says that without emigration Sweden and Italy would have had—not a larger population—but either a higher death rate or a lower birth rate.[375] If we seek for a statistical demonstration of the foregoing argument we are confronted with the same impossibility of securing it which has become so familiar in the course of this work. These matters do not adjust themselves with clocklike regularity, but operate over long periods, and are complicated by innumerable other factors. Even though two phenomena are shown to operate harmoniously, it is not always possible to prove which is cause and which effect. The declining birth rate has been a common phenomenon in almost all European countries during the last forty years, and particularly during the last twenty years of the nineteenth century.[376] An opponent of the view we are considering could point to this fact as a contradiction of the claim, while one on the opposite side could assert that the decline would have been equally rapid and perhaps more so without any emigration at all. Neither could prove his case. Even if it could be demonstrated that the countries which experience the largest emigration also manifest the highest rate of increase in population, it might be easily maintained that it was the extreme growth of population that accounted for the large emigration, rather than the reverse. About all that can be shown is that a large emigration and a high rate of increase of population may go together. Examples of this state of affairs are numerous.[377]