This very fact is sometimes used as an excuse for the whole procedure. It is claimed that the natives are not displaced, but are simply forced into higher occupations. Those who were formerly common laborers are now in positions of authority. While this argument holds true of individuals, its fallacy when applied to groups is obvious. There are not nearly enough places of authority to receive those who are forced out from below. The introduction of five hundred Slav laborers into a community may make a demand for a dozen or a score of Americans in higher positions, but hardly for five hundred. Furthermore, in so far as this process does actually take place, it must result in a lowering of the native birth rate, for it is a well-known fact that in all modern societies the higher the social class, the smaller is the average family. What has been said thus far refers to the limitation of families after marriage. The same influences work to produce the same result in another way. The increased difficulty in earning enough to support a family, due to immigration, leads countless American young men to postpone marriage for many years, and perhaps an equal number to give up marrying altogether. Both result in a great decrease in the birth rate for society as a whole.[189] The processes sketched above are mainly volitional. There is a variety of other influences, which work unconsciously, but perhaps none the less powerfully, to accomplish the same result. General Walker asserted that the shock produced on the American mind by the miserable class of immigrants in the thirties and forties, in itself, had a profoundly detrimental effect on the natural rate of reproduction. Immigration has the effect of vastly increasing congestion of population, and congestion limits its growth. Furthermore, in an average group of immigrants, the males exceed the females by more than two to one.[190] The introduction of such an unnatural element into the population must limit its reproductive power.