The showing in regard to age substantiates the observation already made that our modern immigration is in no sense an immigration of families. This, too, affects the chances for assimilation very considerably. As regards the economic efficiency of the immigrants, the age distribution, added to the sex distribution, marks them as a selected group. When it is further considered that the physically and mentally feeble, and those who are unlikely to be able to earn their own living are weeded out in the process of inspection, it appears that those who look upon the immigrant as nothing more than a source of cheap labor have much reason to be pleased with the quality of our immigration. The productive power of a group of immigrants averages very much higher than a corresponding number of persons taken from the general population of the race from which they come. Herein lies perhaps the greatest and most popular argument for immigration. It is claimed that without our foreign laboring force it would have been impossible to develop the resources of the country so rapidly and completely as they have been developed, and that if the supply were cut off now, it would seriously cripple the entire industry of the country. It is certainly true that under the present organization of industry in this country, production in many lines depends to a very important degree upon foreign labor. How much of truth there is in the deduction that without the immigrants this country would be much farther back in the industrial race than it is to-day, will be considered in another connection.[160] There are many citizens of the United States, however, who look upon the immigrant as something more than a mere productive machine. To them the proof of his economic efficiency is not sufficient. They wish to know something of his adaptability to assimilation into the American life, and of his probable contribution to the ethnic type of the United States. To such as these, there are a number of further conditions which must be considered, and which are of at least equal significance in determining the final effects of immigration upon this country. Prominent among these is the intellectual quality of the immigrant. This is naturally a very difficult thing to measure. Beyond actual feeble-mindedness, the only test of intellectual capacity which has received wide application is the literacy—or, as it is more frequently expressed, the illiteracy—test. This concerns the ability to read and write, and is given a great deal of weight by many students of the subject. It is not, however, necessarily an indication of intellectual capacity, but rather of education. The inability to read or write may be due to lack of early opportunity, rather than to inferior mental caliber. Nevertheless, the matter of literacy has received sufficient attention, and is in fact of sufficient importance, so that it is desirable to have the facts in this respect before us.