It is reasoning in a circle to assert that man evolved from lower creatures because of natural selection in a struggle for existence, and then use this fact as proof of the overpopulation which caused the process. Nevertheless, there is not the least doubt that science has conclusively established the fact of the evolution, which could not have occurred unless there had been overpopulation. It is not possible to understand the present evolution of man, and his past migrations, without a very clear conception of his origin, for past and present history are based on the same conditions.
There is no doubt that man's ancestor resembled, in a general way, the present anthropoids or man-like creatures. At some remote period, it so happened that by a change to a glacial climate or some other equally effective cause, it was so much more difficult to find food and to escape his enemies and other adverse conditions, that only the most intelligent survived in each generation, the least intelligent being ruthlessly destroyed by starvation or other means. The next generation inherited the larger brain of the survivors and the size of the brain must have been increased very rapidly from generation to generation. In the course of some thousands of years the process developed a creature sufficiently intelligent to be called man. The old theory that man increased his own brain by exercising it, had to be given up as it had no facts to support it and was like lifting one's self by the boot straps. It was once taught that he civilized himself without brains to do it, and then grew brains from being civilized. Now we know that civilization did not arise until long after man evolved sufficient brain - evolved by natural selection for the purpose of survival. The civilization of all races is directly proportional to their average brain development, for each does its best with the brains at hand. During the evolution of man the mortality of the fools was dreadful. Civilization is a fool saver. There is no proof, indeed it can be definitely disproved, that exercise of the brain increases the numbers of elements or cells. These proofs do not concern us here, but the reader interested in the matter can find them in an article by the writer on "The Evolution of the Small Brain of Civilized Man," in the American Journal of Insanity July, 1901.
Not only does migration to a milder environment check further increase of brain, but so does civilization also by itself. In the latter case, the more stupid are not killed off, because every one can make a living somehow and the result is an increasing variation. At the present time, therefore, we have as variations from the average, larger and better brains than ever existed before. The average has not increased - probably has decreased owing to the survival of so many of the stupid smaller brained people.
In savage life the average brain is the best for survival because all men must do the same things. Hence, wide variations perish and there is a wonderful similarity in the skulls. If a higher race forces civilization on a lower, as the Spanish did upon the Malay, variations survive and uniformity ceases. Gustave Le Bon showed the increasing variations of modern skulls - a generalization based upon the measurements of some thousands* Consequently, we now have better specialists than ever existed, all cooperating in the division of labor or the orchestration of civilization, and we also have a large number of smaller brains of useful type than existed among our savage ancestors.
* Recherches anatomiques et mathematiques sur les variations de volume des cerveaux et leurs relations avec l'intelligence. Paris, 1879.