Now it is quite obvious that the earth cannot hold, and cover with water, a mass of oyster shells eight times as great as itself; the oceans, if they were spread evenly over the surface (which they never were, and never can be), would accommodate but a few of the great horde. Neither do those same oceans contain enough food to satisfy, or begin to satisfy, the needs of these theoretical descendants of a single oyster. Clearly, therefore, space and food alone are enough to prevent the undue multiplication of creatures upon the earth. But there are factors other than space and food which aid in accomplishing the result. There are water conditions, animal enemies such as the starfish, and a host of other means by which the population of oysters is kept down. And even if it were to increase greatly, the numbers of starfish would at the same time increase, and simultaneously set about decreasing the numbers of the oysters, which decrease would in turn cut down the numbers of the starfish, and so on. Thus we see that the maximum abundance of an organism is arbitrarily set by the conditions under which that organism lives. It may attain the limit set for it, but beyond that it may go only temporarily. Then the surplus dies from starvation, crowding, animal and plant enemies, and a thousand other of the factors which constantly work in the constant warfare of nature, the never-ending “struggle for existence.” The third factor of Darwinian evolution, that of natural selection, is based upon the other two. Darwin supposed that the individuals of a species, or variety, exhibited variations for two reasons: because it was part of their very nature to do so, and because the conditions of their environment forced them. In the course of this constant change there would, of necessity, be some modifications that were of value to their possessors, while others would appear which were of more or less definite harm. In the course of the struggle for existence, those creatures which possessed helpful variations would naturally possess a certain advantage over those which lacked it or which exhibited variations which were of harmful nature. Thus in a cold, snowy climate, that animal which developed a white coat would be much safer from detection than his companions which might have fur of a dark hue, either in approaching his prey, or in escaping his pursuers. The ultimate outcome of this would be that the white animal would populate the region, while his colored brethren would soon become extinct. The same principle, Darwin thought, applied to mental advantages; the more skillful mind triumphed over the less; the quick-witted animal lived at the expense of the clumsy-witted one. Throughout the earth, those animals most capable of living lived, brought forth young, and thus perpetuated their capabilities, both mental and physical. This process quite plainly helped in the development of man, and in his progress, but singularly enough,