ABSTRACT
The human race is only one of the millions of species of animals that the earth has brought forth ; many of which were in existence long before man appeared. For countless millenniums after his appearance his numbers were few as compared with those of other species, but during the last two centuries human population has increased manyfold in Europe and America, and there are now portions of these countries more densely populated by man than it ever was by any other of the larger animals. However, his total of less than two billion individuals can be duplicated in numbers by the lower forms of life found in any small pond, or in a few rods of soil.
