not necessarily follow that quantitative differences do not connote qualitative differences as well. On the contrary, not only among the phenomena of physical science, but also throughout the whole realm of the biological world, quantitative differences do have a commonly recognized qualitative significance. One indicates the presence of the other, but does not in the remotest manner explain it. A single quantitative difference, moreover, is sufficient to give rise to a set of qualitative changes of so marked a character as to constitute a wholly new species. The consequent changes which may possibly result, and which would seem to be out of all proportion to the initial change, occur according to the well known law in biology of correlative variation. Organs and functions so hang together that a seemingly insignificant quantitative change in one part often carries with it a marked transformation of the entire organism itself. It is simply begging the question to argue, for instance, that inasmuch as the human brain closely resembles the brain of the higher order of the anthropoid apes and as the only discernible difference is chiefly that of volume, or rather extent of effective surface, therefore the differences between the ape and man may be reduced at the last analysis to the quantitative one of brain dimensions. The very point at issue is not this obvious difference which is expressible in quantitative terms, but the question whether this difference of bulk is sufficient to account for the qualitative differences which are correlated with it, namely,—conceptual thinking, speech, the use of tools, the dominance over the animal world and the control of nature, a moral sense and religious aspiration, the faculty to look before and after, to learn from the past and to plan for the future.
It will be urged that animals show all of these seemingly characteristic features of man, though in a less degree. It is indeed true that animals do show the rudiments of all these so-called higher qualities of man. The significant point of it all is that they remain in the rudimentary stage generation after generation. And there is no evidence of any progress leading beyond what seems to be a final and complete stage of development. Man shows, however, a unique capacity of exhibiting in forms of increasing progression the limitless possibilities of the evolution process. In him all natural forces become tremendously acceler-
