organic rank, but also because most of the varying environments within any one civilization are not absolutely imposed upon the individual, as are experiments upon the lower organisms. This is not meant to imply that differences between one historical age and another, or any other imposed environment from which there is no escape, may not be found of considerable importance in relation to certain sociological and historical facts. For instance, the total number of eminent men in western Europe probably increases too rapidly from the fourteenth century to the sixteenth not to be in part due to the force of circumstances.[1] Also I have statistics in the course of compilation which indicate that there is evidence that women are advancing in noteworthiness of achievement in the United States with each elapsed decade. These imposed and unescapable conditions, which change with the course of history and affect entire races or great groups of people, must be clearly distinguished from the class of environments that exist within any one age and in any one state of civilization.
There are doubtless other ways in which man and other mammals are directly modified by their environment in an essential and lasting way, but to enter into a discussion of these questions is useless in connection with this generalization. Such are the modifications produced by poisons, diseases of a bacterial or other nature, which the individual accidentally encounters. The necessary knowledge has not yet been gained for any generalization, from a comparative point of view, in regard to these complicated processes, so that we should be able to say that these changed conditions affect higher organisms more than lower Moreover, the same poison may be for one kind of protoplasm a great change and for another a slight one, and we have already seen that the proportionate amount of change in the outward conditions is necessarily of prime importance in determining the end result.
These chemical questions do not fall within the literature contained in text-books of experimental zoology, which, to review and rearrange has been the chief purpose of this article. The entire analogy of such experiments, as well as the results of special studies on the relative influence of heredity and environment, can lead to but one conclusion, and that is, that the value of modification diminishes as evolution proceeds.
I know that to generalize is dangerous and exceptions may be found which seem to conflict with the laws or principles which are here set forth, but often apparent exceptions find explanation in the light of further knowledge. I put these laws forth with some hesitancy, yet feel that enough is known to take a step beyond hypotheses and trust that the future will confirm their essential truth.
