For the purposes of research phenomena must be isolated, but the investigator must not be betrayed into imagining that this isolation ever occurs under actual conditions. Every "change" is an "event," but it is not on that account to be regarded as an "accident." To the individual ignorant of the conception of natural process, everything must appear "accidental"; to the scientist, however, "accident" is natural process out of focus for a particular investigator at a given time. So, while "the system of nature is certainly in rule," it admits of changes taking place, and "change in one part of the universe involves a change throughout. No part lives unto itself, but all are members one of another."
It is apparent, then, that there are two ways by which the study of an evolution may. be approached—we may begin with the isolation and description either of the processes manifested in "change," or of those manifested in "fixity." In adopting the first course, the assumption of "uniformity" requires the further assumption, made by Lyell and Darwin, of unlimited time for the operation of "gradual modifications"; in adopting the second, we must follow the historical record in order to observe the actual course of change. In the first instance, evolution is thought of as a flowing stream of change continuously moving forward in a direction from lowest to highest; in the second, it is conceived as a series of experiments in adjustment or adaptation,[1]broken in upon, from time to time, by conflicting experiments of the same sort. The mode of thought induced by the first approach tends to a forgetfulness of the essential fact that in nature no process appears in isolation ; the point of view of the second demands a constant vigilance in regard to changes occurring outside the field immediately under investigation.
It must not be thought that this alternative mode of approaching the study of evolution is brought forward as a contribution
- ↑ C. B. Davenport, Congress of Arts and Science, St. Louis, 1904 (Boston, 1906), V, 250, says: "Only within the last few years have we come to recognize that every organ is more than a homologue: it is also a successful experiment with the environment."
