CUMULATIVE EVIDENCE FOR EVOLUTION
change and those of biologic change the closest parallelism. Whenever the rocks tell us a story of sudden continental uplift, with its associated climatic changes and stormy times, we find a corresponding adaptive change in the organisms preserved in the rocks. Whether the organisms respond directly to the changes in environment, or whether there is merely a change in standards of survival and an elimination of the less adaptable forms, we do not certainly know. Nothing could be clearer, however, than that there is a causal relation between organic and inorganic rhythms. Thus once more the unity of the whole process is impressed upon our minds. Organic evolution must be viewed not as an isolated process, but as an integral part of a vast system of orderly change.
No one line of evidence of organic evolution can possibly be conclusive in itself, though to the expert in each field his own data seem to need no outside support. The real proof of the validity of the concept of evolution lies in the fact that all lines of evidence point in exactly the same direction and are fully consistent with and corroborative of one another. Not only is this so, but each kind of evidence throws light upon all the other kinds. The obscure spots in one field are illuminated by facts derived from other fields. Thus the proof of organic evolution is cumulative. Before Charles Darwin recorded the results of his epoch-making work the known facts supporting the theory of evolution were few and unorganized. It is to the everlasting credit of Darwin that he amassed and organized so large and conclusive a body of evidence of evolution that he practically established the validity of the theory single handed.
The real test of the value of a theory, however, is not that it explains and rationalizes only the particular body of data it was devised to explain. It would be a poor theory
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