CUMULATIVE EVIDENCE FOR EVOLUTION 



change and those of biologic change the closest parallelism. 

 Whenever the rocks tell us a story of relatively sudden con- 

 tinental uplift, with its associated climatic changes and 

 stormy times, we find a corresponding adaptive change in 

 the organisms preserved in the rocks. Whether the organ- 

 isms 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 cer- 

 tainly 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 that 



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