58 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



of organic evolution. The basis of the accepted theory of geological 

 evolution is the " uniformitarian doctrine" of Lyell, which assumes 

 that the key to the past lies in the present, that the changes that are 

 going on today are of the same order and kind as those of the past, 

 and, finally, that there is neither beginning nor end to the earth's 

 evolutionary history, but that a slow and orderly development has 

 gone on and will continue indefinitely. The proof of this conception 

 consists of an array of facts derived from a study of the earth's crust, 

 including its stratified structure, of traces of animal and plant life 

 preserved in the rocks, of observed changes in continental contours 

 going on today, of erosion going on in coasts and streams, and of a 

 considerable array of facts derived from a study of other worlds than 

 ours in the making. The theory of geologic evolution meets with 

 scarcely any opposition today, although its foundations are no more 

 securely based than are those of organic evolution. 



In a sense the proofs of the atomic, ionic, and electron theories 

 are even less absolutely established than is that of organic evolution, 

 because no one has ever seen nor ever can see an atom, an ion, or an 

 electron. Chemical and physical fact . are rationalized by assuming 

 the existence of these units with their various properties. The only 

 evidences of the existence of atoms, ions, and electrons appear in the 

 facts that, on the assumption that they exist, the whole array of 

 observed chemical and physical phenomena are rationalized and 

 bound together into a coherent, consistent, and intelligible system. 

 In other words, with the atomic, ionic, and electron theories chemistry 

 and physics are highly rational sciences; without these theories the 

 phenomena of physics and chemistry would be a hopeless hodgepodge. 

 Yet who would say that these fundamental theories are absolutely 

 proved ? 



The only type of proof of phenomena that cannot be directly 

 observed or that pertain to the remote past is circumstantial proof. 

 By analogy we conclude that certain changes took place thus and so 

 in the past because we observe similar changes going on today. Every 

 past event has left a trace, and it is the task of the historian, anti- 

 quarian, or evolutionist to discover and to interpret these traces. Some- 

 times the traces exist as vestiges in modern life and are meaningless 

 unless related to their origin in the past. The task of the student of 

 organic evolution is to gather all of the traces of past changes both in 

 living creatures today and in the preserved remains of creatures of the 

 remote past. A collection of traces of evolution involves many 



