CHAPTER 20 

 THE THEORY OF EVOLUTION 



Organic Evolution may be defined as the historic process of 

 change by which existing animals have reached their present 

 state. If living things have had such a history, it has been a 

 process involving many milhons of years. This doctrine is in 

 marked contrast with the theory that animals and plants orig- 

 inated in their present form and within a comparatively recent 

 poriod. Evolution involves more than the history of organisms, 

 however. Astronomy tolls us that our solar system probably 

 originated through countless years, as other solar systems seem to 

 be originating at the present day; and Geology that our planet 

 has had a long history. The doctrine of Evolution therefore 

 embraces Inorganic Evolution, which includes the Cosmic Evolu- 

 tion of which Astronomy teaches, and Geologic Evolution; and, 

 also. Organic Evolution, or the evolution of hving things. 



As we are primarily concerned with Organic Evolution, the dis- 

 cussion cannot be extended to the inorganic field. It will be under- 

 stood, however, that evolution is the scientist's answer to the ques- 

 tion of how the world about us — sun and stars, mountains and 

 oceans, animals and plants — has reached its present form. Evolu- 

 tion is, in fact, the entire process of change that is going on in the 

 universe and that is believed to have been in operation for as long a 

 period as the mind can picture. As a corollary, it may be supposed 

 that this process, at least insofar as it affects inorganic bodies, 

 will go on forever. Hence, the doctrine involves events that have 

 no recognizable beginning or end in time or space, since they include 

 the changes by which suns and planets as well as hving beings 

 have come to exist and will exist in the future. 



The Origin of Life 



Time of Origin. — The period at which protoplasm appeared 

 upon the earth must have been remote, since the age of the fossil- 



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