CHAPTER XII 

 EVOLUTION 



Among all organisms which we can carefully watch and study 

 new variations are continually appearing and being inherited" 

 This fact at once suggests that living things are not constant 

 and changeless in their characteristics but that they may undergo 

 a certain degree of permanent modification as the generations 

 succeed each other. A glimpse at the remarkable development 

 of our domestic plants and animals, since man first began to 

 utilize them and to improve them by selection, shows the possi- 

 bilities of change which exist among organisms. The difference 

 between the small, sour prototype of the apple, for instance, and 

 our modern large and delicious varieties is so great that we can 

 hardly recognize the relationship between the two. In fact, 

 many of our cultivated forms have progressed so far under human 

 guidance that we do not know what their wild ancestors were. 



Since the days of the Greeks, philosophers have often specu- 

 lated as to the possibility that the whole organic world — plants, 

 animals and man — has reached its present state through a gradual 

 evolution from far simpler forms, perhaps ultimately from organic 

 matter. It is only within the last century, however, that the 

 subject of evolution has descended from these clouds of specula- 

 tion and become a problem for scientific study. Little by little, 

 evidence has been accumulating that progressive change has 

 actually taken place, and that the plants and animals which we 

 now know differ radically from their ancestors in past ages. As 

 to just how this has been accomplished biologists are still far 

 from agreed, but as to the fact of evolution there is now practi- 

 cally no doubt in the minds of scientific men. An insistence that 

 every species was specially and suddenly created in exactly the 

 form which it now displays has given way to the more profound 

 conception of the world as the theatre of a slow but steady upward 

 progress from lower to higher types of life. 



Evidences for Evolution. — The lines of evidence on whicli the 

 belief in evolution is based are various, and we shall briefiy 

 discuss a few of them. 



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