CHAPTER XXXIV 

 EVIDENCES OF EVOLUTION 



Evolution Defined. — For many centuries it was 

 generally believed that every species of animal and plant 

 was a special act of the Creator, and long ago was placed 

 in its present perfected state and in the same locality it 

 now occupies. According to this view a species is un- 

 changeable. The fish is forever adapted for a life in the 

 water, a mole for tunneling in the earth, and a bird for an 

 existence in the air. This view of the organic world fails 

 to take into account a large body of facts which is now 

 thought to run counter to such a belief, and which is ex- 

 plained by the modern biologist on the principle of evolu- 

 tion. According to this doctrine, a species amid changing 

 conditions is not fixed, but on the contrary is under- 

 going alterations from generation to generation. The 

 changes generally are very slow and almost imperceptible 

 during a brief period, but where the remains of countless 

 generations have been preserved in fossil form during 

 millions of years, the transformation is clear and un- 

 mistakable. It is also true that the further back the his- 

 tory of a species is traced the simpler the ancestral type 

 becomes. In other words, if the geological record were 

 complete it would be found that each of the thousands 

 of species of animals and plants is the descendant of one 

 simple form of life, or at most, of a very few. Evolution, 

 therefore, is the derivation of complex, high, and special- 

 ized species from simple, low, and generalized ancestors. 



Sources of Evidence. — This gradual change or evolu- 

 tion of living things is to the trained biologist an estab- 

 lished fact. To him the evidence in support of such a be- 



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