CHAPTER XXIX. 

 THE EVOLUTION OF ANIMALS. 



377. In the preceding pages the words evolution and 

 development have been used frequently, but no effort 

 has been made to define or justify them. In all that 

 has been said it has been assumed that the animals now 

 on the earth have come to their present condition of 

 varity and complexity by natural growth and develop- 

 ment, rather than by outright creation as we find them 

 now. This has been assumed, not because there can be 

 any complete demonstration of the view, but because it is 

 more in accordance with the facts as we find them than 

 any other theory which has been offered. 



The student is now in a position to study the question 

 of evolution more broadly, and to appreciate a more 

 full statement of it. 



378. The Meaning of Evolution. There is a good deal 

 of haziness in the thought of people generally as to just 

 what the zoologist means by evolution. Evolution is 

 not in any sense a cause; it is a term for a process, for the 

 way in which present conditions have come about. 

 Briefly, the most important elements in the thought of 

 evolution are gradualness and naturalness. In more de- 

 tail, the following features may be said to belong to the 

 idea of evolution: 



i. All life, so far as we can know, has come from pre- 

 existing life. This year's animals are descended from 

 380 



