EXPLANATIONS OF EVOLUTION 335 



developed. Others, important before, would be now less 

 called upon, and would begin to decline. Thus the animal 

 would begin to change, and these changes would be handed 

 down to its progeny and increased by them, and so on until 

 practically a new animal would be the result. 



It is evident that this explanation depends upon what is 

 called the inheritance of "acquired characters"; for the 

 progeny must start with all the gains acquired by the 

 parent, and not be compelled to start over again. But, 

 now that it is generally agreed that such acquired charac- 

 ters are not inherited, the "theory of appetency" finds little 

 support. It has recently been revived in a modified form, 

 but this lies outside our purpose. 



3. The next epoch was by far the most important one 

 in its results. It was introduced in 1859 by the appearance 

 of a book by Charles Darwin, entitled "The Origin of 

 Species by Means of Natural Selection." In this case also 

 the theory was announced by another observer independ- 

 ently, Alfred Russel Wallace. When Wallace learned that 

 Darwin had had the theory under consideration for twenty 

 years, and was prepared to present it based upon a won- 

 derful collection of observations, he generously withdrew 

 from its further development. 



This epoch was the most important one because the new 

 theory revolutionized biology, and in fact revolutionized the 

 point of view in almost every department of thought. The 

 greatness of Darwin really consisted not so much in his 

 theory as in what he set men doing. He called his ex- 

 planation " the theory of natural selection," but it has been 

 freely spoken of as "Darwinism." It has been the con- 

 spicuous explanation of evolution for fifty years, and even 



