CHAPTEE X 



PRESENT ASPECTS OF THE THEORY OF EVOLUTION 



IN all our study we have taken for granted the 

 truth of the theory of evolution. If you are not al- 

 ready persuaded of this by the writings of Darwin, 

 Wallace, and many others, no words or arguments of 

 mine would convince you. We have used as the foun- 

 dation of our argument only the fundamental proposi- 

 tions of Mr. Darwin's theory. 



But while all evolutionists accept these propositions 

 they differ more or less in the weight or efficiency 

 which they assign to each. In a sum in multiplication 

 you may gain the same product by using different 

 factors ; but if the product is to be constant, if you 

 halve one factor, you must double another. Evolution 

 is a product of many factors. One evolutionist lays 

 more, another less, emphasis on natural selection, ac- 

 cording as he assigns less or more efficiency to other 

 forces or processes. Furthermore, evolutionists differ 

 widely in questions of detail, and some of these sub- 

 sidiary questions are of great practical importance and 

 interest. It may be useful, therefore, to review these 

 propositions in the light of the facts which we have 

 gathered, and to see how they are interpreted, and what 

 emphasis is laid on each by different thinkers. 



The fundamental fact on which Mr. Darwin's the- 

 ory rests is the " struggle for existence." Life is not 



