X INTRODUCTION 



tion that evolutionary change is bound to occur, under whatsoever 

 circumstances. Evolution, however, is not the notion that organisms 

 are bound to change regardless of conditions. If an animal is adapted to 

 a particular environment, as the monkey is to the forest, and the forest 

 persists, we should not expect the monkey to change. It may be said 

 in this connexion, however, that evolution is not the theory that man 

 came from a monkey, but that the bodies of the two have had a common 

 animal origin. 



Evolution is sometimes said to be "only a theory," as if it were no 

 more than an unfounded guess or pure assumption. On the contrary it 

 is doubtful if any other scientific theory has greater factual support. 



A frequent objection raised against evolution is that "it cannot explain 

 the origin of life." It may candidly be admitted that we know nothing 

 about the origin of life. But the primary question of evolution is not how 

 life began but how organisms have changed since their origin. The 

 geological record leaves us in no doubt as to the fact of change. As to the 

 origin of life, L. J. Henderson is probably justified in saying that "any 

 theory about the origin of life is nothing but an unfounded guess." 



Again, it is charged that the evolution theory "degrades" man by 

 making a monkey of him. In reply to this supposed objection it may be 

 said that the differences between man and monkeys obtain whatever 

 may have been their origin. "A man's a man for a' that." Values are 

 not determined by origins. The value of the Venus of Melos is not 

 afifected by the fact that the block of marble from which the statue was 

 carved came from a quarry. 



Our ignorance of the causes of evolution has been considered an objec- 

 tion to the theory. It must be admitted that it has been found easier to 

 prove that evolution has taken place than to explain how it has been 

 brought about. Undoubtedly the nineteenth century belief that Darwin's 

 hypothesis of natural selection explained organic evolution led men to 

 accept this theory more readily than they otherwise would have done. 

 Nevertheless, the case for evolution does not depend upon the ability to 

 state its cause any more than the existence of light depends upon our 

 ability to explain how it reaches the earth. 



Of the hypotheses advanced to explain evolution, three have best 

 survived criticism. Briefly stated they are: 



I . The Lamarckian hypothesis assumes that organic evolution is due 

 to four factors: 



1. The will to live 



2. The use or disuse of organs 



3. The influence of environment 



4. The inheritance of the bodily modifications due to use or disuse or to the influence 

 of environment. 



