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M 



Chapter 13 



The Inward Urge to Change 



"]{[ OST people have no great difficulty in thinking 

 of the material universe as in constant flux. We 

 accept the universality of cause-and-effect rela- 

 tionship, and this furnishes a satisfactory " explanation " of 

 the physical events. We are satisfied to accept the interpre- 

 tation of what happens on a strictly mechanistic basis. We 

 have confidence that " science " can measure and predict, 

 and eventually control, the purely physical or chemical re- 

 alities of the world. 



The difficulty arises when we attempt to think mechan- 

 istically of living things, of their activities as individuals, 

 of their adaptations to their complex surroundings, of their 

 rise and extinction in the past, and of the suggested ap- 

 pearance of new forms from different parental forms. The 

 convergence of the evidences from various branches of 

 scientific study leaves no doubt in the mind of the biologist 

 or of the paleontologist that evolutioit (in the sense here 

 used) has actually taken place. The numerous attempts to 

 explain what seems to have happened have not, however, 

 united the opinions of informed specialists on a scientific or 

 cause-and-effect theory. Each of the more prominent the- 

 ories is plausible enough, but none accounts for all of the 

 facts in a satisfactory way. 



Divergent Theories 



Lamarck's theory, the transmission of the effects of 

 use and disuse, stands to reason, as we say. Nothing could 

 be more satisfactory than this logic: just as the individual 



