48 THE PROBLEMS OF EVOLUTION 



modification of either material or forces will pro- 

 duce a change in the organism? It seems wholly 

 probable, but we encounter a specific problem 

 here which is quite different from any associated 

 with inanimate objects. The matter of which 

 living organisms are composed possesses a power 

 of self-determination through which it is protected 

 from passive molding by environmental forces. In 

 the course of evolution, as we have noted, organ- 

 isms tend to secure more and more independence 

 of environmental conditions through the autono- 

 mous activities of their own bodies. Outer forces 

 cannot fail to bear upon living things, but internal 

 forces also affect them. Our problem necessitates 

 inquiry into the effectiveness of these various forces 

 in the shaping of organisms. 



In approaching such an inquiry it is pertinent 

 to note that the discoveries of modern physics 

 disclose the existence of internal forces in inani- 

 mate things which we cannot fail to consider. 

 Chemical changes are brought about by the action 

 of physical forces, such as X-rays, but modern 

 physics has shown that change may take place as 

 a result of internal forces. Atoms of some of the 

 heavier elements, such as uranium, are constantly 

 undergoing disintegrative radiation which trans- 

 forms them ultimately into lead. The concept of 

 independent internal activity in living matter is 

 therefore not impossible. It leads to the admission 



