292 Theories of Evolution and Creation 



ments, as well as to explain what has already happened. For 

 example, a complete theory of evolution ought to be ap- 

 plicable to the breeding of plants and animals; to the res- 

 toration of a living population to a desert or denuded 

 area; to the restoration of the balance of nature brought 

 about by the introduction of new species into a given 

 area or by the elimination of existing species; and to the 

 many problems of human migration and social control of 

 differential birth rates — the problems of eugenics or race 

 improvement. 



Special Evolution Theories 



There are several types of theories calculated to explain 

 how the world of plants and animals came to be what it is, 

 what makes it constantly change. Some theories attempt 

 merely to interpret certain kinds of facts in terms of natural 

 processes, uniform results of uniform causal forces. Others 

 attempt to be more comprehensive and to explain all of the 

 principles. There are three major facts to be accounted for: 

 the fact that living things are adapted; the fact that there 

 is variation; and the fact of heredity. 



Adaptation has been attributed to the essential nature 

 of protoplasm or living matter, an ultimate fact like mass 

 or extension. That is to say, it has been accepted as given 

 without any attempt at further explanation or analysis. It 

 has also been attributed to an inner striving or effort, which 

 is hardly to be distinguished from the first. Lamarck as- 

 sumed the presence of this innate principle in the first living 

 things created, and explained the further development of 

 mechanisms and functions during the evolution of plants 

 and animals as the result of the inheritance of the gains due 

 to the exercise of this primary adjustability. Darwin ac- 

 counted for adaptation by assuming fortuitous variation as 

 a universal fact of living matter, and the selective effect of 

 natural conditions as the means of eliminating the relatively 

 less fit. Natural selection or survival of the fittest accounts 



