CREATION BY EVOLUTION 



more than Rome was, but they are being made here and now, 

 and many biologists are studying the steps, conditions, and 

 causes of evolutionary changes in animals and plants. All 

 such study of contemporary evolution is necessarily a study 

 of successive generations of individuals, and all analytical 

 or experimental study of the causes of evolution resolves 

 itself into a study of the factors involved in the genesis of 

 individuals; there is no other possible method of approaching 

 the problem. The study of the factors involved in the gen- 

 esis of individuals under various conditions of inheritance 

 and environment reveals all that can certainly be known 

 regarding the methods and causes of the evolution of races 

 and species. 



The causes of the development of an individual or of the 

 evolution of a species are twofold, internal and external. 

 The internal causes are represented by the organization of 

 the germ cell, the external by surrounding conditions; the 

 internal causes may be called heredity, the external causes 

 environment. 



An egg cell, like every other kind of cell, functions in 

 response to stimuli. When a muscle cell is stimulated it 

 contracts, when a gland cell is stimulated it secretes, when an 

 egg cell is stimulated it develops. The stimulus comes, in 

 the first instance at least, from the environment; an egg will 

 start to develop only when stimulated by a spermatozoon or 

 by certain salts or chemicals, or by changes in temperature, 

 and It will continue to develop only so long as environmental 

 stimuli of water, oxygen, food, temperature, etc., remain 

 favorable to its development. 



The character of development depends primarily upon 

 the nature (that is, the hereditary organization) of the egg 

 concerned, and secondarily upon the environmental stimuli. 

 The former determines all the possibilities of development 



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