58 DEVELOPMENT AND HEREDITY. 



From the facts in the previous paragraphs of this 

 chapter, it will be clearly seen that organisms do 

 not become what they are in their adult form, by a 

 simple unfolding of innate energy. Their develop- 

 ment, and even life itself, is dependent upon and 

 caused by the never-ceasing action of the forces 

 of their environment. As an eminent physiologist 

 has said, generation after generation are the same 

 because they live and develop under the same con- 

 ditions. If the forces of the environment change, 

 the growth of the organism must also change. 

 Hence the effects of domestication on animals 

 and plants, the degeneration of northern dogs, etc., 

 in tropical regions, and the modifications of feral 

 races. 



