4 Heredity and Environment 



evolution, the fact that essential and fundamental resemblances 

 exist among all kinds of organisms can not fail to impress 

 thoughtful men. Life processes are everywhere the same in prin- 

 ciple, though varying greatly in detail. All the general laws of 

 life which apply to animals and plants apply also to man. This 

 is no mere logical inference from the doctrine of evolution, but 

 a fact which has been established by countless observations and 

 experiments. The essential oneness of all life gives a direct hu- 

 man interest to all living things. If "the proper study of man- 

 kind is man," the proper study of man is the lower organisms 

 in which life processes are reduced to their simplest terms, and 

 where alone they may be subjected to conditions of rigid experi- 

 mentation. Upon this fundamental likeness between the life 

 processes of man and those of other animals are based the won- 

 derful advances in experimental medicine, which may be counted 

 among the greatest of all the achievements of science. 



Control of Development and Evolution. The experimental 

 study of heredity, development and evolution in forms of life be- 

 low man must certainly increase our knowledge of and our con- 

 trol over these processes in the human race. If human heredity, 

 development and evolution may be controlled to even a slight 

 extent we may expect that sooner or late'r the human race will be 

 changed for the better. At least no other scheme of social better- 

 ment and race improvement can compare for thoroughness, per- 

 manency of effect, and certainty of results, with that which at- 

 tempts to change the natures of men by establishing in the blood 

 the qualities which are desired. We hear much nowadays about 

 man's control over nature, though in no single instance has he 

 ever changed any law or principle of nature. What he can do is 

 to put himself into such relations to natural phenomena that he 

 may profit by them, and all that can be done toward the improve- 

 ment of the human race is to apply consciously to man those great 

 principles of development and evolution which have been at work, 

 unknown to man, through all the ages. 



