Epilogue: What Gomes of Studying Vertebrates !><) ( ) 



rests upon an insecure biologic foundation. The role of "use and dis- 

 use" in evolution of organs is highly problematic. 



The primary factor in the evolution of the human environment is 

 somehow associated with the brain. To what extent, if any, structural 

 changes have occurred in the brain since the earliest days of man it is 

 impossible to say. Human evolution is essentially an evolution, not of 

 organs, but of ideas which find their expression in adaptive modifica- 

 tion of the physical environment, and in the structure and relations of 

 social and political groups of human individuals. 



VELOCITY OF HUMAN EVOLUTION 



In contrast to the evolution of bodily structure, human evolution 

 is progressing at tremendous velocity. Some reason for this may be 

 discerned. Bodily changes acquired during the lifetime of an individual 

 animal are, so far as is known, not inherited by the offspring. Results 

 of training and learning by experience are not transmitted to offspring. 

 A dog may be taught tricks but the puppies must likewise be taught. 

 An innate capacity for learning tricks is inherited, but not the tricks. 

 Protoplasm is chemically a highly unstable substance, but the structure 

 of the organisms which are constituted of protoplasm possesses an 

 extraordinary degree of stability. Structural adaptations which have 

 somehow become fixed or determined in the germ-plasm are not easily 

 and quickly changed. Mutations occur, but it is safe to say that no 

 single mutation produced a first amphibian, or a feather in place of a 

 reptilian scale. It is likely that climatic or other environmental changes 

 caused the downfall of the mighty dinosaurs and other Mesozoie 

 reptiles, unable to adapt themselves even though the changes must 

 have taken place very slowly over a period of many tens of thousands 

 of years. The processes of embryonic development are especially con- 

 servative. The fishlike characteristics of the early embryo have presum- 

 ably persisted for hundreds of millions of years from the earliest days of 

 vertebrates down to the mammals and birds of the present. 



Whereas bodily characteristics acquired by an adult animal are not 

 transmitted to offspring, environmental structures and conditions pro- 

 duced by a human individual or group are "inherited" by the succeed- 

 ing generation. It is not necessary for the new generation to rediscover 

 how to use fire and make electricity, or to reinvent motors and tele- 

 phones. The child of the cave man perhaps played with a toy club. 

 The modern child's toys are models of automobiles, airplanes, and 

 telephones. During the educational years of childhood and youth, 

 the new individual acquires (to the limit of his intellectual capacity) 

 knowledge of all that mankind, from cave man to the present, has done 

 to acquaint himself with his environment (science), to make it serve 



