HEREDITY 121 



will result in specially gifted human beings, but 

 there is no scientific basis for the belief that they 

 will always beget equally gifted children. 



This brings us to ask the question, Is there to 

 be further human progress? In so far as man's 

 body is concerned, it long ago became limited and 

 never has overstepped these barriers. There is 

 no reason to expect that it ever will. Conklin 

 calls attention to the marked restrictions that exist 

 in all forms of life in the following: "Among 

 animals no new phyla have appeared since the 

 vertebrates in the Silurian or perhaps even earlier; 

 no new classes since mammals in the Triassic and 

 birds in the Jurassic. In the evolution of animals 

 only about fourteen times in the whole history of 

 life have new phyletic paths been found and sever- 

 al of these were blind alleys that led nowhere. The 

 climax of the progressive evolution of fishes was 

 probably reached in the Devonian, of amphibians 

 in the Permian, of reptiles in the Mesozoic. In 

 all these classes the formation of new species has 

 been going on more or less continuously, but 

 progressive evolution in the sense of increasing 

 complexity or organization has reached or passed 

 its climax." It would seem, then, that man's 

 progress was restricted to intellectual activities 

 the discussion of which will constitute the main 

 theme of chapters IX and X. 



