xii CONTENTS 



PAGE 



attitude to this question. Duration of gene activity. 

 Sphere of gene activity. Use and disuse. 



CHAPTER V. Theories of Evolution . . .108 



Faith the ultimate basis. VitaHsm and mechanism. Nat- 

 ural selection. Germinal selection. Intraselection. Coin- 

 cident selection. Validity of selection theories. Isolation, 

 geographic and biological. Results of isolation. Impotence 

 of selection and isolation to explain evolution. Mutations. 

 Mutations and selection. Orthogenesis. Cause of mu- 

 tations. Preadaptation. Inadequacy of germinal theories. 

 Lamarckian theory. Kinetogenesis. Parallel induction. 

 Insufficiency of all theories. 



CHAPTER VI. Evolution in Nature . . .143 



Usefulness of mutations. X-ray mutations. Mutations 

 and environment. Acquired characters. Hypothetical 

 analysis of trend of evolution. Existing species based on 

 acquired characters, on hereditary characters. Experi- 

 mental results: eye defects in rabbits; Daphnia; mice; 

 Simocephalus; flax. Possible methods of evolution in a 

 complex species. Difficulties of interpretation of natural 

 cases. Palaeontology. What is a new character? Emer- 

 gent evolution. Complexity of evolutionary processes. 



CHAPTER VII. The Organic Tendency . . 177 



Autonomy of the individual. Opportunism in evolu- 

 tion. Mind. Results of mental control. Favorable 

 orientation. Instinct. Self -maintenance the tendency of 

 living things. Changes the outcome of interacting herit- 

 age and environment. Environment a perpetual source 

 of change. Effects of environment on organism. Tend- 

 ency of organism to become independent. Universal 

 necessity for adaptive adjustment. Necessity for experi- 

 mental evidence. 



CHAPTER VIII. Our Future Course . . .201 



Both heritage and environment essential. Environ- 

 ment may be only directive but is a possible source of 

 hereditary change. Some factors of heritage depend on 



