2 HEREDITY AND EUGENICS 



future development of the human race, which Sir 

 Francis Galton originally contemplated in the Eugenic 

 Movement. Popular writers frequently venture to 

 deny the importance of heredity to mankind. They 

 are willing to concede its cogency in animals, and, 

 in fact, practical breeders of horses and dogs and other 

 domestic animals rely upon heredity to perpetuate 

 even slight differences in their strains. But they are 

 often unwilling to accept for mankind the principles 

 of heredit}' which they themselves have practised 

 or seen in operation in other animals. Even those 

 w^ho recognise that the principles of heredity must be 

 the same for mankind as regards physical characters, 

 are sometimes inclined to deny that the same laws 

 hold for mental characteristics. 



It is therefore hoped that this book ma}^ help to 

 bring the reader to a truer perspective regarding the 

 nature and meaning of heredity, and its fundamental 

 bearing on the future of the human race. False 

 conceptions regarding inheritance are widespread, 

 and this is not surprising in view of the complexity 

 of the subject and the general lack of education in 

 the biological sciences. Only in the last tw^o decades, 

 through experimental investigations with plants and 

 animals, has any clear road been found through a 

 mass of complicated data. It may now be claimed, 

 however, that the general mechanism of heredity 

 is well understood in many cases, and although, as 

 in every science, complications continually arise with 

 further knowledge, the principles already understood 

 will form a sound basis for future advance. 



It is impossi-ble in this book to consider the whole 

 field of heredity in general terms. For that purpose, 

 reference ma}^ be made to various works on the subject 

 which have appeared in recent years, during which the 

 field of genetics has been an extremely active one. 

 In this w^ork an effort will be made to bring together 



