HEREDITY AND EUGENICS 



CHAPTER I 



INTRODUCTION 



The central problem of evolution is still the nature 



and causes of variation, while the practical problems 



of eugenics centre about heredity. Variation in past 



ages has already endowed the human race with an 



almost infinite variety of types and characters, 



many of the latter alternative in their inheritance. 



We have only to compare those we know best with 



their relatives and ancestors to realise how minute 



are the resemblances and differences which ma}^ be 



handed on to descendants and collateral lines. These 



are, no doubt, chiefly a matter of biological inheritance, 



though similarity of environment may play a part 



in certain cases. Probably in no other species of 



animal or plant does the number of differences between 



individuals approach the number to be observed in 



man. This is to be expected, because of the mental 



and physical complexity of the human organism; but 



it does not imply greater intrinsic variability than in 



other animals or plants. 



Given this enormous complexity of types in the 



human species, and the inheritance of the innumerable 



differences involved, it follows that the matings of 



the present generation determine the characteristics 



which will be handed on to future generations. A 



knowledge of inheritance must, therefore, form the 



basis of any enlightened attempt to influence the 



I I 



