CHAPTER I 



INTRODUCTION 



Scientists have accumulated more accurate 

 information regarding the laws and the physical 

 basis of heredity in the last fifty years than the 

 world acquired in the preceding fifty centuries. 

 Indeed the most important part of this knowl- 

 edge has come to light within two decades. 

 Moreover it is knowledge of immense practical 

 value, the sort that will certainly affect human 

 life and racial destiny. This does not imply 

 that aU the problems of heredity are settled or 

 that our knowledge of its laws is complete: 

 far from it. No one realizes as well as the 

 student of these phenomena how fragmentary 

 and incomplete is our present knowledge, but 

 enough has been achieved to afford some 

 rational foundation for human action. It is 

 generally recognized that important discoveries 

 have recently been made along these lines, but 

 the prevailing ideas regarding these and their 



