PREFACE 



This book has been written partly by the accident of 

 circumstances and partly by request. It is based 

 upon a couple of articles which appeared in the 

 Eugenics Review for January and April, 1920, and 

 part of it was written during a holiday in America in 

 1 92 1. Although m}' present interests are occupied 

 with the field of modern botany, I was impelled to 

 write this book by my interest in Eugenics, which is 

 in turn founded upon a knowledge of genetics. The 

 actual writing of it was, however, only made possible 

 by the many friends in various parts of the world who 

 have sent me their publications. 



It is clear to scientific men, although rarely to 

 statesmen and law-makers, that any intelligent 

 attempt to improve the conditions and qualities of the 

 human race must be founded upon some knowledge 

 of the manner in which these qualities arise and are 

 inherited and maintained or lost. In this book I have 

 confined myself as strictly as possible to an examina- 

 tion of the facts of human inheritance, in so far as 

 they are at present known, and I have laid particular 

 emphasis — possibly too much — upon the many cases 

 now known of Mendelian inheritance in man. This 

 is not on account of any partiality for this particular 

 form of inheritance; but because the Mendehan 

 differences are clear cut and more easily recognised, 

 and the manner of their inheritance is more easil}^ 

 traced and analysed and investigated than that of 

 differences which can only be recognised as quantita- 



vii 



