viii PREFACE 



^ The rediscovery of Mendel's law some seven years 

 ago led to a complete change in our attitude towards 

 the problems of variation, heredity, and evolution ; 

 and the new method of study thus introduced has 

 rendered possible a renewal of the attack upon these 

 problems with increased vigour and with remarkable 

 results. At the present time this activity may be 

 said to have its centre in the school of genetic research 

 founded at Cambridge by the independent energy of 

 Mr. Bateson. So far-reaching are the results already 

 arrived at by Mr. Bateson and others, both in their 

 scientific interest and in their probable influence upon 

 human affairs, that it seemed desirable to give an 

 immediate account of these and of kindred lines of 

 recent study, even though the rapid progress which is 

 a characteristic manifestation of this department of 

 science must render any such attempt a more or less 

 transitory one. 



Whilst I was still engaged upon my task, the first 

 volume of Dr. Lotsy's admirable ' Vorlesungen iiber 

 Descendenztheorien ' made its appearance. But for 

 the fact that most of the following pages had then 

 already been written, I might have hesitated to pursue 

 my project, since a book not altogether unlike the 

 present might be produced by the comparatively simple 

 process of making a series of judicious extracts from 

 Dr. Lotsy's work. The latter is, however, in the 

 German language, and on a considerable scale, so that 

 there seemed still to be room for an introduction to 



