viii PREFACE TO THE FIRST EDITION 
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 
