2 INTRODUCTION. 



sarily leads to the idea that theories of evolution must always 

 be essentially speculative. 



We hope that this failure of Biologists in general to take an 

 interest in the evolution-problem, is mainly caused by their 

 unconscious recognition of the one-sidedness of the above- 

 named theories, that each tries to explain all evolution by one 

 omnipotent agency to the exclusion of all other causes. The 

 spirit in which Darwin attacked the problem is hard to emulate. 

 Few dare to presume they have the required broadness of vision 

 to try what Darwin attempted, and it is not without a feeling of 

 hesitation that one undertakes even to begin work of this kind. 



But at times the feeling will not down, that a great number 

 of eminent and able Biologists utterly fail to understand in 

 how far their results have value in themselves, and in how far 

 they are but building-stones. Many do not seem to see, that, 

 without a timely attempt to utilize their results in construct- 

 ing a coherent whole of a higher order, much detail is utterly 

 wasted, being without significance in itself. It is very evident 

 that many fail to see the forest because of all the trees. 



There is no real spirit of subordination of the different genet- 

 ical investigations to the main problems of evolution, in the 

 work of any but Bateson and a few others. What we need from 

 time to time, is to pause, and try to see what all the others are 

 doing, where they are going, what work is left undone, and 

 where work is unnecessarily duplicated. 



This book is written with the purpose of showing that con- 

 ditions are not so hopeless, that, especially in the last decade, 

 great advances have been made in our knowledge concerning 

 everything pertaining to evolution. 



The existence of Genetics as a science, which is being devel- 

 oped in a systematic way, so, that the majority of the students 

 continue and amplify the work of others, dates only from the 

 last fifteen years. 



Genetical questions have always interested all sorts of Phil- 

 osophers; they have also interested Botanists and Zoologists. 

 But it is remarkable to note how few of these Biologists have 



