INTRODUCTION. 



THE origin of species, the way in which evolution has taken 

 place and is still progressing, seems, even now, to remain an 

 open question. So much so, that three absolutely diverse theo- 

 ries of evolution still find their adherents. These three main 

 theories are so different, that it would seem as if the real na- 

 ture of the process of species- formation must for ever remain 

 a subject for speculation only, and as if good facts are wholly 

 wanting. 



A minority of Biologists adhere to Lamarck's theory of the 

 inheritance of adaptative changes induced by the environ- 

 ment ; some incline to the view of Darwin and Weismann, that 

 natural selection on small, individual variations gradually 

 changes species, and still others believe with de Vries, that 

 new species spring into being spontaneously, by mutation, 

 saltation. Judging from this diversity of opinion, it would 

 certainly seem as if no important headway had been made 

 since Darwin. 



This is very surprising, when we see how in the last fifteen 

 years Genetics has become established as an actively develop- 

 ing branch of science, and counts by hundreds the Biolo- 

 gists who are engaged in genetical experimental investigations. 

 All the data thus acquired, should have their significance for 

 an insight into the process of evolution, the origin of species. 

 This reluctance on the part of Biologists in general, and of 

 Geneticists specially, to make an attempt to correlate the 

 facts so far obtained, and to find out whether they shed any 

 new light on the problem how new species may originate, is 

 caused mainly, we hope, by the very diversity of the three 

 above-named evolution-theories. Their great diversity neces- 



