6 INTRODUCTION. 



Weismann and that of de Vries, clearly shows how insuffic- 

 iently Zoologists and Botanists know each other's facts. It 

 further shows, that Genetics as a science ought not to be rank- 

 ed, and ought not to he taught in Universities as a branch of 

 ZoQlogy or of Botany or of Agriculture, but should be a thing 

 by itself. 



Darwin was chiefly concerned with evolution, £ind he tried 

 to make his, theories about evolution fit all the facts. Zoological 

 and Botanical, of variation and heredity, which were known 

 in his day. The Geneticians after Darwin, have not continued 

 his work in the same spirit. Their theories have been chiefly 

 theories of heredity, and their ideas about evolution have too 

 often been generalizations of a small body of facts, either 

 Zodlogical or Botanical. No all-round Genetician, familiar 

 with the history of continual change of the different species of 

 domestic animals, would have generalized the facts observed 

 by de Vries in Oenothera into a theory of evolution as this 

 author did, neither would it be possible, that a Genetician 

 conversed with the results of selection in the lines of wheats 

 started by Louis de Vilmorin and the recent results of pure- 

 iine-breeding, made a theory of evolution like that of Weis- 

 mann. 



Judging from the little interest of the latter-day Geneticians 

 in problems of evolution, it would seem as if the enormous 

 progress which Genetics as a science has made in the last fif- 

 teen years, did not help us to a clearer insight into just this 

 lundamental problem, how species have originated. 



It seems worth while to us, to find out, in how far the new 

 facts which these fifteen years of genetical experiments have 

 given us, can help us further on the road taken by Darwin. 

 Darwin's views about evolution were in"^ accordance with the 

 state of knowledge about variation and the effect of selection 

 of his period. It is time to see, whether it is not possible to 

 clear up some points which were dark to Darwin. It seems sur- 

 prising, that after all these years of diligent work in the study 

 of Genetics, we must still start from Darwin's ideas about evo- 



