4 INTRODUCTION. 



We are fully aware of the fact that the writings of such ex- 

 tremists as Lamarck, Weismann, and de Vries have been very 

 useful in bringing adaptation, selection, and mutation to the 

 fore, and so stimulating discussion of the importance and the 

 relative role of these different processes in the making of spe- 

 cies. But we are, nevertheless, convinced that these striking 

 theories, which strain to make one process look important to 

 the exclusion of everything else, have had their day. Genetics 

 has been tamed. It is no longer the field where theorists of 

 fanciful and proselytic tendencies, war, and preach, and ignore, 

 each other's facts, but a regular inductive science, which 

 strives to take into account and correlate all the facts adduced 

 by Zoologists, Botanists, and other specialists, a science in which 

 experiments are constantly devised to get light on doubtful 

 issues. Genetics has definitely passed from the stage of the 

 book to the stage of the periodical. 



Geneticians nowadays, cannot continue to make a clever 

 point and by padding out the importance of some hitherto 

 little regarded truth, make believe, that they have discovered 

 the only cause of species-formation. One of the curious effects 

 of over-emphasizing a single process and trying to make it pass 

 for the whole of evolution, is obviously, that it is always neces- 

 sary to make far-reaching generalizations from a slender body 

 of facts. Or it is even necessary to invent a purely hypothetical 

 process, begging the question, to make the theory appear at 

 all plausible. 



Lamarck, wanting to convince the naturalists of his time, of 

 the effectiveness of individual adaptation in changing species, 

 had to assume the hereditary effect of such adaptations, and 

 even to-day we see whole institutions vainly trying by an 

 earnest application of their entire personnel, to adduce other 

 than dialectic proof of such an effect, casually assumed as 

 true by Lamarck, as an indispensable foundation of his theory 

 of evolution. 



Weismann, anxious to make us believe that selection on 

 ordinary variation was the sole cause for specific diversity, as 



