4 Introductory [CH. 



transformation of masses of individuals has become an 

 established dogma. Systematists, entomologists or botan- 

 ists for example, are daily witnesses to variation occurring 

 as an individual and discontinuous phenomenon, but they 

 stand aside from the debate ; and whoever in a discussion 

 of evolutionary theory appeals to the definiteness of varietal 

 distinctions in colour for instance, or in form, as recognizable 

 by common observation without mechanical aid, must be 

 prepared to meet a charge of want of intelligence or candour. 

 This is no doubt a passing phase and will end so soon as 

 interest in the problems of evolution is combined with some 

 knowledge of variation and heredity. 



Genetic experiment was first undertaken, as we have 

 seen, in the hope that it would elucidate the problem of 

 species. The time has now come when appeals for the 

 vigorous prosecution of this method should rather be based 

 on other grounds. It is as directly contributing to the 

 advancement of pure physiological science that genetics 

 can present the strongest claim. We have an eye always 

 on the evolution-problem. We know that the facts we are 

 collecting will help in its solution ; but for a period we shall 

 perhaps do well to direct our search more especially to the 

 immediate problems of genetic physiology, the laws of 

 heredity, the nature of variation, the significance of sex and 

 of other manifestations of dimorphism, willing to postpone 

 the application of the results to wider problems as a task 

 more suited to a maturer stage. When the magnitude 

 and definiteness of the advances already made in genetics 

 come to be more generally known, it is to be anticipated 

 that workers in various departments of biology will realise 

 that here at last is common ground. As we now know, the 

 conceptions on which both the systematists and the specula- 

 tive biologists have based their methods need complete 

 revision in the light of the new facts, and till the possibilities 

 of genetic research are more fully explored the task of 

 reconstruction can hardly be begun. In that work of 

 exploration all classes of naturalists will alike find interest. 

 The methods are definite and exact, so we need not fear 

 the alienation of those systematists to whom all theoretical 

 inquiry is repulsive. They are also wide in their scope, 

 and those who would turn from the details of classification 



