THE DARWINIAN THEORY 31 



of the century, for he began with forms of life which had previously 

 been markedly neglected by science, the varieties of our domesticated 

 animals and cultivated plants. 



Previously these had been in a sense mere step-children of 

 biology, inconvenient existences which would not fit properly into 

 the system, which were therefore as far as possible ignored or dis- 

 missed as outside the scope of ' the natural/ because it was difficult 

 to know what else to do with them. I can quite well remember that 

 even as a boy, I was struck by the fact that one could find nothing in 

 the systematic books about the many well-established garden forms 

 of plants, or about our domestic animals, which seemed to be reo*arded 

 as in a sense artificial products, and as such not worthy of scientific 

 consideration. But it was in these that Darwin particularly inter- 

 ested himself, making them virtually the basis of his theory, for he 

 led up from them to the very principle of transformation, which was 

 his most important addition to the earlier presentations of the 

 Evolution theory. 



He started from the existence of varieties which may be 

 observed in so many wild species. His line of thought was somewhat 

 as follows : If species have really arisen through a gradual process 

 of transformation, then varieties must be regarded as possible first 

 steps towards new species ; if, therefore, we can only succed in finding 

 out the causes which underlie the formation of any varieties what- 

 ever, Ave shall have discovered the causes of the transformation of 

 species. Now we find by far the greatest number of varieties, and 

 the most marked ones, among our domesticated animals and plants, 

 and unless we are to assume that each of these is descended from 

 a special wild species, the reason why there has been such a wealth of 

 variety-formation among them must lie in the conditions which 

 influence the relevant species in the course of domestication ; and 

 it remains for us to analyse these conditions till we come upon the 

 track of the operative factors. With this conviction, Darwin devoted 

 himself to the study of domesticated animals and plants. 



The first essential was to prove that every variety had not 

 a separate wild species as ancestor, but that the whole wealth of our 

 domesticated breeds originated, in each case, from one, or at least from 

 a few wild species. Of course I cannot here recapitulate the multi- 

 tudinous facts which were marshalled by Darwin, especially in his 

 later works, notably his Animals and Plants under Domestica- 

 tion, but this is not necessary to an understanding of his conclu- 

 sions, and I shall therefore restrict myself to a few examples. 



Let us take first the domestic dog, Canis familiar is, Linne\ We 



