EVOLUTION IN NATURE AND UNDER DOMESTICATION. 239 



one without crossing of some kind at the outset. As in the case 

 of the fowl and the pigeon, we do not need to look for wild rab- 

 bits or hares with the markings of the "Papillon", or with ears 

 that measure 24 inches, but we may rest assured that crossing 

 with even a very similar American cotton-tail, might produce 

 such aberrant characters. 



The thesis, that no extensive variability, and therefore no 

 formation of very many different domestic species is possible 

 within one good single species, is further strenghthened by 

 comparing the variability in such poly-genetic groups as the 

 swine, cattle, dogs, to those animals that have been long domes- 

 ticated, but which cire almost certainly descended from one 

 wild species, such as the guinea-fowl and the pea cock. We know 

 two recessive colours in the guinea-fowl and three in the pea- 

 cock, and no structural variations whatever, and we may with 

 some reason assume that these few variations are the result of 

 loss-mutations. 



Contrary to the belief that the semi-domesticated state in 

 which guinea-fowl and pea-fowl have been kept, hindered them 

 from varying, as they thus were not subjected so much to 

 changed conditions and different food, we are convinced that 

 these animals are only semi-domesticated because they did not 

 vary through crossing. If they had been crossed, each with a 

 related species, they would not only have varied in shape and 

 colour, but also in their adaptability to life under intensive 

 cultivation, and selection would speedily have made them 

 domestic animals. 



There are great differences between the course of evolution 

 in domestic plants and animals, and in species under nature. In 

 natvire, every species consists of a multitude of like individuals, 

 and matings are greatly a matter of chance. This results in a 

 great stability, and it makes selection of any kind ineffective 

 within a species. Natural selection, plays its role evidently at 

 the origin of new species, that is to say,' that natural selection 

 will evidently help to determine -the type, for which an isolated 

 group of individuals, with a sufficiently laige total potential 



