112 CONDITIONS AFFECTING THE 



Now, the next problem that lies before us — and it 

 is an extremely important one — is this : Does this selec- 

 tive breeding occur in nature ? Because, if there is no 

 proof of it, all that I have been telling you goes for 

 nothing in accounting for the origin of species. Are 

 natural causes competent to play the part of selection 

 in perpetuating varieties? Here we labour under very 

 great difficulties. In the last lecture I had occasion 

 to point out to you the extreme difficulty of obtaining 

 evidence even of the first origin of those varieties which 

 we know to have occurred in domesticated animals. 

 I told you, that almost always the origin of these varie- 

 ties is overlooked, so that I could only produce two 

 or three cases, as that of Gratio Kelleia and of the 

 Ancon sheep. People forget, or do not take notice of 

 them until they come to have a prominence ; and if 

 that is true of artificial cases, under our own eyes, and 

 in animals in our own care, how much more difficult 

 it must be to have at first hand good evidence of the 

 origin of varieties in nature ! Indeed, I do not know 

 that it is possible by direct evidence to prove the origin 

 of a variety in nature, or to prove selective breeding ; 

 but I will tell you what we can prove — and this comes 

 to the same thing — that varieties exist in nature within 

 the limits of species, and, what is more, that when a 

 variety has come into existence in nature, there are 

 natural causes and conditions, which are amply com- 

 petent to play the part of a selective breeder ; and al- 

 though that is not quite the evidence that one would 

 like to have — though it is not direct testimony — yet it 

 is exceeding good and exceedingly powerful evidence 

 in its way. 



As to the first point, of varieties existing among 



