108 CONDITIONS AFFECTING THE 



to this check. In crossing the breeds between the Fan- 

 tail and the Pouter, the Carrier and the Tumbler, or 

 any other variety or race you may name— so far as we 

 know at present — there is no difficulty in breeding to- 

 gether the mongrels. Take the Carrier and the Fan tail, 

 for instance, and let them represent the Horse and the 

 Ass in the case of distinct species ; then you have, as 

 the result of their breeding, the Carrier-Fantail mon- 

 grel, — we will say the male and female mongrel, — and, 

 as far as we know, these two when crossed would not 

 be less fertile than the original cross, or than Carrier 

 with Carrier. Here, you see, is a physiological con- 

 trast between the races produced by selective modifica- 

 tion and natural species. I shall inquire into the value 

 of this fact, and of some modifying circumstances, by 

 and by ; for the present I merely put it broadly before 



you. 



But while considering this question of the limita- 

 tions of species, a word must be said about what is 

 called Recurrence — the tendency of races which have 

 been developed by selective breeding from varieties to 

 return to their primitive type. This is supposed by 

 many to put an absolute limit to the extent of selective 

 and all other variations. People say, "It is all very 

 well to talk about producing these different races, but 

 you know very well that if you turned all these birds 

 wild, these Pouters, and Carriers, and so on, they would 

 all return to their primitive stock." This is very com- 

 monly assumed to be a fact, and it is an argument that 

 is commonly brought forward as conclusive; but if 

 you will take the trouble to inquire into it rather closely, 

 I think you will find that it is not worth very much. 

 The first question of course is, Do they thus return to 



