TWO OBJECTIONS CONSIDERED 



adverse circumstances, transitional forms have 

 already been discovered in considerable num- 

 bers, while it is fair to expect that many more 

 will be discovered when by and by we have 

 come to know the earth's surface more inti- 

 mately. 



Of all the objections which have been urged 

 against the theory of natural selection, this ob- 

 jection, from the paucity of transitional forms, 

 is the least weighty, though probably the most 

 obvious. The second objection which we have 

 to consider, though less immediately obvious, is 

 more weighty ; and though there is no reason 

 for regarding it as insuperable, we must admit 

 that it has not yet been entirely disposed of. 

 This objection is implicated with the difference 

 between the morphological and the physiolo- 

 gical definitions of species, and is usually known 

 as the argument from the infertility of hybrids. 

 As ordinarily stated, indeed, this argument is 

 merely the expression of a sorry confusion of 

 ideas. By a curious misunderstanding the in- 

 fertility of the mule is often urged as a direct 

 objection to the Darwinian theory. But this is 

 putting the cart before the horse. It is not the 

 infertility of the offspring of the horse and the 

 ass which should be cited as an obstacle to 

 the theory of natural selection, but it is the fer- 

 tility of the offspring of the carrier-pigeon and 

 the pouter, or of the pouter and tumbler. Mor- 



63 



