58 the president's address. 



vary requisite to support Darwin's theory, we are apt to forget how 

 great this is. We hardly ever saw two human faces exactly 

 alike, and the same is doubtless true of animals if observed equally 

 closely. Everyone knows his own dog, and a skilled shepherd 

 knows each sheep. The two sides of the body usually vary greatly, 

 so that a man with the two rms the same length and the two legs 

 similarly corresponding is very rare, and although we are actually 

 all artificially taught to write the same way, we all write different 

 hands. Now what are the main objections ? Firstly, to my mind, 

 both to evolution and the explanation, stands the sterility of 

 hybrids. It is extremely difficult to answer this, but we may observe, 

 firstly, that it is only in the case of the Vertebrata and some plants 

 that we really know whether they are fertile or not ; as to other 

 groups, we are ignorant on the subject. Secondly, we are apt to 

 argue in a circle ; we are inclined to take the fertility or sterility 

 of hybrids as a test of species, and then to cite our classification to 

 prove that hybrids between different species are sterile. Moreover 

 the laws of sterility and the reverse contain many things 

 we do not understand. The Mexican Axolotl has been proved 

 to be an immature form of Amblystoma, but it is sexually 

 fertile in the Axolotl stage, and Amblystoma bred from 

 Axolotl is almost, but not quite sterile, while other Ambly- 

 stoma are freely fertile. Then there is reason to suppose that a 

 hybrid can to some extent fertilize one of the original species, 

 although the embryo does not usually reach maturity. Another 

 objection, to the explanation only, is the existence of neuter insects. 

 It is very difficult to see how these can have been produced by 

 natural selection, as they cannot ever have reproduced their kind. 

 This difficulty appears to have been so strongly present to 

 Darwin's mind that it almost shook his faith in his own theory ; 

 he succeeded finally in satisfying his own mind, but perhaps he was 

 not as happy in explaining this to his readers as he was in most 

 other cases. There is the difficulty why similar forms were not 

 produced in greater numbers by the same conditions. The oft-quoted 

 neck of the giraffe is a good example ; there are not more vertebrae 

 in it than in shorter necks, and Darwin reasonably says that it must 

 have been an advantage to a creature inhabiting a country liable to 

 drought to be able to browse on the leaves of trees when grass failed, 

 and that therefore a long neck must have been an advantage, and 

 have been liable to be increased ; but it is replied that there were 



