164 ORGANIC EVOLUTION CONSIDERED 



and independently have ministered to the same func- 

 tion. On the other hand, there would be nothing 

 against the theory of natural selection in the fact 

 that two structures, not homologous, should come by 

 independent variation in two different lines of descent 

 to be adapted to perform the same function. For it 

 belongs to the very essence of the theory of natural 

 selection that a useful function should be secured by 

 favorable variations of whatever structural material 

 may happen to be presented by different organic 

 types. 



" Flying, for instance, is a very useful function, and 

 it has been developed in at least four different lines 

 of descent, namely, the insects, reptiles, birds and 

 mammals. Now if in all, or indeed in any of these 

 four cases, the wings had been developed on the same 

 anatomical pattern, so as not only to present the an- 

 alytical resemblance which it is necessary they should 

 present in order to discharge their common function 

 of flying, but likewise an homologous or structural 

 resemblance, showing that they had been formed on 

 the same anatomical ' plan ' — if such has been the 

 case, I say, the theory of natural selection would cer- 

 tainly be destroyed." 



Here we have the admission that if any two of 

 these wings were homologous it would be fatal to the 

 theory of natural selection. The wings of the ptero- 

 dactyl and bat have been independently evolved, if at 

 all, and yet they are so nearly homologous that they 

 bring the theory quite to the verge of destruction. 

 The only difference is that the pterodactyl has only 

 one finger lengthened for sustaining the membrane, 

 while the bat has four. 



Romanes and others claim that the theory of nat- 

 ural selection will account for any number of anal- 

 ogous organs. This, however, is assuming the great 



