192 



FOOT-NOTES TO EVOLUTION. 



As Professor Bergen has well said, " It is important 

 that we should understand that none of the kinds of 



evidence in favour of evolution loses so 



Cumulative u u u • .. j 1 i, 



much by being represented only by 



evidence. . , , 



scattered instances as the argument from 



distribution." And, conversely, no argument is more 

 conclusive when all the known facts are brought into 

 consideration together. The universal fact of the muta- 

 bility of species can be really understood or appreciated 

 only by him who has seen with his own eyes the changes 

 in multitudes of species. To the ordinary observer the 

 species seem constant, just as the face of a cliff seems 

 constant. To the student of Nature, mutability is 

 everywhere. Just as the wind and rain and frost quietly 

 but surely change the face of a cliff, so do other forces 

 of Nature as quietly but as surely change the face of a 

 species. 



It was this phase of the subject, the relation of spe- 

 cies to geography, which first attracted the attention 

 both of Darwin and Wallace. Both these observers 

 noticed that island life is neither strictly like nor unlike 

 the life of the nearest land, and that the degree of 

 difference differs with the degree of isolation. Both 

 were led from this fact to the theory of derivation, and 

 to lay the greatest stress on the progressive modifica- 

 tion resulting from the struggle for existence. 



In the voyage of the Beagle Darwin was brought 



in contact with the singular fauna of the Galapagos 



Islands, that cluster of volcanic rocks 

 The fauna of the ^^^j^-^j^ jj^^ j^ ^^^ ^ ^^^ ^^^^^ ^j^ ^^^_ 



Galapagos. , , ., , , ^ t^ , 



dred miles west of the coasts of Ecuador 



and Peru. The sea birds of these islands are essentially 



the same as those of the coast of Peru. So with most 



of the fishes. We can see how this might well be, for 



both sea birds and fishes can readily pass from the 



