186 DIFFICULTIES ON THEOEY. Chap. VI. 



Creator to cause a being of one type to take the place 

 of one of another type; but this seems to me only 

 restating the fact in dignified language. He who be- 

 lieves in the struggle for existence and in the principle 

 of natural selection, will acknowledge that every organic 

 being is constantly endeavouring to increase in numbers ; 

 and that if any one being vary ever so little, either in 

 habits or structure, and thus gain an advantage over 

 some other inhabitant of the country, it will seize on 

 the place of that inhabitant, however different it may 

 be from its own place. Hence it will cause him no 

 surprise that there should be geese and frigate-birds 

 with webbed feet, either living on the dry land or most 

 rarely alighting on the water ; that there should be 

 long-toed corncrakes living in meadows instead of in 

 swamps ; that there should be woodpeckers where not 

 a tree grows ; that there should be diving thrushes, and 

 petrels with the habits of auks. 



of extreme 'perfection and complication. — 

 To suppose that the eye, with all its inimitable con- 

 trivances for adjusting the focus to different distances, 

 for admitting different amounts of light, and for the 

 correction of spherical and chromatic aberration, could 

 have been formed by natural selection, seems, I freely 

 confess, absurd in the highest possible degree. Yet 

 reason tells me, that if numerous gradations from a 

 perfect and complex eye to one very imperfect and 

 simple, each grade being useful to its possessor, can be 

 shown to exist ; if further, the eye does vary ever so 

 slightly, and the variations be inherited, which is cer- 

 tainly the case ; and if any variation or modification 

 in the organ be ever useful to an animal under changing 

 conditions of life, then the difficulty of believing that 

 a perfect and complex eye could be formed by natural 



