186 
DIFFICULTIES ON THEOKY. 
Chap. VL 
stating the fact in dignified language. He who believes 
in the struggle for existence and in the principle of na¬ 
tural 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 sur¬ 
prise that there should be geese and frigate-birds with 
webbed feet, 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. 
Organs of extreme perfection and complication, — To 
suppose that the eye, with all its inimitable contrivances 
for adjusting the focus to different distances, for ad¬ 
mitting different amounts of light, and for the correc¬ 
tion of spherical and chromatic aberration, could have 
been formed by natural selection, seems, I freely con¬ 
fess, 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 certainly 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 selection, 
though insuperable by our imagination, can hardly be 
considered real. How a nerve comes to be sensitive to 
