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 believes 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.
_Organs of extreme perfection and complication_. To suppose that the
eye, with all its inimitable contrivances 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 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 light, hardly
concerns us more than how life itself first originated; but I may
remark that several facts make me suspect that any sensitive nerve may
be rendered sensitive to light, and likewise to those coarser
vibrations of the air which produce sound.
In looking for the gradations by which an organ in any species has been
perfected, we ought to look exclusively to its lineal ancestors; but
this is scarcely ever possible, and we are forced in each case to look
to species of the same group, that is to the collateral descendants
from the same original parent-form, in order to see what gradations are
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