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03/23/10(Tue)15:44:46 No.209323XXX File1269373486.jpg-(24
KB, 303x400, darwin.jpg)
How will the struggle for
existence, discussed too briefly in the last chapter, act in regard to
variation? Can the principle of selection, which we have seen is so
potent in the hands of man, apply in nature? I think we shall see that
it can act most effectually. Let it be borne in mind in what an endless
number of strange peculiarities our domestic productions, and, in a
lesser degree, those under nature, vary; and how strong the hereditary
tendency is. Under domestication, it may be truly said that the, whole
organisation becomes in some degree plastic. Let it be borne in mind how
infinitely complex and close-fitting are the mutual relations of all
organic beings to each other and to their physical conditions of life.
Can it, then, be thought improbable, seeing that variations useful to
man have undoubtedly occurred, that other variations useful in some way
to each being in the great and complex battle of life, should sometimes
occur in the course of thousands of generations? If such do occur, can
we doubt (remembering that many more individuals are born than can
possibly survive) that individuals having any advantage, however slight,
over others, would have the best chance of surviving and of procreating
their kind? On the other hand, we may feel sure that any variation in
the least degree injurious would be rigidly destroyed. This preservation
of favourable variations and the rejection of injurious variations, I
call Natural Selection. Variations neither useful nor injurious would
not be affected by natural selection, and would be left a fluctuating
element, as perhaps we see in the species called polymorphic. |