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On the Origin of Species

Natural Selection; Or The Survival Of The Fittest
Natural Selection -- its power compared with man's selection -- its power on characters of
trifling importance -- its power at all ages and on both sexes -- Sexual Selection -- On the
generality of intercrosses between individuals of the same species -- Circumstances
favourable and unfavourable to the results of Natural Selection, namely, intercrossing,
isolation, number of individuals -- Slow action -- Extinction caused by Natural Selection
-- Divergence of Character, related to the diversity of inhabitants of any small area and to
naturalisation -- Action of Natural Selection, through Divergence of Character and
Extinction, on the descendants from a common parent -- Explains the Grouping of all
organic beings -- Advance in organisation -- Low forms preserved -- Convergence of
character -- Indefinite multiplication of species -- Summary.
How will the struggle for existence, briefly discussed 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 under nature? I think we shall see that it can act most efficiently. Let the
endless number of slight variations and individual differences occurring in our domestic
productions, and, in a lesser degree, in those under nature, be borne in mind; as well as
the strength of the hereditary tendency. Under domestication, it may truly be said that the
whole organisation becomes in some degree plastic. But the variability, which we almost
universally meet with in our domestic productions is not directly produced, as Hooker
and Asa Gray have well remarked, by man; he can neither originate varieties nor prevent
their occurrence; he can only preserve and accumulate such as do occur. Unintentionally
he exposes organic beings to new and changing conditions of life, and variability ensues;
but similar changes of conditions might and do occur under nature. Let it also 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; and consequently what
infinitely varied diversities of structure might be of use to each being under changing
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 occur in the course of many successive
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 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 individual differences and
variations, and the destruction of those which are injurious, I have called Natural
Selection, or the Survival of the Fittest. Variations neither useful nor injurious would not
be affected by natural selection, and would be left either a fluctuating element, as perhaps
we see in certain polymorphic species, or would ultimately become fixed, owing to the
nature of the organism and the nature of the conditions.
Several writers have misapprehended or objected to the term Natural Selection. Some
have even imagined that natural selection induces variability, whereas it implies only the
preservation of such variations as arise and are beneficial to the being under its conditions
 
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