Whether, during the gradual
development of climbing plants, natural selection has been aided by the
inherited effects of use, I will not pretend to decide; but we know that
certain periodical movements, for instance the so-called sleep of plants,
are governed by habit.
I have now considered enough, perhaps more than enough, of the cases,
selected with care by a skilful naturalist, to prove that natural selection
is incompetent to account for the incipient stages of useful structures;
and I have shown, as I hope, that there is no great difficulty on this
head. A good opportunity has thus been afforded for enlarging a little on
gradations of structure, often associated with strange functions--an
important subject, which was not treated at sufficient length in the former
editions of this work. I will now briefly recapitulate the foregoing
cases.
With the giraffe, the continued preservation of the individuals of some
extinct high-reaching ruminant, which had the longest necks, legs, etc.,
and could browse a little above the average height, and the continued
destruction of those which could not browse so high, would have sufficed
for the production of this remarkable quadruped; but the prolonged use of
all the parts, together with inheritance, will have aided in an important
manner in their co-ordination. With the many insects which imitate various
objects, there is no improbability in the belief that an accidental
resemblance to some common object was in each case the foundation for the
work of natural selection, since perfected through the occasional
preservation of slight variations which made the resemblance at all closer;
and this will have been carried on as long as the insect continued to vary,
and as long as a more and more perfect resemblance led to its escape from
sharp-sighted enemies.
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