Science is just now passing through a phase of acute
criticism--as the reader will have realised by this time--and
many of the positions confidently adopted in the earlier
constructive stage are challenged. This applies to the protective
colours, warning colours, mimicry, etc., of insects. Probably
some of the affirmations of the older generation of evolutionists
were too rigid and extensive; and probably the denials of the new
generation are equally exaggerated. When all sound criticism has
been met, there remains a vast amount of protective colouring,
shaping, and marking in the insect world of which natural
selection gives us the one plausible explanation. But the
doctrine of natural selection does not mean that every feature of
an animal shall have a certain utility. It will destroy animals
with injurious variations and favour animals with useful
variations; but there may be a large amount of variation,
especially in colour, to which it is quite indifferent. In this
way much colour-marking may develop, either from ordinary
embryonic variations or (as experiment on butterflies shows) from
the direct influence of surroundings which has no vital
significance.
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