But this will
not seem so surprising if we keep in mind the facts set forth in our
earlier chapters--the rapid multiplication, the severe struggle for
existence, and the constant variability of these and all other
organisms. And, further, we must remember that these delicate
adjustments are the result of a process which has been going on for
millions of years, and that we now see the small percentage of successes
among the myriads of failures. From the very first appearance of insects
and their various kinds of enemies the need of protection arose, and was
usually most easily met by modifications of colour. Hence, we may be
sure that the earliest leaf-eating insects acquired a green colour as
one of the necessities of their existence; and, as the species became
modified and specialised, those feeding on particular species of plants
would rapidly acquire the peculiar tints and markings best adapted to
conceal them upon those plants. Then, every little variation that, once
in a hundred years perhaps, led to the preservation of some larva which
was thereby rather better concealed than its fellows, would form the
starting-point of a further development, leading ultimately to that
perfection of imitation in details which now astonishes us.
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