§ 1
For every animal one discovers when observing carefully, there must be
ten unseen. This is partly because many animals burrow in the ground or
get in underneath things and into dark corners, being what is called
cryptozoic or elusive. But it is partly because many animals put on
disguise or have in some way acquired a garment of invisibility. This is
very common among animals, and it occurs in many forms and degrees. The
reason why it is so common is because the struggle for existence is
often very keen, and the reasons why the struggle for existence is keen
are four. First, there is the tendency to over-population in many
animals, especially those of low degree. Second, there is the fact that
the scheme of nature involves nutritive chains or successive
incarnations, one animal depending upon another for food, and all in the
long run on plants; thirdly, every vigorous animal is a bit of a
hustler, given to insurgence and sticking out his elbows. There is a
fourth great reason for the struggle for existence, namely, the frequent
changefulness of the physical environment, which forces animals to
answer back or die; but the first three reasons have most to do with the
very common assumption of some sort of disguise. Even when an animal is
in no sense a weakling, it may be very advantageous for it to be
inconspicuous when it is resting or when it is taking care of its young.
Our problem is the evolution of elusiveness, so far at least as that
depends on likeness to surroundings, on protective resemblance to other
objects, and in its highest reaches on true mimicry.