in the circumstances in which it is placed, that creature will be fitter
than the others which have not that variation. And so the former will
survive, and as they multiply, their descendants will inherit the
peculiarity. Thus, in the course of countless generations, change will
succeed change, till creatures of quite a complex structure and
specialized form have arisen. As the circumstances of life are always
infinitely various, the developments take place in many different
directions; some fit the creature for life in deep seas, some for flying
in the air, some for living in holes and crevices, some for catching
prey by swift pursuit, others for catching it by artful contrivance, and
so forth. Many changes will also arise from protective necessity: if an
insect happens to be like a dead leaf, it will escape the notice of
birds which would snap up a conspicuously coloured one; and so the
dull-coloured will survive and perpetuate his kind, while the others are
destroyed. On the other hand, beauty in colour and form may have its
use. This is chiefly exhibited in the preference which the females of a
species show for the adorned and showy males.


[Footnote 1: Not really of course "by chance," but simply owing to such
circumstances as cannot be accounted for by any direct antecedents.]

Supposing an organism developed so far as to be a bird, but only with
dull or ugly feathers. By accident one male bird, say, gets a few
bright-coloured feathers on his head. Here his appearance will attract
birds of the other sex; and then by the law of heredity, his offspring
are sure to repeat the coloured feathers, till at last a regularly
bright-crested species-arises. In this way _natural variability_, acted
on by the necessities of _environment_ (which cause the _survival of the
fittest_ specimens) and the principle of _heredity_, viz., that the