it, and in this way CREATES what is new. EVERYTHING in organisms depends
on adaptation; that is to say, everything must be admitted through the
narrow door of selection, otherwise it can take no part in the building up
of the whole. But, it is asked, what of the direct effect of external
conditions, temperature, nutrition, climate and the like? Undoubtedly
these can give rise to variations, but they too must pass through the door
of selection, and if they cannot do this they are rejected, eliminated from
the constitution of the species.

It may, perhaps, be objected that such external influences are often of a
compelling power, and that every animal MUST submit to them, and that thus
selection has no choice and can neither select nor reject. There may be
such cases; let us assume for instance that the effect of the cold of the
Arctic regions was to make all the mammals become black; the result would
be that they would all be eliminated by selection, and that no mammals
would be able to live there at all. But in most cases a certain percentage
of animals resists these strong influences, and thus selection secures a
foothold on which to work, eliminating the unfavourable variation, and
establishing a useful colouring, consistent with what is required for the
maintenance of the species.

Everything depends upon adaptation! We have spoken much of adaptation in
colouring, in connection with the examples brought into prominence by
Darwin, because these are conspicuous, easily verified, and at the same
time convincing for the theory of selection. But is it only desert and
polar animals whose colouring is determined through adaptation? Or the
leaf-butterflies, and the mimetic species, or the terrifying markings, and
"warning-colours" and a thousand other kinds of sympathetic colouring? It
is, indeed, never the colouring alone which makes up the adaptation; the
structure of the animal plays a part, often a very essential part, in the