I will conclude this chapter by some remarks on an important subject. With
animals such as the giraffe, of which {221} the whole structure is
admirably co-ordinated for certain purposes, it has been supposed that all
the parts must have been simultaneously modified; and it has been argued
that, on the principle of natural selection, this is scarcely possible. But
in thus arguing, it has been tacitly assumed that the variations must have
been abrupt and great. No doubt, if the neck of a ruminant were suddenly to
become greatly elongated, the fore limbs and back would have to be
simultaneously strengthened and modified; but it cannot be denied that an
animal might have its neck, or head, or tongue, or fore-limbs elongated a
very little without any corresponding modification in other parts of the
body; and animals thus slightly modified would, during a dearth, have a
slight advantage, and be enabled to browse on higher twigs, and thus
survive. A few mouthfuls more or less every day would make all the
difference between life and death. By the repetition of the same process,
and by the occasional intercrossing of the survivors, there would be some
progress, slow and fluctuating though it would be, towards the admirably
co-ordinated structure of the giraffe. If the short-faced tumbler-pigeon,
with its small conical beak, globular head, rounded body, short wings, and
small feet--characters which appear all in harmony--had been a natural
species, its whole structure would have been viewed as well fitted for its
life; but in this case we know that inexperienced breeders are urged to
attend to point after point, and not to attempt improving the whole
structure at the same time. Look at the greyhound, that perfect image of
grace, symmetry, and vigour; no natural species can boast of a more
admirably co-ordinated structure, with its tapering head, slim body, deep
chest, tucked-up abdomen, rat-like tail, and long muscular limbs, all
adapted for extreme fleetness, and for running down weak prey. Now, from
what we see of the variability of animals, and from what we know of the
method which different men follow in improving their stock--some chiefly
attending to one point, others to another point, others again correcting
defects by crosses, and so forth--we may feel assured that if we could see
the long line of ancestors of a first-rate greyhound, up to its wild
wolf-like progenitor, we should behold an infinite number of the finest
gr