ompetitors, were not in the course of time in some manner
modified. It should also be remembered that many characters lie latent in
all organic beings ready to be evolved under fitting conditions; and in
breeds modified within recent times the tendency to reversion is
particularly strong. But the antiquity of various breeds clearly proves
that they remain nearly constant as long as their conditions of life remain
the same.

It has been boldly maintained by some authors that the amount of variation
to which our domestic productions are liable is strictly limited; but this
is an assertion resting on little evidence. Whether or not the amount in
any particular direction is fixed, the tendency to general variability
seems unlimited. Cattle, sheep, and pigs have been domesticated and have
varied from the remotest period, as shown by the researches of Ruetimeyer
and others, yet these animals have, within quite recent times, been
improved in an unparalleled degree; and this implies continued variability
of structure. Wheat, as we know from the remains found in the Swiss
lake-habitations, is one of the most anciently cultivated plants, yet at
the present day new and better varieties occasionally arise. It may be that
an ox will never be produced of larger size or finer proportions than our
present animals, or a race-horse fleeter than Eclipse, or a gooseberry
larger than the London variety; but he would be a bold man who would assert
that the extreme limit in these respects has been finally attained. With
flowers and fruit it has repeatedly been asserted that perfection has been
reached, but the standard has soon been excelled. A breed of pigeons may
never be produced with a beak shorter than that of the present short-faced
tumbler, or with one longer than that of the English carrier, for these
birds have weak constitutions and are bad breeders; but the shortness and
length of the beak are the points which have been steadily improved during
at least the last 150 years; and some of the best judges deny that the goal
has yet been reached. We may, also, reasonably suspect, from what {417} we
see in natural species of the variability of extremely modified parts, that
any structure, after remaining constant during a long series of
generations, would, under new and changed conditions of life, recommence
its course of variability, and might again be acted on by selection.
Nevertheless, as Mr. Wallace[930] has recently remarked with much