bull, the greater length of horn, though appearing late in life, is
clearly due to the male element.
Having alluded to the subject of reversion, I may here refer to a
statement often made by naturalists namely, that our domestic
varieties, when run wild, gradually but certainly revert in character
to their aboriginal stocks. Hence it has been argued that no deductions
can be drawn from domestic races to species in a state of nature. I
have in vain endeavoured to discover on what decisive facts the above
statement has so often and so boldly been made. There would be great
difficulty in proving its truth: we may safely conclude that very many
of the most strongly-marked domestic varieties could not possibly live
in a wild state. In many cases we do not know what the aboriginal stock
was, and so could not tell whether or not nearly perfect reversion had
ensued. It would be quite necessary, in order to prevent the effects of
intercrossing, that only a
single variety should be turned loose in its new home. Nevertheless, as
our varieties certainly do occasionally revert in some of their
characters to ancestral forms, it seems to me not improbable, that if
we could succeed in naturalising, or were to cultivate, during many
generations, the several races, for instance, of the cabbage, in very
poor soil (in which case, however, some effect would have to be
attributed to the direct action of the poor soil), that they would to a
large extent, or even wholly, revert to the wild aboriginal stock.
Whether or not the experiment would succeed, is not of great importance
for our line of argument; for by the experiment itself the conditions
of life are changed. If it could be shown that our domestic varieties
manifested a strong tendency to reversion, that is, to lose their
acquired characters, whilst kept under unchanged conditions, and whilst
kept in a considerable body, so that free intercrossing might check, by
blending together, any slight deviations of structure, in such case, I
grant that we could deduce nothing from domestic varieties in regard to
species. But there is not a shadow of evidence in favour of this view:
to assert that we could not breed our cart and race-horses, long and
short-horned cattle, and poultry of various breeds, and esculent
vegetables, for an almost infinite number of generations, would be
opposed to all experience. I may add, that when under nature the
conditions of life do change, variations and reversions of character
probably do occur; but natural selection, as will hereafter be
explained, will determine how far the new characters thus arising shall
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