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