tain varieties
retain and transmit through successive bud-generations their newly-acquired
characters more truly than others. In none of these, nor in the following
cases, does there appear to be any relation between the force with which a
character is transmissible and the length of time during which it has
already been transmitted. Some varieties, such as white and yellow
hyacinths and white sweet-peas, transmit their colours more faithfully than
do the varieties which have retained their natural colour. In the Irish
family, mentioned in the twelfth chapter, the peculiar tortoiseshell-like
colouring of the eyes was transmitted far more faithfully than any ordinary
colour. Ancon and Mauchamp sheep and niata cattle, which are all
comparatively modern breeds, exhibit remarkably strong powers of
inheritance. Many similar cases could be adduced.

As all domesticated animals and cultivated plants have varied, and yet are
descended from aboriginally wild forms, which no doubt had retained the
same character from an immensely remote epoch, we see that scarcely any
degree of antiquity ensures a character being transmitted perfectly true.
In this case, however, it may be said that changed conditions of life
induce certain modifications, and not that the power of inheritance fails;
but in every case of failure, some cause, either internal or external, must
interfere. It will generally be found that the parts in our domesticated
productions which have varied, or which still continue to vary,--that is,
which fail to retain their primordial state,--are the same with the parts
which differ in the natural species of the same genus. As, on the theory of
descent with modification, the species of the same genus have been modified
since they branched off from a common progenitor, it follows that the
characters by which they differ from each other have varied whilst other
parts of the organisation have remained unchanged; and it might be argued
that {64} these same characters now vary under domestication, or fail to be
inherited, owing to their lesser antiquity. But we must believe structures,
which have already varied, would be more liable to go on varying, rather
than structures which during an immense lapse of time have remained
unaltered; and this variation is probably the result of certain relations
between the conditions of life and the organisation, quite independently of
the greater or less antiquity of each particular character.