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 organs or parts which in our domesticated
productions have varied, or which still continue to vary,--that is, which fail
to retain their former 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 one another have varied, whilst other parts of the
organisation have remained unchanged; and it might be argued that these same
characters now vary under domestication, or fail to be inherited, from their
lesser antiquity. But variation in a state of nature seems to stand in some
close relation with changed conditions of life, and characters which have
already varied under such conditions would be apt to vary under the still
greater changes consequent on domestication, independently of their greater or
less antiquity.

Fixedness of character, or the strength of inheritance, has often been judged
of by the preponderance of certain characters in the crossed offspring between
distinct races; but prepotency of transmission here comes into play, and this,