The Descent of Man

had been more constant than they are at present,
and had not graduated into each other.
It is however possible, though far from probable,
that the early progenitors of man might
formerly have diverged much in character, until
they became more unlike each other than
any now existing races; but that subsequently,
as suggested by Vogt (22. 'Lectures on Man,'
Eng. translat., 1864, p. 468.), they converged in
character. When man selects the offspring of
two distinct species for the same object, he sometimes
induces a considerable amount of
convergence, as far as general appearance is
concerned. This is the case, as shewn by von
Nathusius (23. 'Die Rassen des Schweines,'
1860, s. 46. 'Vorstudien fur Geschichte,' etc.,
Schweinesschadel, 1864, s. 104. With respect to
cattle, see M. de Quatrefages, 'Unite de l'Espece
Humaine,' 1861, p. 119.), with the improved
breeds of the pig, which are descended from
two distinct species; and in a less marked man-