The Descent of Man

VARIABILITY OF BIRDS, AND ESPECIA-
LLY OF THEIR SECONDARY SEXUAL CHA-
RACTERS.
Variability and inheritance are the foundations
for the work of selection. That domesticated
birds have varied greatly, their variations being
inherited, is certain. That birds in a state of nature
have been modified into distinct races is
now universally admitted. (33. According to
Dr. Blasius ('Ibis,' vol. ii. 1860, p. 297), there are
425 indubitable species of birds which breed in
Europe, besides sixty forms, which are frequently
regarded as distinct species. Of the latter,
Blasius thinks that only ten are really doubtful,
and that the other fifty ought to be united with
their nearest allies; but this shews that there
must be a considerable amount of variation
with some of our European birds. It is also an
unsettled point with naturalists, whether several
North American birds ought to be ranked as
specifically distinct from the corresponding
European species. So again many North Ameri-