ary wing-feathers, in the relative
length of the hind {223} toe, or in habits of life, as in roosting and
building in trees. But the above objection shows how completely the
principle of selection has been misunderstood. It is not likely that
characters selected by the caprice of man should resemble differences
preserved under natural conditions, either from being of direct service to
each species, or from standing in correlation with other modified and
serviceable structures. Until man selects birds differing in the relative
length of the wing-feathers or toes, &c., no sensible change in these parts
should be expected. Nor could man do anything unless these parts happened
to vary under domestication: I do not positively assert that this is the
case, although I have seen traces of such variability in the wing-feathers,
and certainly in the tail-feathers. It would be a strange fact if the
relative length of the hind toe should never vary, seeing how variable the
foot is both in size and in the number of the scutellae. With respect to the
domestic races not roosting or building in trees, it is obvious that
fanciers would never attend to or select such changes in habits; but we
have seen that the pigeons in Egypt, which do not for some reason like
settling on the low mud hovels of the natives, are led, apparently by
compulsion, to perch in crowds on the trees. We may even affirm that, if
our domestic races had become greatly modified in any of the above
specified respects, and it could be shown that fanciers had never attended
to such points, or that they did not stand in correlation with other
selected characters, the fact, on the principles advocated in this chapter,
would have offered a serious difficulty.

Let us briefly sum up the last two chapters on the pigeon. We may conclude
with confidence that all the domestic races, notwithstanding their great
amount of difference, are descended from the _Columba livia_, including
under this name certain wild races. But the differences between these
latter forms throw no light whatever on the characters which distinguish
the domestic races. In each breed or sub-breed the individual birds are
more variable than birds in a state of nature; and occasionally they vary
in a sudden and strongly-marked manner. This plasticity of organisation
apparently results from changed conditions of life. Disuse has reduced
certain parts of the body. Correlation of growth so ties the organisation
t