sm.

{223} <Note in original.> Compare feathered heads in very different
birds with spines in Echidna and Hedgehog. <In _Variation under
Domestication_, Ed. ii. vol. II. p. 317, Darwin calls attention to
laced and frizzled breeds occurring in both fowls and pigeons. In
the same way a peculiar form of covering occurs in Echidna and the
hedgehog.>

Plants under very different climate not varying. Digitalis shows
jumps <?> in variation, like Laburnum and Orchis case--in fact hostile
cases. Variability of sexual characters alike in domestic and wild.

Although the amount of variation be exceedingly small in most organic
beings in a state of nature, and probably quite wanting (as far as our
senses serve) in the majority of cases; yet considering how many animals
and plants, taken by mankind from different quarters of the world for
the most diverse purposes, have varied under domestication in every
country and in every age, I think we may safely conclude that all
organic beings with few exceptions, if capable of being domesticated and
bred for long periods, would vary. Domestication seems to resolve itself
into a change from the natural conditions of the species [generally
perhaps including an increase of food]; if this be so, organisms in a
state of nature must _occasionally_, in the course of ages, be exposed
to analogous influences; for geology clearly shows that many places
must, in the course of time, become exposed to the widest range of
climatic and other influences; and if such places be isolated, so that
new and better adapted organic beings cannot freely emigrate, the old
inhabitants will be exposed to new influences, probably far more varied,
than man applies under the form of domestication. Although every species
no doubt will soon breed up to the full number which the country will
support, yet it is easy to conceive that, on an average, some species
may receive an increase of food; for the times of dearth may be short,
yet enough to kill, and recurrent only at long intervals. All such
changes of conditions from geological causes would be exceedingly slow;
what effect the slowness might have we are ignorant; under domestication
it appears that the effects of change of conditions accumulate, and then
break out. Whatever might be the result of these slow geological
changes, we may feel sure, from the means of dissemination common in a
lesser or greater degree to every o