g their breeds more quickly than the
small holders on the intermediate narrow, hilly tract; and consequently
the improved mountain or plain breed will soon take the place of the
less improved hill breed; and thus the two breeds, which originally
existed in greater numbers, will come into close contact with each
other, without the interposition of the supplanted, intermediate hill
variety.

To sum up, I believe that species come to be tolerably well-defined
objects, and do not at any one period present an inextricable chaos of
varying and intermediate links: first, because new varieties are very
slowly formed, for variation is a slow process, and natural selection
can do nothing until favourable individual differences or variations
occur, and until a place in the natural polity of the country can
be better filled by some modification of some one or more of its
inhabitants. And such new places will depend on slow changes of climate,
or on the occasional immigration of new inhabitants, and, probably, in
a still more important degree, on some of the old inhabitants becoming
slowly modified, with the new forms thus produced and the old ones
acting and reacting on each other. So that, in any one region and at
any one time, we ought to see only a few species presenting slight
modifications of structure in some degree permanent; and this assuredly
we do see.

Secondly, areas now continuous must often have existed within the recent
period as isolated portions, in which many forms, more especially
among the classes which unite for each birth and wander much, may have
separately been rendered sufficiently distinct to rank as representative
species. In this case, intermediate varieties between the several
representative species and their common parent, must formerly have
existed within each isolated portion of the land, but these links
during the process of natural selection will have been supplanted and
exterminated, so that they will no longer be found in a living state.

Thirdly, when two or more varieties have been formed in different
portions of a strictly continuous area, intermediate varieties will, it
is probable, at first have been formed in the intermediate zones, but
they will generally have had a short duration. For these intermediate
varieties will, from reasons already assigned (namely from what we know
of the actual distribution of closely allied or representative species,
and likewise of acknowledged varieties),