Page - 183 - in The Origin of Species

TRANSITIONAL VARIETIES 183 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, with- out the interposition of the supplanted, intermediate hill varietv. To sum up, I believe that species come to be tolerably well- defined objects, and do not at any one period present an inex- tricable chaos of varying and intermediate links : first, be- cause 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 un- til a place in the natural polity of the country can be better filled by some modification of some one or more of its inhabit- ants. 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 modifi- cations of structure in some degree permanent; and this as- suredly we do see. Secondly, areas now continuous must often have existed within the recent period as isolated portions, in which many forms, more especially amongst the classes which unite for each birth and wander much, may have separately been ren- dered sufficiently distinct to rank as representative species. In this case, intermediate varieties between the several repre- sentative 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