OF TRANSITIONAL VARIETIES. 163 



will be strongly in favor of the great holders on the mount- 

 ains or on the plains, iiiiproving 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 ex- 

 isted in greater numbers, will come into close contact with 

 each other, without the interposition of the supplanted, in- 

 termediate 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 vari- 

 ation is a slow pi'ocess, and natural selection can do noth- 

 ing until favorable individual differences or variations 

 occur, and until a place in the natural polity of the coun- 

 try can be better filled by some modification of some one 

 or more of its inhabitants. And such new places will de- 

 pend on slow changes of climate, or on the occasional im- 

 migration 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 struc- 

 ture 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 sepa- 

 rately been rendered sufficiently distinct to rank as repre- 

 sentative species. In this case, intermediate varieties be- 

 tween 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 extermin- 

 ated, 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, interme- 

 diate varieties will, it is probable, at first have been formed 

 in the intermediate zones^ but they will generally have had 



