OBJECTIONS TO THE THEORY OF DESCENT. 319 



WHY WE DO NOT FIND TKAXSITIOXAL FOE3IS. 



Origin of It- ma y be urged that, when several closely- 



Species, allied species inhabit the same territory, we 

 pa ° e ' surely ought to find at the present time many 

 transitional forms. 



p ^ 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 inter- 

 mediate links : first, because new varieties are very slowly 

 formed, for variation is a slow process, and natural selec- 

 tion can do nothing until favorable 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 in- 

 habitants 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 ex- 

 isted 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 com- 

 mon parent must formerly have existed within each 

 isolated portion of the land, but these links during the 



