RECAPITULATION 291 



diilerences characteristic of the species of the same genus. 

 New and improved varieties will inevitably supplant and 

 exterminate the older, less improved, and intermediate 

 varieties; and thus species are rendered to a large extent 

 defined and distinct objects. Dominant species belonging 

 to the larger groups within each class tend to give birth 

 to new and dominant forms; so that each large group 

 tends to become still larger, and at the same time more 

 divergent in character. But as all groups cannot thus go 

 on increasing in size, for the world would not hold them, 

 the more dominant groups beat the less dominant. This 

 tendency in the large groups to go on increasing in size 

 and diverging in character, together with the inevitable 

 contingency of much extinction, explains the arrangement 

 of all the forms of life in groups subordinate to groups, 

 all within a few great classes, which has prevailed 

 throughout all time. This grand fact of the group- 

 ing of all organic beings under what is called the 

 Natural System, is utterly inexplicable on the theory 

 of creation. 



Asngiural selection acts solely by accumulating slight,^ 

 successive, favorable variationsT^t caj. produce no great I 

 or sudden modifica tions; it can act only 15y~short and y^^ 

 slow steps. Hence^^ the canon of ^Ifatufa non facit / 

 salturop^^which e'very fresh: addition to^ourllEnowledge j 

 tends to confirm, is^'on "this~tEeofy~Tnteiiigible/ We can-^ 

 see why throughouF nature tEe~""~same general end is 

 gained by an almost infinite diversity of means, for every 

 peculiarity when once acquired is long inherited, and 

 structures already modified in many different ways have 

 to be adapted for the same general purpose. We can, 

 in short, see why nature is prodigal in variety, though 



