Chap. XIV. RECAPITULATION. 421 



relations on the view that each species was independently 

 created, but are intelligible if each existed fust as a variety. 



As each species tends by its jji:eoinelrical ratio of rei)roduc- 

 tion to increase inordinately in number ; and as the modified 

 descendants of each species will be enabled to increase by so 

 much the more as they become diversified in habits and struct- 

 ure, so as to be enabled to seize on many and widely diflerent 

 jilaces in the economy of Nature, there will be a constant ten- 

 dency in natural selection to preserve the most divergent oft- 

 spriiior of any one species. Hence, during a long-continued 

 course of modification, the slight differences, characteristic of 

 varieties of the same species, tend to be augmented into the 

 greater differences characteristic of the species of the same 

 genus. New and improved varieties will inevitably supplant 

 and exterminate the older, less improved, and inteimediate 

 varieties ; and thus species are rendered to a large extent de- 

 fined and distinct objects. Dominant species belonging to the 

 larger groups within each class t(>nd 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 tlius succeed in increasing in size, for 

 the world would not hold them, the more dominant groups 

 beat tlie less dominant. This tendency in the large groups to 

 go on increasing in size and diverging in character, together 

 with the almost inevitable contingency of much extinction, ex- 

 plains the arrangement of all the forms of life, in groups sub- 

 ordinate to groujis, 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 tlieory of creation. 



As natural selection acts solely by accumulating slight, 

 successive, favorable variations, it can produce no great or sud- 

 den modification ; it can act only by short and slow steps. 

 Hence the canon of " Natura iion facit saltum," which every 

 fresh addition to our knowledge! lends to make truer, is on 

 this theory intelligible. We can sec; why throughout Nature 

 the .same general end is gained by an almost inliiiite diversity 

 of Tneans ; for every peculiarity when once acquired is long 

 inherited, and structures already diversified in many ways 

 have to be adapted for the same general purpose. AVe can, 

 in short, see why Nature is prodigal in variety, though nig- 

 gard in innovation. But why this .should be a law of Nature 

 if each species had been independently created, no man can 

 ex])lain. 



