UECAPrrULATION. 487 



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 dis- 

 tinct 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 extinc- 

 tion, 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 grouping of all organic beings under what is called 

 the Natural System, is utterly inexplicable on the theory 

 of creation. 



As natural selection acts solely by accumulating slight, 

 successive, favorable variations, it can produce no great or 

 sudden modifications; it can act only by short and slow 

 steps. Hence, the canon of ^'Natura non facit saltum,^' 

 which every fresh addition to our knowledge tends to con- 

 firm, is on this theory intelligible. We can see why 

 throughout nature the 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 dilferent ways have to be adapted 

 for the same general purpose. We can, in short, see why 

 nature is prodigal in variety, though niggard in innovation. 

 But why this should be a law of nature if each species has 

 been independently created no man can explain. 



Many other facts are, as it seems to me, explicable on 

 this theory. How strange it is that a bird, under the form 

 of a woodpecker, shoukl prey on insects on the ground; 

 that upland geese, which rarely or never swim, would 

 possess webbed feet; that a thrush-like bird should dive 

 and feed on sub-aquatic insects; and that a petrel should 

 have the habits and structure fitting it for the life of an 

 auk! and so in endless other cases. But on the view of 

 eacli species constantly trying to increase in number, with 



