282 EECAPITULATION. [Chap. XV. 



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 inexplic- 

 able on the theory of creation. 



As natural selection acts solely by accumulating slight, 

 successive, favourable variations, it can produce no great 

 or sudden modifications ; it can act only by short and 

 slow steps. Hence, the canon of "datura non facit 

 sakum," which every fresh addition to our knowledge 

 tends to confirm, 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 different ways have 

 to be adapted for the same general purpose. Wq 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, should prey on insects on the 

 ground ; that upland geese which rarely or never swim, 

 should 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 each species constantly trying to increase 

 in number, with natural selection always ready to adapt 

 the slowly varying descendants of each to any un- 

 occupied or ill-occupied place in nature, these facts cease 

 to be strange, or might even have been anticipated. 



We can to a certain extent understand how it is that 



