Chap. XIV. RECAPITULATION. 471 



forms ; so that eacli large group tends to become still 

 larger, and at the same time more divergent in character. 

 But as all groups cannot thus succeed in increasing in 

 size, for the world would not hold them, the more domi- 

 nant groups beat the less dominant. This tendency 

 in the large groups to go on increasing in size and 

 diverging in character, together with the almost in- 

 evitable contingency of much extinction, explains the 

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

 ordinate to groups, all within a few great classes, which 

 we now see everywhere around us, and which has pre- 

 vailed throughout all time. This grand fact of the 

 grouping of all organic beings seems to me utterly 

 inexplicable on the theory of creation. 



As natural selection acts solely by accumulating 

 slight, successive, favourable variations, it can produce 

 no great or sudden modification ; it can act only by very 

 short and slow steps. Hence the canon of " Natura non 

 facit saltum," winch every fresh addition to our know- 

 ledge tends to make more strictly correct, is on this 

 theory simply intelligible. We can plainly see why 

 nature is prodigal in variety, though niggard in innova- 

 tion. 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 woodpecker, should have been created to 

 prey on insects on the ground ; that upland geese, 

 which never or rarely swim, should have been created 

 with webbed feet ; that a thrush should have been 

 created to dive and feed on sub-aquatic insects; and 

 that a petrel should have been created witli habits and 

 structure fitting it for the life of an auk or grebe ! and 

 so on in endless other cases. But on the view of each 



