184 DIFFICULTIES ON THEORY. Chap. VI. 



seen climbing branches, almost like a creeper ; it often, 

 like a shrike, kills small birds by blows on the head ; 

 and I have many times seen and heard it hammering 

 the seeds of the yew on a branch, and thus breaking 

 them like a nuthatch. In North America the black bear 

 was seen by Hearne swimming for hours with widely 

 open mouth, thus catching, like a whale, insects in the 

 water. Even in so extreme a case as this, if the supply 

 of insects were constant, and if better adapted compe- 

 titors did not already exist in the country, I can see no 

 difficulty in a race of bears being rendered, by natural 

 selection, more and more aquatic in their structure 

 and habits, with larger and larger mouths, till a creature 

 was produced as monstrous as a whale. 



As we sometimes see individuals of a species following 

 habits widely different from those both of their own 

 species and of the other species of the same genus, we 

 might expect, on my theory, that such individuals 

 would occasionally have given rise to new species, having 

 anomalous habits, and with their structure either slightly 

 or considerably modified from that of their proper type. 

 And such instances do occur in nature. Can a more 

 striking instance of adaptation be given than that of a 

 woodpecker for climbing trees and for seizing insects in 

 the chinks of the bark ? Yet in North America there 

 are woodpeckers which feed largely on fruit, and others 

 with elongated wings which chase insects on the wing ; 

 and on the plains of La Plata, where not a tree grows, 

 there is a woodpecker, which in every essential part of its 

 organisation, even in its colouring, in the harsh tone of 

 its voice, and undulatory flight, told me plainly of its 

 close blood-relationship to our common species ; yet it 

 is a woodpecker which never climbs a tree ! 



Petrels are the most aerial and oceanic of birds, yet 

 in the quiet Sounds of Tierra del Fuego, the Puffinuria 



