ISOLATION 169 



less through ignorance, and that a better acquain- 

 tance with the habits of the animals or plants would 

 show us their uses. Still, making every allowance 

 for this, we cannot suppose that many of the trivial 

 characters which distinguish different species can 

 be of any special use to them. Let anyone examine 

 a series of species, belonging to one genus, of insects 

 or of birds, or any other kind of animal, and let him 

 note the minute differences which divide them 

 some by one character only, some by several and 

 he will, I think, be convinced that most of them 

 cannot be called useful. 



I have already, in the last chapter, given a good 

 many examples of what appear to be useless charac- 

 ters ; but as this is a very important subject, invol- 

 ving large issues, and is strongly contested, I make 

 no apology for dilating a little more on it. I will take 

 the group of petrels (Tubinares), and see what char- 

 acters can be accounted for by selection. I choose 

 this group, because the habits and surrounding con- 

 ditions of sea-birds are so much more simple than 

 those which live on the land, that we can speak 

 more confidently about them. Evidently the long 

 wings and webbed feet are adaptations ; but we do 

 not yet know the use of the tube into which the 

 nostrils are produced ; for the birds hunt by sight. 

 The distinctive characters of the different families 

 are the shape of the sternum and of the bones of the 

 shoulder-girdle ; the position and shape of the nasal- 

 tubes ; the absence or presence of lamellae on the 

 sides of the palate ; and the relative lengths of the 

 first and second feathers of the wing. We cannot, 



