106 REDUCTION OF VARIABILITY. 



ness of some organ, some part, there is not much to be said 

 against this reasoning. But it rather implies, that any quality 

 for which we see that a species is now pure, must have, or at 

 least must have had, its use, or must have been correlated with 

 something useful. And this consideration has led a great num- 

 ber of authors always to look for the usefulness of every trifle, 

 they could discover about plants or animals. 



If a spot on the wing of a butterfly makes it a little less con- 

 spicuous, it is the intention of this spot to bring about this 

 inconspicuousness. If, however, the spot makes the animal 

 rather more visible, then the spot is there to make the animal 

 conspicuous. If we observe the stripes of a zebra, we think 

 these stripes make the animal invisible. If next we observe 

 that our zebra cannot keep its switching tail from moving con- 

 tinually, and giving him away, we decide that this nervous 

 trick is an adaptation to a fly-infested country. A bird looks 

 like another bird to which it is not related, and forthwith we 

 declare that the one must imitate the other. Dewar and Finn 

 give a whole list of instances in which two birds resemble 

 each other very much more closely than the classical examples 

 of imitation, but in which the two members of such a pair in- 

 habit different continents and never had any relation to each 

 other. Almost any bit of coloration of any organism can be 

 said to be useful in some way, if the good iaith of the natural- 

 ist is only sustained by a competent imagination. 



William Ritter has repeatedly pointed out the sterility of 

 this hunt for the meaning of everything. If we see that the oc- 

 ciput of a bird is black, why, it is black, because it is not blue 

 or pink, if it were not black it would have some other colour, 

 colour it must have. 



It is very apparent, that if two birds can coexist in one en 

 vironment and be so nearly alike in habits and nesting-place as 

 European the blue tit and the great tit, we cannot invoke the 

 usefulness of the sky-blue markings of the smaller bird as the 

 cause of the fact, that all the individuals are pure for the com- 

 bination of genes which results in this colour, any more than 



