NATURAL SELECTION 



being in relation to its organic and inorganic condi- 

 tions of life. We see nothing of these slow changes in 

 progress, until the hand of time has marked the long 

 lapse of ages, and then so imperfect is our view into 

 long past geological ages, that we only see that the 

 forms of life are now different from what they formerly 



were. 



Although natural selection can act only through and 

 for the good of each being, yet characters and structures, 

 which we are apt to consider as of very trifling import- 

 ance, may thus be acted on. W"hen we see leaf-eating 

 insects green, and bark- feeders mottled -grey ; the 

 alpine ptarmigan white in winter, the red-grouse the 

 colour of heather, and the black-grouse that of peaty 

 earth, we must believe that these tints are of service to 

 these birds and insects in preserving them from danger. 

 Grouse, if not destroyed at some period of their lives, 

 would increase in countless numbers ; they are known 

 to suffer largely from birds of prey ; and hawks are 

 guided by eyesight to their prey — so much so, that on 

 parts of the Continent persons are warned not to keep 

 white pigeons, as being the most liable to destruction. 

 Hence I can see no reason to doubt that natural selec- 

 tion might be most effective in giving the proper colour 

 to each kind of grouse, and in keeping that colour, 

 when once acquired, true and constant. Nor ought we 

 to think that the occasional destruction of an animal of 

 any particular colour would produce little effect : we 

 should remember how essential it is in a flock of white 

 sheep to destroy every lamb with the faintest trace of 

 black. In plants the down on the fruit and the colour 

 of the flesh are considered by botanists as characters of 

 the most trifling importance : yet we hear from an 

 excellent horticulturist, Downing, that in the United 

 States smooth-skinned fruits suffer far more from a 

 beetle, a curculio, than those with down ; that purple 

 plums suffer far more from a certain disease than yellow 

 plums ; whereas another disease attacks yellow-fleshed 

 peaches far more than those with other coloured flesh. 

 If, with all the aids of art, these slight differences make 



