NATURAL SELECTION. 101 



It may metaphorically be said that natural selection is 

 daily and hourly scrutinizing, throughout the world, the 

 slightest variations : rejecting those that are bad, pre- 

 serving and adding up all that are good ; silently and 

 insensibly working, whenever and wherever opportunity 

 offers, at the improvement of each organic being in rela- 

 tion to its organic and inorganic conditions of life. We 

 see nothing of these slow changes in progress, until the 

 hand of Time has marked the lapse of ages, and then so 

 imperfect is our view into long-past geological ages that 

 we see only 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 importance, may thus be acted on. 

 When we see leaf-eating insects green and bark-feeders 

 mottled-gray, the Alpine ptarmigan white in winter, the 

 red-grouse the color of heather, 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 eye-sight 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 natural selection might be 

 effective in giving the proper color to each kind of grouse, 

 and in keeping that color, when once acquired, true and 



K constant. Nor ought we to think that the occasional 

 estruction of an animal of any particular color would 

 roduce little effect : we should remember how essential 



