NATURAL SELECTION. 73 



useful to him. Under nature, the slightest differences of 

 structure or constitution may well turn the nicely balanced 

 scale in the struggle for life, and so be preserved. How 

 fleeting are the wishes and efforts of man ! How short his 

 time, and consequently how poor will be his results, com- 

 pared with those accumulated by Nature during whole 

 geological periods ! Can we wonder, then, that Nature's 

 productions should be far " truer " in character than man's 

 productions ; that they should be infinitely better adapted 

 to the most complex conditions of life, and should plainly 

 bear the stamp of far higher workmanship ? 



It may metaphorically be said that natural selection is 

 daily and hourly scrutinizing, throughout the world, the 

 slightest variations ; rejecting those that are bad, preserv- 

 ing and adding up all that are good ; silently and insensibly 

 working, whenever and wherever opportunity offers, at the 

 improvement of each organic being in relation 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. 



In order that any great amount of modification should be 

 effected in a species, a variety, when once formed, must 

 again, perhaps after a long interval of time, vary or pre- 

 sent individual differences of the same favorable nature as 

 before ; and these must again be preserved, and so onward, 

 step by step. Seeing that individual differences of the 

 same kind perpetually recur, this can hardly be considered 

 as an unwarrantable assumption. But whether it is true, 

 we can judge only by seeing how far the hypothesis accords 

 with and explains the general phenomena of nature. On 

 the other hand, the ordinary belief that the amount of pos- 

 sible variation is a strictly limited quantity, is likewise a 

 simple assumption. 



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 jbhei r lives, would increase ill 



