/ 



126 THE ORIGIN OF SPECIES 



Xt-wmT^-TTttrtrtp boric till y be said that natural selection is 

 dix'iTy and hourly scrutinizing, throughout the W()rld, the 

 slightest variations; rejecting those that are bad, preserv- 

 ing and adding up all that are good; silently and insen- 

 sibly working, ivhenever and ivherever 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 



j that the forms of life are now different from what they 



\ formerlv were. 



/^ Inorder that_any great amount of modification_ should 

 be efiec ted in a specieSi_a_yariety 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 be again 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 hy- 

 pothesis accords with and explains the general phenom- 

 — ^a of nature. On the other hand, the ordinary belief 

 that the amount of possible 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 impor- 

 tance, 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 





