116 EARLY DAYS OF DARWINISM 



a mere change of colour) of an animal must in some wa^ 

 or other affect the ease or difficulty with which it con 

 contrives to maintain its existence. In the struggle fo 

 life which we know to be going on among all species, ; 

 very slight change for the better, such as improve* 

 means of escaping from its natural enemies (which wouL 

 be the effect of an alteration in colour from one differin 

 much to one closely resembling the hue of surroundiii 

 objects), would give that variety a great advantage ove 

 the typical or other forms of the species. Allow th 

 advantage to be continued for a considerable period 

 and the variety becomes not only a race with its varia 

 tions still more strongly imprinted upon it, but the typicg 

 form or varieties having experienced changes not ad 

 vantageous to their life may even become extinct 

 Thus to apply the case, suppose an Algerian desert t 

 become colonised by a few pairs of Crested Lark ; w 

 know that the probability is that of them one or tw 

 pairs would be likely to be of a darker complexion tha] 

 the others, these and such of their offspring as mos 

 resembled them would become more liable to captur 

 by their natural enemies, hawks, carnivorous beasts- 

 etc. ; the lighter coloured ones would enjoy more c 

 less immunity from such attacks ; let the state of thing 

 continue a few hundred years, the dark-coloured in 

 dividuals would be exterminated, the lighter-colourei 

 remain and inhabit the land. 



Again, smaller or shorter-billed varieties woul 

 undergo comparative difficulty in finding food whe: 

 food was not abundant, and had to be picked out fror 

 crevices among stones, these would be in comparative! 

 reduced condition, in the breeding season they wouL 

 not feel their capabilities were such as inclined them t 

 matrimony, the consequences would be in a few hundrei 

 years the longer-billed varieties would be the mos 

 numerous, they would become a race, in a few hundrei 

 years more they would be the sole possessors of the land 

 the shorter-billed fellows dying out of their way unt: 

 that race was extinct. Here are only two cases enume 



