116 EARLY DAYS OF DARWINISM 



a mere change of colour) of an animal must in some way 

 or other affect the ease or difficulty with which it con- 

 contrives to maintain its existence. In the struggle for 

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

 very slight change for the better, such as improved 

 means of escaping from its natural enemies (which would 

 be the effect of an alteration in colour from one differing 

 much to one closely resembhng the hue of surrounding 

 objects), would give that variety a great advantage over 

 the typical or other forms of the species. Allow the 

 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 typical 

 form or varieties having experienced changes not ad- 

 vantageous to their hfe may even become extinct. 

 Thus to apply the case, suppose an Algerian desert to 

 become colonised by a few pairs of Crested Lark ; we 

 know that the probabihty is that of them one or two 

 pairs would be likely to be of a darker complexion than 

 the others, these and such of their offspring as most 

 resembled them would become more liable to capture 

 by their natural enemies, hawks, carnivorous beasts, 

 etc. ; the lighter coloured ones would enjoy more or 

 less immunity from such attacks ; let the state of things 

 continue a few hundred years, the dark-coloured in- 

 dividuals would be exterminated, the lighter-coloured 

 remain and inhabit the land. 



Again, smaller or shorter-billed varieties would 

 undergo comparative difficulty in finding food when 

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

 crevices among stones, these would be in comparatively 

 reduced condition, in the breeding season they would 

 not feel their capabilities were such as inclined them to 

 matrimony, the consequences would be in a few hundred 

 years the longer-biUed varieties would be the most 

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

 years more they would be the sole possessors of the land, 

 the shorter-biUed fellows dying out of their way until 

 that race was extinct. Here are only two cases enume- 



