98 CHARLES DARWIN 



which happened to vary most in the direction of a sandy 

 or spotty colour would be most likely to survive, and to 

 become the parents of future generations. Thus, in the 

 course of long ages, all the insects which inhabit deserts 

 have become sand-coloured ; because the least sandy 

 were perpetually picked out for destruction by their 

 ever-watchful fees, while the most sandy escaped and 

 multiplied and replenished the earth with their own likes. 



Conversely, the birds and the lizards again would 

 probably begin by being black, and white, and blue, and 

 green, like most other birds and lizards in the world 

 generally. But the insect would have ample warning 

 of the near approach of such conspicuous self-advertising 

 enemies, and would avoid them accordingly whenever 

 they appeared within range of his limited vision, either 

 by lying close, or by shamming death, or by retreating 

 precipitately to holes and crannies. Therefore, whatever 

 individual birds or lizards happened to vary most in the 

 direction of grey or sand-colour, and so to creep unob- 

 served upon the unguarded insects, would succeed best 

 on the average in catching beetles or desert grasshoppers. 

 Hence, by the slow dying out of the more highly 

 coloured and distinctive insect-eaters, before the severe 

 competition of the greyest and sandiest, all the birds and 

 lizards of the desert have become at last as absolutely 

 sand-coloured as the insects themselves. Only the greyest 

 insect could escape the bird ; only the greyest bird, en 

 revanche, could surprise and devour the unwary insect. 



Sir Charles Lyell and the elder De Candolle had 

 already seen the great importance of the struggle for 

 existence in the organic world, but neither of them had 

 observed the magnificent corollary of natural selection, 



