' THE ORIGIN OP SPECIES ' 97 



fairly be said to struggle with one another for light and 

 air ; and since mistletoe seeds are disseminated by birds 

 and dropped by them in the angles of branches, the 

 mistletoe may also be said to compete with other berry- 

 bearing bushes, like cornel and hawthorn, for the minis- 

 trations of the fruit-eating birds. The struggle is 

 fierce between allied kinds, and fiercest of all between 

 individual members of the same species. 



Owing to this constant struggle, variations, however 

 slight, and from whatever cause arising, if in any degree 

 profitable to the individual which presents them, will 

 tend to the preservation of the particular organism, and, 

 being on the average inherited by its offspring, will 

 similarly tend to increase and multiply in the world at 

 large. This is the principle of natural selection or sur- 

 vival of the fittest the great principle which Darwin 

 and Wallace added to the evolutionism of Lamarck and 

 his successors. 



Let us take a single concrete example. In the 

 desert, with its monotonous sandy colouring, a black 

 insect or a white insect, still more a red insect or a blue 

 insect, would be immediately detected and promptly de- 

 voured by its natural enemies, the birds and lizards. 

 But any greyish or yellowkh insects would be less likely 

 to attract attention at first sight, and would be over- 

 looked as long as there were any more conspicuous in- 

 dividuals of their own kind about for the birds and 

 lizards to feed on at their leisure. Hence, in a very 

 short time, the desert would be depopulated of all but 

 the greyest and yellowest insects ; and among these the 

 birds would pick out those which differed most markedly 

 in hue or shade from the sand around them. But those 



