IIO THE MEANING OF EVOLUTION 



taken many generations, and is very slow, but is none 

 the less sure in the end. In most cases the animal is 

 probably entirely unconscious of this point in its 

 favor, and usually it does nothing to assist the decep- 

 tion. The result is none the less effective because the 

 animals themselves are unconscious of the process. 

 The cabbage worm is green in color like the cabbage. 

 This does not mean that it got green by eating cab- 

 bage or by longing for greennesses. Through long 

 years the enemies of the cabbage worm have been 

 picking it off the plants on which it fed. This does 

 not imply that cabbages as we know them are very 

 old, but cabbage worms doubtless ate the leaves of the 

 sea-kale long before man had cultivated it into cab- 

 bage. During all these years the enemies of the cater- 

 pillars, generally in the shape of birds, have been as- 

 siduously gathering them up. 



When we see how much the various members of 

 the same human family may differ in complexion, how 

 much the various pigs in the same litter may differ 

 in size and in coloration, it is easy to understand that 

 among these caterpillars which have eaten the cabbage 

 there must have been considerable color variations. I 

 do not imagine for a moment that the birds had any 

 preference for any particular color in their cabbage 

 worms. They took every caterpillar they saw, but 

 they naturally first saw those that were least like the 



