Variation and Natural Selection. 89 



siclered at some length because, on the hypothesis of 

 natural selection, they admirably illustrate the results 

 which may be reached through long-continued elimination 

 by enemies. 



Sufficient has now been said to show that this form of 

 elimination is an important factor. We are not at present 

 considering the question how variations arise, or why they 

 should take any particular direction. But granting the 

 fact that variations may and do occur in all parts of the 

 organism, it is clear that, in a group of organisms sur- 

 rounded by enemies, those individuals which varied in the 

 direction of swiftness, cunning, inconspicuousness,* or re- 

 semblance to protected forms, would, other things being 

 equal, stand a better chance of escaping elimination. 



Elimination by competition is, as Darwin well points 

 out, keenest between members of the same group and 

 among individuals of the same species, or between different 

 groups or different species which have, so to speak, similar 

 aims in life. While enemies of various kinds are preying 

 upon weaker animals, and thus causing elimination among 

 them, they are also competing one with another for the 

 prey. While the slower and stupider organisms are suc- 

 cumbing to their captors, and thus leaving more active and 

 cunning animals in possession of the field, the slower and 

 stupider captors, failing to catch their cunning and active 

 prey, are being eliminated by competition. While protec- 

 tive resemblance aids the prey to escape elimination by 

 enemies, a correlative resemblance, called by Mr. Poulton 

 aggressive resemblance, in the captors aids them in stealing 

 upon their prey, and so gives advantage in competition. 

 Thus the hunting spider closely resembles the flies upon 

 which he pounces, even rubbing his head with his fore legs 

 after their innocent fashion. 



* Since the above was -written and sent to press, there has been added, at 

 the Natural History Museum, in the basement hall, a case illustrating the 

 adaptation of external colouring to the conditions of life. All the animals, 

 birds, etc., there grouped were collected in the Egyptian desert, whence also 

 the rocks, stones, and sand on which they are placed were brought. Though 

 somewhat crowded, they exemplify protective resemblance very well 



