CHAP. IV.] NATURAL SELECTION. 65 



play with the most elaborate care, and show off in the best 

 manner, their gorgeous plumage ; they likewise perform strange 

 antics before the females, which, standing by as spectators, at 

 last choose the most attractive partner. Those who have closely 

 attended to birds in confinement well know that they often take in- 

 dividual preferences and dislikes : thus Sir R. Heron has described 

 how a pied peacock was eminently attractive to all his hen birds. 

 I cannot here enter on the necessary details ; but if man can in 

 a short time give beauty and an elegant carriage to his bantams, 

 according to his standard of beauty, I can see no good reason to 

 doubt that female birds, by selecting, during thousands of genera- 

 tions, the most melodious or beautiful males, according to their 

 standard of beauty, might produce a marked effect. Some well- 

 known laws, with respect to the plumage of male and female 

 birds, in comparison with the plumage of the young, can partly 

 be explained through the action of sexual selection on variations 

 occurring at different ages, and transmitted to the males alone or 

 to both sexes at corresponding ages ; but I have not space here to 

 enter on this subject. 



Thus it is, as I believe, that when the males and females of 

 any animal have the same general habits of life, but differ in 

 structure, colour, or ornament, such differences have been mainly 

 caused by sexual selection : that is, by individual males having 

 had, in successive generations, some slight advantage over other 

 males, in their weapons, means of defence, or charms, which they 

 have transmitted to their male offspring alone. Yet, I would not 

 wish to attribute all sexual differences to this agency : for we see 

 in our domestic animals peculiarities arising and becoming 

 attached to the male sex, which apparently have not been aug- 

 mented through selection by man. The tuft of hair on the breast 

 of the wild turkey-cock cannot be of any use, and it is doubtful 

 whether it can be ornamental in the eyes of the female bird ; 

 indeed, had the tuft appeared under domestication, it would have 

 been called a monstrosity. 



Illustrations of tJie Action of Natural Selection, or the Survival 

 of the Fittest. 



In order to make it clear how, as I believe, natural selection 

 acts, I must beg permission to give one or two imaginary illustra- 

 tions. Let us take the case of a wolf, which preys on various 

 animals, securing some by craft, some by strength, and some by 

 fleetness ; and let us suppose that the fleetest prey, a deer for 

 instance, had from any change in the country increased in num- 

 bers, or that other prey had decreased in numbers, during that 

 season of the year when the wolf was hardest pressed for food. 

 Under such circumstances the swiftest and.slimmest wolves would 



