02 ILLUSTRATIONS OF THE ACTION OF Chap. IV. 



Iv. Iloroii has described how one pied peacock was eminently 

 attractive to all his hen-birds. I cannot here enter on the ne- 

 cessary details ; but if man can in a short time jjive elegant 

 carriage and beauty to his bantams according to liis standard 

 of beauty, I can see no good reason to doubt that female 

 birds, by selecting, during thousands of generations, the most 

 melodious or beautiful males, according to their standard of 

 beauty, might jiroduce 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 be explained 

 through the action of sexual selection on variations occurring 

 at diiierent ages, and being transmitted to the males alone or 

 to both sexes at a corresponding age ; 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 diller in 

 structure, color, or ornament, such differences have been main- 

 ly caused by sexual selection ; that is, by individual males hav- 

 ing had, in successive generations, some slight advantage over 

 other males, in their weapons, means of defence, or charms ; 

 and having transmitted these advantages to their male off- 

 spring. Yet, I would not Avish to attribute all such sexual dif- 

 ferences to this agency : for we see peculiarities arising and 

 becoming attached to the male sex in our domestic animals (as 

 the greater development of the Avattle in male carrier-pigeons, 

 horn-like protuberances in certain fowls, etc.), Avhich are in no 

 way useful. We see analogous cases under Nature — for in- 

 stance, the tuft of hair on the breast of the turkej'-cock, Avliich 

 cannot be useful, and can hardly be ornamental ; indeed, had 

 the tuft appeared under domestication, it would have been 

 called a monstrosity. 



Illustratio7is of the Action of Natural Selection, or the Sur- 

 vival of the Fittest. 



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

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

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

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

 some by (leetness ; and let us suppose that tlie fleetest prey, 

 a deer for instance, had from any change in the country in- 

 creased in numbers, or that other prey had decreased in num- 

 bers, during that season of the year when the wolf was hardest 



