78 ILLUSTRATIONS OF THE ACTION 



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 generations, the most 

 melodious or beautiful males, according to their stand- 

 ard 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, color, or ornament, such differences have 

 been mainly caused by sexual selection: that is, by individ- 

 ual males having had, in successive generations, some slight 

 advantage over other males, in their weapons, means of de- 

 fence, 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 augmented 

 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 domestica- 

 tion it would have been called a monstrosity. 



ILLUSTRATIONS OF THE ACTION OF NATURAL SELECTION, OR 

 THE SURVIVAL 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 ima- 

 ginary illustrations. 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 numbers, 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 have the 

 best chance of surviving, and so being preserved or selected, 

 provided always that they retain strength to master their 



