SEXUAL SELECTION. 83 



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

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

 difEer in structure, color, or ornament, such difEerences 

 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 defense, 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 

 domestication it would have been called a monstrosity. 



ILLUSTRATIONS OF THE ACTION" OF NATUBAL 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 imagi- 

 nary 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 

 iu 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 be preserved or 

 selected, provided always that they retained strength to 

 master their prey at this or some other period of the year, 

 when they were compelled to prey on other animals. I can 

 see no more reason to doubt that this would be the result, 

 than that man should be able to improve the fleetness of his 

 greyhounds by careful and methodical selection, or by that 

 kind of unconscious selection which follows from each man 

 trying to keep the best dogs without any thought of mod- 

 ifying the breed. I may add that, according to Mr. 

 Pierise, there are two varieties of the wolf inhabiting the 

 Catskill Mountains, in the United States, one with a light 



