82 ON THE ORIGIN OF SPECIES 



see peculiarities arising and becoming attached to the 

 male sex in our domestic animals (as the wattle in male 

 carriers, horn-like protuberances in the cocks of certain 

 fowls, etc.), which we cannot believe to be either useful 

 to the males in battle, or attractive to the females. 

 We see analogous cases under nature, for instance, the 

 tuft of hair on the breast of the turkey-cock, which can 

 hardly be either useful or ornamental to this bird ; — 

 indeed, had the tuft appeared under domestication, it 

 would have been called a monstrosity. 



Illustrations of the action of Natural Selection. — 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 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 is hardest pressed 

 for food. I can under such circumstances see no 

 reason to doubt that the swiftest and slimmest wolves 

 would 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 at 

 some other period of the year, when they might be 

 compelled to prey on other animals. I can see no 

 more reason to doubt this, than that man can im- 

 prove the fleetness of his greyhounds by careful and 

 methodical selection, or by that unconscious selection 

 which results from each man trying to keep the best 

 dogs without any thought of modifying the breed. 



Even without any change in the proportional numbers 

 of the animals on which our wolf preyed, a cub might 

 be born with an innate tendency to pursue certain 

 kinds of prey. Nor can this be thought very im- 

 probable ; for we often observe great differences in the 

 natural tendencies of our domestic animals ; one cat, j 

 for instance, taking to catch rats, another mice ; one ; 



