232 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
selection: that is, by individual males having had, in successive gen- 
erations, 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 peculi- 
arities arising and becoming attached to the male sex, which appar- 
ently 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 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 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 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 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 modifying the 
breed. I may add, that, according to Mr. Pierce, there are two 
varieties of the wolf inhabiting the Catskill Mountains, in the United 
States, one with a light greyhound-like form, which pursues deer, and 
the other more bulky, with shorter legs, which more frequently attacks 
the shepherd’s flocks. 
It should be observed that, in the above illustration, I speak of the 
slimmest individual wolves, and not of any single strongly marked 
variation having been preserved. In former editions of this work I 
sometimes spoke as if this latter alternative had frequently occurred. 
I saw the great importance of individual differences, and this led me 
fully to discuss the results of unconscious selection by man, which 
