200 CAUSES OF VARIATION 



opportunity for selection in the latter instance, with none what- 

 ever in the former ! The first untimely death would render the 

 line extinct, which is perhaps the best fate that could overtake 

 a race which at best is able only to hold its initial number good. 



Of course artificial conditions have been assumed in order to 

 bring out the principle. It does not work out in this regular 

 and evident manner in our herds, but the principle of genetic 

 selection is at work, nevertheless. It would be fortunate if it 

 were more evident, for the herds are few that do not contain a 

 large proportion of females that contribute nothing to the real 

 line of descent, though they now and then give birth to excep- 

 tional individuals. The quality is good, but the rate of repro- 

 duction is too low. 



How many a breeder has spent fruitless years in ineffectual 

 attempts to build up a strain excellent in itself but essentially 

 infertile ! Witness the fate of that remarkable family of short- 

 horns, the Duchess. This famous family, in its glory, was never 

 surpassed, yet it was genetic selection that exterminated the 

 line. Fortunate indeed is the breeder who knows this principle 

 and realizes its full power whenever he finds himself opposed 

 by it. 



The student must not get the impression that genetic selec- 

 tion is an enemy only. A prolific line tends as strongly to 

 establish and maintain itself as does a barren one to rush head- 

 long to extinction. Genetic selection is therefore a friend pow- 

 erful for good, as well as an enemy powerful for evil ; but it is 

 as quiet and unobtrusive in the one relation as it is insidious 

 in the other. The breeder has only to be eternally conscious of 

 the fact that if he is to succeed he must have numbers, not 

 occasional births, but regular and generous. Then he may be 

 sure that he is not trying to do a thing on which nature has 

 set the seal of her disapproval through non-production. However 

 worthy and however valuable intrinsically the strain may be, it is 

 worthless unless he can produce it with certainty and in any 

 desired numbers. " Beware of the shy breeder, and treasure the 

 old female that breeds regularly and true." This doctrine estab- 

 lishes a cooperation with nature that insures results, and with- 

 out it genetic selection will work against us, not for us. 



