NATURAL BREEDING. 125 



the law of Nature is that excellence can only 

 spring from antecedent excellence; consequent- 

 ly we arrive at the rule of practice that no in- 

 ferior animal should ever be used. Shunning 

 in-and-in breeding as a fertile cause of deteri- 

 oration and decay, it must be clearly seen that 

 the necessity which would compel the breeder 

 to use an animal to breed from which was 

 closely akin to the animals crossed with it 

 must be stringent and inevitable. 



Is there, then, no advantage of a positive 

 kind to be derived from outcrosses ? Certainly 

 there is. What has already been said was for 

 the purpose of showing that there was no such 

 claim made for an outcross as has sometimes 

 been made for an incross. But fresh foreign 

 blood, if itself healthy and vigorous, means an 

 access of vigor to a family. Why this is so is 

 perhaps not susceptible of a very clear expla- 

 nation. It is like many another fact in natural 

 history a fact of observation. Like prepotency 

 and atavism, it is well established as a phenom- 

 enon the explanation of which we are as yet 

 unacquainted with. The effect of a cross of 

 very distant blood is sometimes very notable. 

 Animals brought from distant lands and bred 

 together often exhibit remarkable increase of 

 vigor. Increased vigor has great practical value 

 for the cattle-breeder, as some of its most no- 

 table manifestations are increased fecundity, 



