An Introduction to a Biology 



centage of tlie Jersey. And it will take many years to 

 find out. 



It may have occurred to the reader to object that the 

 immediate result of a cross is not by any means always dis- 

 appointing. Of this fact I am well aware. But the value 

 of such crosses is usually due to the fact that first crosses 

 commonly possess great strength, health, and vigour, and 

 is not due to the combination of deliberately chosen desir- 

 able characteristics, which is the subject under discussion. 

 The best bacon, I believe, is produced by first-cross swine : 

 and the same general truth obtains in the case of other stock 

 as well. But the exceptional value of these first crosses must 

 be distinguished carefully from the value belonging to new 

 combinations of characters. The exceptional value of first 

 crosses is due to the fact that they are first crosses ; they 

 have this exceptional vigour and robustness, in virtue solely 

 of the fact that they are first crosses ; and they would not 

 hand it on to their offspring if they were mated together. 

 The value of such first crosses is a flash in the pan. But the 

 value of a new combination of characters brought about in 

 the second hybrid generation has no more to do with the 

 animals being hybrid than the fact that it was necessary to 

 make a cross to bring the characters together. But once 

 these characters have been re-combined in a few individuals 

 and made the foundation of a breed, this particular combina- 

 tion has a value so long as the need which called it into exist- 

 ence persists. 



In conclusion, let me repeat the central idea in this 

 article : that neither the characters of the individual itself 

 nor of its ancestors gives any indication of the value of that 

 individual as a stock-getter. A few records of the milk- 

 production of the daughters of an x'Vyrshire bull are of much 

 greater use as an indication of his value than all the avail- 

 able information with regard to his dam and granddams. 

 You cannot tell what the breeding properties of a beast 

 are until you have tested them. You cannot say whether 



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