20 



BULLETIlSr 1121, U. S. DEPARTMENT OF AGEICULTTJEE. 



THE PERCENTAGE RAISED OF ALL YOUNG BORN. 



The percentage raised of all young born is simply the product of 

 the two which we have been considering. Figure 10 brings out the 

 superiority of crossbred young from inbred dams (CO, CA) over 

 inbreds, and the still greater superiority of crossbred young from 

 crossbred dams (AC, CC) . The record of the first generation inbreds 

 from crossbred dams (Cl) is a little higher than theory would indicate. 

 There is, however, a decline in the next generation of renewed inbreed- 

 ing (C2) of almost the expected amount. It is noteworthy that the 

 record of the random-bred stock (B) is practically reached by cross- 

 breeding involving only three or four of the inbred families. 



One of the most striking results is the great advance of the cross- 

 breds over the best of the inbred families. The superiority of the 

 best inbred family over the average is increased more than fourfold. 



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Fig. 10.— The percentage raised to ^3 days of all young born, 1916-1919. Indices correcting for eflects of 

 size of litter and seasonal conditions. (See Fig. 8 for explanation of symbols.) 



This is a much greater relative increase than shown in the case of 

 either component percentage. The reason is easily discovered. An 

 inbred family which is above the average in percentage born alive 

 is perhaps more likely than not to be below the average in the per- 

 centage of these raised. It thus comes about that there is no more 

 differentiation among the families in the total percentage raised than 

 in either component. The second generation crossbreds, on the 

 other hand, are superior in both components and thus very much 

 superior in the product. We have here a good illustration of the 

 way in which a great superiority of a crossbred stock over the best of 

 its ancestral inbred families with respect to a complex character 

 may be built up out of mere dominance of vigor over weakness in a 

 number of more elementary characters which are distributed at 

 random among the inbred families. Further illustration of this 

 point will be taken up later. 



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