EFFECT OF SELECTION 115 



statement which follows, ancestors are supposed to 

 have been selected showing in each generation a devia- 

 tion h from the general mean of the population. Thus, 

 suppose the character selected to be stature 2 suppose 

 the mean height of the population to be 6 feet, and 

 the selected individuals to be 6 feet 6 inches high ; h is 

 then 6 inches, and only individuals of a height of 

 6 feet 6 niches would be selected as parents in each 

 generation, so that after three generations of selection 

 we should be dealing with children whose parents, 

 grandparents, and great-grandparents were all of this 

 particular height. 



Pearson calculates that after one generation of 

 selection the immediate offspring will show 0-62 of 

 the character selected (0-62 h). After two generations 

 they will show 0-82 h, after three 0-89 h t and after a 

 great number of generations 0-92 h. Thus in a com- 

 paratively small number of generations the development 

 of a character may be raised to within 90 per cent, 

 of the value selected, but, after this, further selection has 

 very little effect. If selection is stopped after one 

 generation, and the selected stock is then inbred, it 

 was calculated that the first generation of inbred stock 

 would show 0-59 h y the second 0*56 h, the third 0-52 h t 

 and the tenth 0-35 h. If, on the other hand, in- 

 breeding Was started after the selection had continued 

 for a large number of generations, the first generation 

 of inbred stock will show 0*86 A, the second 0-81 h, 

 the third 077 h, and the tenth 0-51 h. So that in- 

 breeding of a selected stock is followed by a very 



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