EFFECT OF SELECTION 107 



correctly represented by Pearson's fraction, even 

 though their individual contributions are not always 

 the same. 



Let us, then, briefly examine some of the further 

 conclusions which have been drawn from the data of 

 the biometricians. 



Assuming the law of ancestral heredity, Pearson has 

 arrived at very interesting conclusions with regard to 

 the effects of artificial selection when the correlation 

 coefficients have those values which have been actually 

 found for them in the case of the human race. In the 

 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 : 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 inches 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, 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 



