i8o THE FIRST PRINCIPLES OF HEREDITY 



the dregs of society (whosoever they may be), is to prevent 

 them from multiplying by propagating their own kind. 

 On the other hand, it is apparent that, if we desire to 

 breed a high type of individuals, the chances of success 

 are very much greater if we select for propagation fathers 

 of a high type, and even greater still, as Galton has 

 shown, when there is coupled with it talent from the 

 mother's side. 



Additional weight is added to these deliberations by other 

 facts already adduced with regard to the action of selection 

 on the rearing of stock, as elaborated by Pearson. It has 

 been shown in Chapter IX. that, while good stock springing 

 from mediocre ancestry regresses within a few generations 

 to the mediocre level of its ancestry, good stock bred from 

 a succession of selected generations finally regresses barely 

 I per cent, from the selected value. In other words, by 

 selecting good stock for a few generations we can insure 

 that they will breed practically true for an infinite number 

 of generations. " Looked at from the social standpoint," 

 says Pearson, " we see how exceptional families, by careful 

 marriages, can even within a few generations obtain an 

 exceptional stock, and how directly this suggests assorta- 

 tive mating as a moral duty for the highly endowed. On 

 the other hand, the exceptionally degenerate, isolated in 

 the slums of our modern cities " (and we would add, not 

 only in the slums), " can easily produce permanent stock 

 also — a stock which no change of environment will per- 

 manently elevate, and which nothing but mixture with 

 better blood will improve. But this is an improvement 

 of the bad by a social waste of the better. We do not want 

 to eliminate the bad stock by watering it with good, but 

 by placing it under conditions where it is relatively or 

 absolutely infertile." 



Further, Mendelism, not less than aU the other evidence 

 already brought into array, proves conclusively how the 

 nature of the progeny depends essentially on the gametic 

 constitution of the parents. Nay, it has been shown that 



