OF A CERTAIN PENNSYLVANIA FAMILY. 



81 



Studies; the single determiner or the halving of the total number of 

 determiners producing a lower grade of the trait than when a greater 

 number are present. The case would appear to be analogous to that 

 observed in the inheritance of eye color, where the single dose of the 

 determiner for pigmentation produces light-brown eyes, while the 

 double dose produces darker brown. 



A similar study of the distribution of grades of calculating abihty 

 was made of the Riel group. 32 famihes, including 120 individuals, 

 were distributed among three classes, only in this instance different 

 values were assigned to the three classes L, M, H. L includes all those 

 with ability to perform simple multiplication and division and make 

 small change and hence equals class U for Rufer group; M includes 

 ail those possessing average calculating abihty, hence equals class H 

 Rufer group. H equals those with ability above the average. The 

 distribution of progeny from the various types of mating is shown in 

 table 2. 



Table 2.— Calculating ability. Rid Group. 82 matings, 120 individuals. 



The realized percentages from this group support all the conclusions 

 drawn from the study of the Rufer group, with the exception of the 

 second conclusion, the mating of high ability with high abihty not 

 having occurred here. 



The assumption of a unit-character of varying potency ,^ or better, 

 of a number of determiners which behave in unit-like fashion, would 

 appear to explain the phenomenon of inheritance for calculating 

 ability as observed in these networks. So long as low ability mates 

 with low ability there can be no advance in this faculty, since the germ- 

 plasm remains relatively empty, so far as determiners for this faculty 

 are concerned. Such a condition is illustrated in Line E. However, 

 let successive matings occur between those having low ability and those 

 of fair or good calculating ability belonging to strains showing this 

 abihty, then the unit of higher potency will replace that of low potency 

 in an increasing proportion of the offspring: this will be equivalent 

 to the gradual elimination of the unit of low potency, and will bring 

 about improvement in the grade of calculating ability. 



If we adopt the hypothesis of the unit-like series, we may conceive 

 the number which stands for presence in a slight degree, to be replaced 

 by the greater number which stands for good ability in the better 



