so 



HEREDITY AND SOCIAL FITNESS 



traits being; distinctly lower in this group than they would be were we 

 considering the general population : 



Class 1, indicated by L, includes all those having no ability to handle 

 figures beyond 5; Class 2, indicated by M, includes all those having 

 ability to perform simple multiplication and division, and make small 

 change; Class 3, indicated by H, includes all those having average 

 ability of the general population. The theoretical expectation of the 

 results of matings between members of these classes, based on the 

 relative presence and absence of determiners for calculating ability, 

 has already been given. The progeny of 48 matings of this group, 

 including 177 offspring, may now be distributed among these classes, 

 and the percentage realized compared with the theoretical expecta- 

 tion. Table 1 gives in the first line the expected percentage, and in the 

 second the percentages as realized for the group in question. 



Table 1. — Calculating ability. Rufer group. 48 matings, 177 individuals. 



The realized percentages support the following conclusions: (1) 

 When both parents show^ a low grade of this trait, all the children are 

 similarly of low grade. (2) When both parents show a high grade of 

 this trait, practically all the children are similarly endowed. (3) WTien 

 one parent shows a low grade and the other a medium or high grade, 

 the increase in the percentage of medium and high is proportionate to 

 the grade of the better parent; that is, if the better parent is high 

 grade, there will be fewer low grades among his offspring. (4) Although 

 a small proportion of low grades is produced by the mating of a 

 medium grade \vith a medium or a high grade, here again the propor- 

 tion of low grades is smaller when one consort is high grade than when 

 he is of medium grade (decreasing in the group studied, from 18.50 to 

 13.10). In case he is high grade, there is, too, a considerable increase 

 in the proportion of high grades among his ofi"spring (increasing in the 

 group studied from 11.10 to 47.80). 



The fairly close accord between the theoretical expectation and 

 the realized percentages supports the view that the grade of the ability 

 to calculate depends for its manifestation on the comparative presence 

 or absence of the determiners for this ability. The behavior of these 

 determiners in inheritance is the same as that of the dominants and 

 recessives of the Mendelian hj^othesis. There is segregation here, 

 but not the dominance observed in many of the experimental heredity 



