118 FAMILY STUDIES IN BUILD. 



grew slenderer to 5 years, and since then stouter. This seems like a pure 

 line for fleshiness. 



(2) IV 12 $ , is of about the build 2.6 (37) or slightly fleshy. 



(3) IV 15 5 , at 47 years is 153 cm. (60 inches) tall, and weighs 75 kg. 

 (165 pounds) ; build 3.2 (46) ; very fleshy. Like her mother, she was slender 

 until 39 years of age. 



(4) IV 17 $ , at 44 years is slightly fleshy. 



(5) IV 19 9 , is tall and "very slender"; by a very slender husband she 

 has 3 children, all slender. 



(6) IV 20 $ , at 38 years is slender. 



Comment. — Thus, of the 6 children, 1 is very slender, 1 is slender, 2 

 fleshy, and 2 very fleshy — an exceedingly variable progeny. Evidently 

 some of the gametes from both parents are responsible for the result 

 (73 : 690). 



REMARKS. 



The mating of two heterozygous parents produces, in general, an 

 exceptionally variable progeny. This is one of the strongest evidences 

 of the presence of genetical factors in build. The result can not, so 

 far as I can see, be adequately explained on any other than the 

 genetical basis. As an illustration of such variability in full sibs, plate 

 9, figure 4, is striking. Such differences are frequently found in the 

 offspring of heterozygous parents. 



Mating 2. Other Medium x Medium Matings (Table X). 



This mating is important for deciding between the hypotheses (a) 

 that medium build is the heterozygous condition between slender and 

 fleshy; (6) that "medium" represents an hereditary type (biotype) 

 as truly as slender does; (c) that the "medium" group is a combina- 

 tion of cases of the heterozygous condition and a distinct biotype. 



First, it appears that the mating is the commonest one in our 

 records, except medium X fleshy. But this is to be expected, inas- 

 much as the medium grade of build is the commonest grade. 



Second, the variability of the progeny is small, 4.05 ±0.11. The 

 only mating that has a less variable progeny is S X S, 2.41 ± 0.17. 

 This result, shown in table 12, indicates that the persons of medium 

 build are, for the most part, not heterozygous, but belong to a distinct 

 biotype. On the other hand, M X M matings from table X, selected 

 mostly on account of dissimilar build of parents, give progeny dis- 

 tributed nearly in a 1 : 2 : 1 ratio, such as is got in the second gen- 

 eration of a mono-hybrid. It seems probable, accordingly, that 

 hypothesis (c) is correct, but that the cases of medium that belong to 

 a distinct biotype are much more numerous than the cases of medium 

 parents who are heterozygous. 



