76 Hereditarji Leftlumiledness 



number of apparently serious contradictions may peiliaps still give some 

 gi-ound for question. However, the main mass of data points to strict 

 Mendelian hereditary conduct. The proportion of 1 lefthanded to 1^ 

 righthanded obtained in both of my earlier studies when all histories 

 were included cogently suggests the operation of Mendelian laws, when 

 account is taken of the fact that the majoi-ity of the crosses were either 

 DR X Dlt (1 : 3) or DR x RR (1:1). Moreover, a considerable number 

 of histories gave approximately the expected proportions for such 

 crosses, where the most pi'obable condition of the [)aients was indicated 

 by the ancestry. 



Major C. C. Hurst, on the basis of a study of a number of pedigrees, 

 confirms my conclusion that lefthandedness is a Mi'ndelian recessive'. 

 Dr E. Stier's pedigi'ee.s of double lefthanded matings (6 cases) force the 

 same conclusion, when allowance is made for occasional imperfection of 

 dominance or slight degi-ees of bias. In no instance are all of the 

 offspring lefthanded ; but with one exception the majority are left- 

 handed. 



My present study gives additional, and more complete, confirmation 

 of my earlier conclusion. A general survey of these charts permits 

 no doubt that lefthandedness is hereditary. This conclusion is further 

 suggested by cases of duplicate twins, where both members of the pair 

 are lefthanded (Figs. 22 and 57 — exception Fig. 78). When therefore 

 lefthandedness appears in a fraternity, at least one of the parents is 

 simplex for the lefthandedness factor, frequently perhaps both. Sum- 

 marizing the 69 pedigi'ees in the group where the ancestry is said to be 

 normal, and where the fraternities contain four or more individuals, 

 the ratio of lefthanded to righthanded is as 1 : 3\5G (page 73). This 

 is so close to Mendelian expectancy for DR x DR crosses as to furnish 

 almost a demonstration of the actual fact. The slight preponderance of 

 righthandedness is undoubtedly to be accountetl for by the occasional 

 DD X DR crosses with possible imperfections of dduiinance. Moreover, 

 the inclusion of sixteen 1 : 3 ratios, and the same number of 1 : 4 ratios 

 still more firmly supports the conclusion. Likewise, the ratios of the 

 other two tables above discussed and the average of all, 1 : 3'31. 

 A ruimber of the pedigi'ees here charted give also the exact ratio 

 expected on Mendelian assumptions. 



Again, double lefthanded matings give complete lefthanded frater- 

 nities (Figs. 5, 16 — almost, 75, and 76), as expected from pure recessive 

 parents. The apparent contradiction. Fig. 77, is to be explained on 



' Likewise more recently Professor Francis Ramaley (Am. Nat., Dec. 1913). 



