STUDIES IN HUMAN HEREDITY 



301 



Chart, figure 10, is of considerable importance. It illustrates very 

 well how the use of restricted pedigrees may lead to false inferences. If 

 we considered only the direct ancestrj^, both paternal and maternal, of 

 A (who is inveteratelj^ left-handed and even writes with the left hand), — 

 and this is all that is f requentlj^ Imowii or given in brief family histories — 

 the left-handed condition here would appear to have arisen spontaneously, 

 and to be without hereditary aspect. The mother has no left-handed 

 brothers or sisters. Nor was the father, or any of the grand-parents on 

 either side, left-handed. The more extensive pedigree chart shows, how- 

 ever, that on both sides there were left-handed relatives. My informant 

 states that there are still other left-handed collateral relatives not here 

 shown. The chart indicates that both parents were probably heterozy- 

 gous; and left-handedness in some of the children is thus to be expected. 



•-I-D 



•-T-a 



i(2 



ffi^ 



-^■2 Other children of un- 

 known number, condition 

 and sex. 



Fig. 11. 



Fig. 12. 





Fig. 13. 



■a 



«45^ 



Fig. 14. 



Charts, figures 11, 12, 13 and 14, are additional instances of the appar- 

 ent dominance of left-handedness. In 12 the mother "corrected the left- 

 handedness, making them all ambidextrous." The ambidexterity here 

 alluded to is however more probably simply ability to perform some efforts 

 with the right-hand, others with the left-hand. The final fraternity of 

 chart 14 again indicates an RR X DR cross, which is hkely in view of the 

 pedigree of the mother. 



Charts, figures 15, 16 and 17, represent an interesting type of left- 

 handed pedigree. In every case neither parent had left-handed brothers 

 or sisters (indicated by character Z). In 15 and 16 the parents are hetero- 

 zygous dominants; and at least one left-handed offspring was to be expected 

 in a fraternity of four. 



