298 UNIVERSITY OF VIRGINIA PUBLICATIONS 



edness is dominant, as is probable, and the mother here is a homozygote, 

 as is indicated, then left-handedness could not appear in the succeeding 

 generation on hereditary assumptions. It would either appear again as a 

 spontaneous variation or by reason of a reversal or low degree of dominance. 

 Of course the mother may be a heterozygote; we have no knowledge of her 

 grandparents; if so, considering the size of the fraternity, the proportion 

 is not greatly at variance with Mendelian expectation. 



©-r-a 



Fig. 7. 



Chart, figure 7, is chiefly interesting as suggesting hereditary ambidex- 

 terity. If we are really dealing with degrees of dominance in left-handed- 

 ness (or imperfection of dominance), as some cases indicate, then ambi- 

 dexterity does not seem to be properlj' interpreted as due to this condition 

 also. Ambidexterity in the limited sense above defined may of itself be 

 hereditary — frequently obscured, however, by reason of neglect of exercise 

 of abilitj' to use both hands. The anatomic basis would be one of cere- 

 bral and brachial sj^nmetrj^; in inverterate left- and right-handedness the 

 anatomic condition would be one of asymmetry. 



This pedigree and that of chart, fig. 34, were so interesting and promis- 

 ing that I made special efforts to secure the most definite and extensive 

 information possible concerning the individuals represented. The result 

 was disappointing. The ambidexterity was in neither case of the theoreti- 

 cal tj'pe indicated above. I hesitate to say now that true human ambi- 

 dexterity as above defined — and as exemplified in infants and the anthro- 

 poid apes* — actually exists in any of my ovm pedigrees, vnth possibly one 

 or two exceptions. They are not theoreticallj^ improbable; but their 

 number is certainly verj^ limited. I am accordinglj^ forced to concur with 

 Hurst that ambidexters as ordinarily foiind are really left-handed individ- 

 uals who have by training acquired skill in the use of the right hand. 



Chart, figure 8, is interesting as sho'n-ing a direct four-generation female 

 line of hereditary left-handedness. I have a similar three-generation male 

 left-handed pedigree. 



* According to J. Cunningham, Journ. of Anthropol. Inst., G. B., vol. 32, 1902. 



