294 UNIVERSITY OF VIRGINIA PUBLICATIONS 



The pedigree charts here given and discussed are for the most part 

 contributed by students of the University of Virginia. I take this occa- 

 sion to express my best thanks to all who have taken an interest and aided 

 in this work. 



LEFT-HANDEDNESS. 



In my earlier paper I* showed that left-handedness is hereditary, prob- 

 ably following Mendelian principles of segregation and dominance. The 

 conclusion was arrived at that, fundamentally, the inheritance of left-hand- 

 edness was the inheritance of a condition of reversed differential cerebral and 

 brachial development (nutrition), consequent upon a variation in the vascu- 

 lar system. t Accordingly, in the last analysis, left-handedness was thought 

 to signify an anatomic variation; and its "determiner" to be the factor 

 underlying a change of structural relationships. In six selected cases the 

 Mendelian expectation was fulfilled, assuming right-handedness to be domi- 

 nant. Mendelian inheritance was strongly suggested also by the propor- 

 tion of one to one and a half of left- to right-handed children in child- 

 ships of four or more individuals. Ambidexterity was tentatively regarded 

 as due to an imperfection of dominance producing functional symmetry. 



Major C. C. HurstJ has recently reported a number of pedigrees which 

 he interprets in a similar manner. He disagrees, however, with respect 

 to ambidexterity. Hurst regards ambidexterity as left-handedness plus 

 acquired right-handedness. If this is correct, ambidexters are rightly 

 classified as left-handed individuals. This is undoubtedly true of the 

 majority of cases. But an intelligent discussion of this point demands 

 a definition of ambidexterity. 



Popularly, a condition where one hand is used for some things and the 

 other for other things is called "ambidextrous." True ambidexterity, 

 however, consists in the ability to do all things equally well and deftly with 

 either hand. Ability to execute halves of bilaterally synametrical efforts 

 at the same time (e.g., as in drawing) is likewise an aspect of ambidexterity. 

 Even this ability may be to some extent acquired. However, the born 

 ambidexter acquires this skill naturally and more readily. Such are not 

 truly sinistro-manual. True, they may not really be of the nature of im- 

 perfect dominants. But a family history in which ambidexterity, as such, 



* American Breeders' Magazine, 2: 1 and 2, 1911. 



t Lueddeckens (Fritz) likewise traces the cause of right-handedness to a con- 

 dition of asymmetrical embryonic cerebral vascular supply. Bechts- und Knks- 

 hdndigkeii, Leipzig, 1900. 



X The Eugenics Review, 4: 1, 1912. 



