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UNIVERSITY OF VIRGINIA PUBLICATIONS 



character. What motive first caused man to use the right hand almost 

 exclusively for executions of skill and force, is a problem shrouded in mys- 

 tery. Moreover, the stimulus may not have been external at all; it may 

 have been an internal stimulus resting upon an anatomic variation of 

 the vascular system, for example. Right-handedness may have been a 

 mutation from a primitive ambidextral condition, left-handedness repre- 

 senting more nearly the primitive ambidextral condition — or a reversed 

 mutation. Further speculation would be fruitless at present. It need 

 merely be pointed out here that dexterity may be represented by a germi- 

 nal factor which comes to expression only in later stages of development, 

 passing through a more primitive stage of ambidexterity — ^just as all 

 definitive conditions are the result of a process represented by steps through 

 more primitive conditions. The factor may also be readily responsive 

 to influences of later development, which may change its hereditary ten- 

 dency, as seems to have been the case in those instances of identical twins 

 where one is left-handed and the other right-handed. If right-handedness 

 is an acquired character it was acquired relatively late in racial history, and 

 in heredity would be expected to show varying degrees and grades of 

 expression. A careful weighing of all the evidence favors more strongly, 

 however, the idea of the appearance of an internal anatomic variation, 

 causing general right-handedness and occasionally (as a reverse variation) 

 left-handedness. This position must further account for the fact that the 

 assumed variation in the vascular supply of the cerebral hemispheres caus- 

 ing left-handedness antedates by several months the expression of the fmic- 

 tional condition. This, however, is perhaps only what should be expected, 

 since the altered function should appear only after the anatomic change 

 has had time to work a summation of effects. 



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Fig. 10. 



