No. 564] INHERITANCE OF LEFT— MA NDEDNESS 733 



to be accounted for as just stated. Probably the most 

 valuable parts of the statistics are the figures showing 

 families with left-handed children and also the total 

 number of left-handed children in the population. 



Natural and Acquired Left-handedness. — Most right- 

 handed people can be taught to use the left hand for many 

 purposes, and conversely left-handed people may learn 

 to write and perform various acts of skill with the right 

 hand. But aside from these rather unusual cases there 

 are many individuals who are naturally right-handed and 

 do most of their work with the right hand. Others are 

 left-handed by nature. Left-handedness seems to be con- 

 nected with a more highly developed condition of the 

 right cerebral hemisphere. Evidence in support of this 

 view is found in a number of cases of aphasia connected 

 with left hemiplegia. The left motor area of the cortex, 

 as is well known, is associated with speech in most indi- 

 viduals. Hence a lesion of this area results in aphasia 

 and paralysis of the right side of the body. When similar 



5. 12Rr X 12Br = 144 



6. 12Kr X 4rr = 4S 



7. 4rr X 9FR= 36 



8. 4rr X 12Er = 48 



4Kr X 4Er = 12 right-handed, 4 left-handed 

 47?r X rr = 2 right-handed, 2 left-handed 

 rr X4ffr= 2 right-handed, 2 left-handed 

 rr X rr = right-handed, 1 left-handed 

 16 9 



The children in these families would then be expected in the ratios of 

 16 : 9, or 64 per cent, right-handed, 36 per cent, left-handed. 



7 Only in the following matings could left-handed children appear: 

 12Kr X 12ffr=10S right-handed, 36 left-handed 



