No. 564] INHERITANCE OF LEFT -HA NDEDNESS 735 



lesions of the right cerebral cortex result in paralysis of 

 the left side and also in aphasia, it is sometimes found 

 that the persons thus affected were naturally left-handed. 

 I am informed by my colleague, Dr. 0. M. Gilbert of the 

 department of medicine of this university, that this con- 

 nection of left-handedness with a speech center on the 

 right side of the cortex is well attested. 



A certain number of persons consider themselves to be 

 "ambidextrous" and claim that they are not naturally 

 either right-handed or left-handed. It is, however, diffi- 

 cult for one to know his own original condition with 

 regard to the use of the hands, since in most homes the 

 child is taught early the use of the right hand in taking 

 up a spoon or cup. I suspect that the "ambidextrous" 

 persons are really left-handed by nature. 



Mendelian Explanation of Heredity of Left-handed- 

 ness. — A study of the accompanying tables will suggest 

 that left-handedness is a Mendelian recessive. It belongs 

 to that group of characters which may show themselves 

 in families where neither parent is affected, and some- 

 times in families with no affected ancestors for a number 

 of generations. In the 305 families there are only two 

 reported as having both parents left-handed. If the con- 

 dition is a Mendelian recessive the children in these 

 families should all be left-handed. According to the 

 report, however, one child is right-handed. Of course it 

 is possible that one of the parents was by nature right- 

 handed. Possibly some heterozygous (simplex) persons 

 may easily learn to use the left hand. 



Presentation of Material.— The material collected has 

 been classified in such manner that it can be made use of 

 by others who may be studying the subject. In some of 

 the tables I have indicated the expected percentages if 

 the population were to consist of the three Mendelian 

 types of individuals in the following proportions, viz. : 



(a) 4RR : 4Rr: rr, 



(b) 9RR:12En4rr. 



