72 Herediturji Lefthandedness 



On the most probable assumption, namely, that the parents involved 

 are heterozygous, the expected proportion of 1 to 3 is strikingly and 

 suggestively met by 1 to 3"83. Moreover, three fraternities contain 

 lefthanded and righthanded individuals in the exact proportion of 1 to 3 ; 

 and six in the proportion of 1 to 4. 



One hundred and sixty-eight (168) blanks record absence of left- 

 handedness in the direct ancestry; including 51 (2G % + 2.j(/ ) individuals 

 to and including all the great-grandparents, 92 (40$ +52,/) to and 

 including all the grandparents, and 30 blanks (43 lefthanded individuals) 

 with statements, " unable to get information," or " so far as is known." 

 This set includes a fraternity of three lefthanded, including a jjair of 

 twins (Fig. 57). Of another lefthanded individual the statement is 

 given that the lefthanded character is considered a " birth-mark," the 

 mother having been obliged by reason of injuiy to right arm to use 

 the left during pregnancy. Another history, in which no trace of left- 

 handedness is said to appear back to and including the gi'eat- 

 grandparents, includes two lefthanded males among 9 other males 

 and 3 females, including two pairs of ordinary twins (Fig. 58). Still 

 another records an individual " lefthanded from birth," an extraordinary 

 fact. 



This latter group of data admits of three interpretations : (1) absence 

 of hereditary influence ; (2) spontaneous origin of lefthandedness, which 

 may be thereafter transmitted by heredity ; and (3) the " normals " 

 may all be heterozygotes. Moreover, mild degrees of lefthandedness 

 may have escaped notice or may have been ma.sked or lost in later life ; 

 or the information may in a certain number of instances be inaccurate. 

 That it does not indicate absence of hereditary influence appeal's from 

 such pedigi-ees as the one shown in Fig. 59 where the direct ancestors 

 for two generations on both sides are normal. This could be carried 

 backward in time to any previous generation without violence to 

 Mendelian principles. This chart is Fig. 10 of my paper, " Studies in 

 Human Heredity," 1912. These three histories. Figs. 57, 58 and 59, as 

 also Figs. 60 and 61, suggest forcibly that lefthandedness cannot be due 

 to the absence of a factor. As stated in an earlier paper the antithetic 

 condition due to factor absence is probably' ambidexterity. This will 

 be further discussed below. 



The data in charts Figs. 60 to 62 were supplied by Professor 

 F. A. Hodge of Winthrop College, South Carolina. Concerning the 

 penultimate fraternity of six of chart 62 the statement is recorded that 

 these children were " made to wear gloves on the left hand when infants 



