H. E. Jordan 77 



the basis of faulty record, since later inquiry elicited the information 

 that the " lefthanded " parents were only slightly so, and that they 

 wrote with the right hand. The very fact of the ability to write well 

 with the right hand indicates slight bias, which would be expected 

 to be only imperfectly conformable with strict Mendelian formulae- 

 Chart 67 may perhaps legitimately be similarly interpreted, in the 

 absence of more definite information. The contradictions, Figs. 5, 39, 

 63, 64, 65 and 66, still remain. Here presumably " normal " parents 

 have all lefthanded children. 



Already in my first study I was led to the idea of " degrees of bias." 

 This phenomenon has only become more clear in my second and the 

 present studies. How shall we account for the origin of degrees, and 

 what is their significance in inheritance ? This discussion further 

 involves a consideration of the apparent dominance of lefthandedness in 

 certain strains (Figs. 5, 8, 12, 14, 22, 46). 



Both phylogenetic and ontogenetic facts show that the ancestral 

 condition with respect of use of hand was ambidexterity. Anthropo- 

 hjgical data point in the same direction. Both lefthandedness and 

 righthandedness represent variations from the ambidextral condition. 

 The antithetic condition to both (i.e. the one characterized by nuUiplicity 

 or absence of determiner) is natural ambidexterity. 



The spontaneous origin of lefthandedness and righthandedness in 

 ontogeny suggests, gi'anting full validity to the biogenetic law, that 

 racially these conditions also arose spontaneously, i.e. discontinuously ; 

 not as the result of a slow accumulation of slight variations or fluctua- 

 tions — a mutation, not an acquired character now become hereditary. 

 The fundamental anatomic variation presumably inheres in a foetal 

 asymmetry of the cerebral blood supply producing probably an unequal 

 development (microscopic) of the hemispheres. This phase of the ques- 

 tion is discussed in my former papers. 



The usual variation both phylogenetic and ontogenetic is toward a 

 righthandcd bias. Ancestrally those individuals that varied toward 

 a lefthanded bias came, perhaps, to some extent under the influence of 

 natural selection. Present lefthanded individuals would thus trace their 

 ancestry back to those earliest ancestors who escaped elimination. 



The dominance of righthandedness over lefthandedness is also in 

 accord with the principle of progressive evolution through discontinuity. 

 There can be little doubt that under present conditions of community 

 life, dexterity gives considerable advantage over sinisterity or even 

 perhaps ambidexterity. Indeed righthandedness may easily be conceived 



