78 HercdUanj Lr/f handedness 



of as having contribntcd t-<i a cinisidcrable degree to the attainment of 

 the present level of civilization. The telcological significance of the 

 dominance of righthandcdness is obvious. However, the cause of 

 prepotency is here as ob.scui'e as elsewhere. The evidence on this point 

 is conflicting; now ancestral conditions (racially older) seem to be 

 dominant, m other instances the new, and again the more intense, are 

 prepotent. Progress by discontinuous variation would seem to be 

 possible only through the prepotency of determiners signifying improved 

 adjustment. 



Genetic studies of bias toward use of one or the other hand promise 

 to throw .some light on the (piestion of the stability of "determiners" or 

 " genes." Degrees of prepotency of characters, so strikingly evident in 

 the case of the heredity of use of hand, suggests considerable lability of 

 genes. 



Elucidation of the whole matter proceeds with inneh plausibility 

 from the recent suggestion by Miss Elderton, that dominance may not 

 attach to a character but to the individual with the character, "i.e. that 

 the same character can in certain individuals be dominant and in others 

 be recessive," p. 34. Whether by reason of a numerically })re])onderant 

 variation towards dexterity relative to sinisterity, or a numerically equal 

 but more decided bias in that direction, righthandcdness early came to 

 be the numerically predominant condition, now present approximately 

 in the ratio of 4 to 1. Under later civilization lefthandedness became 

 an increasingly greater handicap. Thus individuals in whom this 

 handicapping character of great intensity was dominaul may have been 

 eliminated through differential selection. In this wise only recessive 

 lefthandedness of high degree has come to remain almost exclusively, 

 and the ideas of dominance and recession have come to be attached to 

 the character itself. Less extreme degree of lefthandedness due to a 

 greater power of adaptability and training may thus have to some extent 

 remained of a dominant nature. 



Thus the parents in charts 63 to 66 may possibly have been left- 

 handed individuals of so slight degree as to have escaped notice as such 

 in childhood or forgotten at maturity, but of dominant nature ; then, 

 whether duplex or simplex, all the children would be expected to be 

 lefthanded. Likewise in pedigrees like Figs. 67 and 77 the parents 

 may be simplex dominants (for lefthandedness), thus of mild degree, 

 and their naturally lefthanded offspring of slight bias may by slight 

 or even unpremeditated training have been made to acquire right- 

 handedness. 



