Messrs Stratton and Compton, On Accident in Heredity, etc. 507 



On Accident in Heredity, with special reference to Right- and 

 Left-Handedness. By F. J. M. Stratton, M.A., Gonville and 

 Caius College, and R. H. Compton, B.A., Gonville and Caius 

 College. 



[Received 6 June 1910.] 



The characters which an organism exhibits are the product of 

 the action of the environment upon the potentialities inherited 

 from its ancestry. The external conditions may have the effect of 

 preventing the manifestation of an inherited character. For 

 instance, a plant grown entirely in the dark is unable to develop 

 chlorophyll in its plastids. The chlorotic condition induced in 

 this way, though much the same in outward appearance, is of a 

 different nature to that which occurs in a quarter of the seedlings 

 produced by the self- fertilisation of the variegated "aurea" 

 variety of Antirrhinum, where the "presence of chlorophyll" is a 

 Mendelian factor segregating against "absence of chlorophyll*." 



It is thus readily possible for two organisms to exhibit the 

 same peculiarity, in the one case as a result of characters inherited 

 from the parents, in the other case owing to the direct action of 

 external conditions. 



The case of right- and left-handedness seems to afford a 

 striking example of the possibility of the inversion of inherited 

 characters owing to unknown causes, which we may provisionally 

 call " accidents." The difficulty in analysing the facts in human 

 right- and left-handedness is extreme : especially is this the case 

 in discussing the main functional asymmetry in man, since it is 

 almost impossible to allow for the varying influences of education. 

 But this is not the only source of difficulty. Right- and left- 

 handedness are characters which, though sharply distinct, are yet 

 often of an extremely unsubstantial nature as regards heredity. 

 For example, the mode of clasping the hands with fingers inter- 

 locking, varies in different persons: and though the distinction 

 between a person who crosses the right thumb over the left and 

 one who clasps hands in the reverse way is perfectly sharp, yet 

 the real difference between the two persons is obviously trifling. 

 Such an asymmetry we may well expect to be highly susceptible 

 to accidental influences ; and it appears probable that a change of 

 character may readily occur. So that a person naturally right- 

 handed in respect of clasping the hands may through accident 

 become apparently left-handed, and vice versa. 



Two examples may be mentioned in order to emphasize this 

 probability of inversion of character in cases of right- and left- 

 handedness. 



The leaves of many Gramineae (e.g. barley, maize) are folded 



* Baur, Ber. d. d. Bot. Gesellsch. xxv. 1907, p. 442. 



