September 23, 1904.] 



SCIENCE. 



405 



increasing complexity of hair slope. With 

 reference to man the statement is made that 

 man has ' acquired, by some means or other, 

 and transmitted, a very remarkable series of 

 changes both from the primitive and from the 

 Simian type.' 



Those hair tracts which have been acquired 

 by ' morphological changes ' are described as 

 merging somewhat into those acquired throtigh 

 the effect of use or habit (i. e., mechanical 

 forces), ' the frontiers between the two being, 

 of course, somewhat vague.' In fact, there is 

 no criterion whatever given by means of 

 which one may know which deviations from 

 the primitive direction are due to these ' mor- 

 phological changes,' the whole distinction be- 

 ing, so far as I have been able to determine, 

 a purely arbitrary one. 



Kidd's theoretical discussion involves the 

 following line of argument : 



Deviations from the primitive direction of 

 hair can not, even in the case of long-haired 

 forms (with the single possible exception of 

 the extensor surface of the ulna of certain of 

 the Anthropoidea) be considered an adapta- 

 tion. These deviations can, therefore, have 

 no selective value and can not, like the primi- 

 tive direction, be accounted for by any process 

 of selection, natural, sexual or germinal. 



The correlation between the deviations from 

 the primitive direction and the mechanical 

 forces exerted upon certain areas of the body 

 indicates that these deviations are due wholly 

 to such forces. Deviation from the primitive 

 direction is, however, not easily produced and 

 occurs only when there is a decided prepond- 

 erance of force in a single direction. 



The existence of these deviations in fetuses 

 and in the new-born indicates their inherit- 

 ance. Hence in the realm of hair direction 

 the Lamarckian principle of the inheritance 

 of acquired characteristics is established. 



Kidd claims for his views no opposition 

 whatever to Darwinism. On the contrary, his 

 course of reasoning seeks to establish a fusion 

 between the two great principles of natural 

 selection and use-inheritance. The issue is, 

 however, distinctly with Weismannism, which 

 claims the non-inheritance of acquired char- 

 acters as an integral part of its theory. 



It is obvious that Kidd has laid before us 

 a large number of extremely interesting facts 

 showing an indisputable correlation between 

 the direction of hair and the mechanical pres- 

 sure from various causes, exerted upon the 

 skin. His explanation of this correlation can, 

 however, hardly be accepted as final at the 

 present stage of the investigation, and the 

 following criticisms are offered merely as sug- 

 gestive of further research which the field 

 demands : 



1. There is no recognition in Kidd's discus- 

 sion of a possible difference between the direc- 

 tion of the external portion of the hair and 

 that of the follicle. Before any of the varia- 

 tions in hair direction upon the human scalp 

 can, for example, be logically attributed to 

 methods of parting and dressing the hair, it 

 should be shown that a change in the direc- 

 tion of the external, more or less wiry portion 

 of the hair produces a change in the direction 

 of the follicle. In the case of the sloth, also, 

 it is unquestionably a fact that in obedience 

 to gravitation the long hair hangs down, in 

 the habitual inverted position of the body. 

 It would be exceedingly interesting, and, for 

 the validity of Kidd's argument, of absolute 

 importance to know (1) whether the follicles 

 themselves have this same direction and (2) 

 whether this direction occurs in the fetus. 

 No one, indeed, will deny the temporary action 

 upon hair of gravitation or any other external 

 force which may be applied to it; but to show 

 that these forces acting upon the long external 

 hair produce any real change in the direction 

 of the growing portion of the hair, which 

 alone constitutes hair direction as used mor- 

 phologically, is a necessary link in the chain 

 of reasoning which seeks to prove that con- 

 genital hair direction of an animal can be 

 attributed to mechanical forces acting upon 

 the external portion of the hair of its an- 

 cestors. 



The failure to recognize the possible dif- 

 ference between the superficial condition and 

 the real hair direction may be further illus- 

 trated by Kidd's treatment of the mole. He 

 says : " The skin of this animal possesses that 

 unusual quality of hair resembling velvet and 

 has no fixed slope of hair, as is the case in 



