182 SECTIONAL ADDRESSES. 



could not grasp. That the utilisation of these opportunities led to the 

 survival of the bigger-brained beings is also probably true, but it may 

 well have been a physiological change which started the remarkable 

 process. 



The fact that only slight differences in the duration of pre-natal life 

 occur throughout mankind, and that there is a widespread tendency to 

 premature birth about the 220 ±th day suggests that the extension of the 

 pre-natal period is a very old-established feature of mankind, and is a 

 change from a 220 ± days' period. It does not seem useful to speculate on 

 the position of extinct early types of man in this respect, apart from a 

 reminder of the fact that they show some measure of increased growtli of 

 fore-brain as compared with ape-relatives. 



The extension of pre-natal life seems to have induced further important 

 changes which must be mentioned. 



First, it seems that the growth of hair is affected. Downy hair spreads, 

 over the embryo body, becoming very apparent after about the 100th day, 

 and reaching a maximum about the 200 ± th day, but afterwards it becomes 

 less and less, though a little remains throughout life, especially in women, 

 and to some extent in men of the Ainu, Australian, and some European 

 groups. It is much less abundant in the negro, though the Bushman 

 retains some of it, and cases of specially marked persistence of the downy 

 hair occur, with other supposed traces of infantilism, among the Central 

 African pigmies. The indications of hair in lines down the chest and 

 abdomen of a woman depicted at Laugerie Basse (la femme aii renne) in 

 Aurignacian times should be remembered. 



The persistence of an embryonic character such as the downy hair is- 

 a remarkable feature in mankind and an example of partial emancipation 

 from the otherwise general rule that development nearly completes itself 

 by the time of sex-maturity. It will be best at this stage of our ignorance 

 to say merely that there is a pronounced prolongation of features of youth 

 in mankind. 



From about the 170±th day of life-before-birth the growth forms of 

 hair change, and this change becomes very marked after the 200th day. 

 Now in an ape this is near the period of birth and just after it, and the 

 conditions are necessarily those which promote grov/th of protective hair. 

 In man, on the other hand, the conditions rather favour maintenance of 

 the downv hair, though it is not so abundant in the new-born as in the- 

 200 ±th d'ay baby.' 



Thus the lengthening of pre-natal life seems to have been an important 

 factor in the reduction of hairiness in the human race, and also in the 

 retention of a measure of embryonic downiness, and this has increased the- 

 ' tactile ' sensitiveness of the skin of those who retain the downy covering, 

 i.e. especially of children and women. That this has had consequences 

 for the development of the relations between mother and child is almost 

 beyond doubt. 



It is thought by physiologists that the growth of hair absorbs rather 

 a large quantity of energy, and that the thyroid secretion is closely 

 associated with this growth. We shall, therefore, not go far wrong i£ 



^ Friedenthal, H. Das WoUhaarkleid, Das Dauerhaarkleid, &c., 4 Lieferungen^ 

 1908. 



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