i893. NATURAL SELECTION AND LAMARCKISM. 341 



measured by its brain-capacity has greatly increased in size.^ Mr. 

 Spencer cannot possibly say that the thinness and lightness of the 

 bones of the skull are due to disuse, or that the Italian skull has been 

 shortened by disuse. Seeing that Neo-Darwinian factors can reduce 

 skull-bones and soften the frowning glabella so conspicuous in 

 Australian skulls, and that they can also absolutely or relatively 

 shorten the whole skull, why cannot they reduce the jaw-bone and 

 alter its shape and dimensions ? Are we to suppose that a skull-bone 

 that happens to be moveable is thereby exempted from the action of 

 all evolutional factors except use-inheritance ? 



As panmixia and economy must be held to have reduced the 

 weight of the mandible as of other skull-bones, so sexual selection 

 must have modified its shape and size by repressing the brute-like 

 muzzle and large prominent teeth seen in the lower and less 

 humanised races. It has thus favoured the relative prominence of the 

 chin, which is quite as marked a feature in the higher races as the re- 

 duction of the teeth and of the more purely dental portion of the jaw." 

 The eflfect of sexual selection — and of panmixia arising from the 

 survival of delicately-constructed females under male protection and 

 civilisation — is, I think, conclusively shown by the fact that the 

 reduction in female European jaws, as compared with Australian 

 female jaws, is about twice as great as in the case of men. 



The reducing and disturbing influence of disuse during lifetime is 

 also a further cause of decrease which cannot possibly be denied by 

 the Lamarckian. When these various reducing factors are taken into 

 account, what need is there, or indeed what room is there, for the 

 introduction of the Lamarckian factor ? The total reduction in the 

 weight of the male European jaw as compared with that of Australian 

 males, does not seem to be more than 17 per cent., and of this more 

 than a third can be accounted for as being due to a much greater loss 

 of teeth together with consequent alveolar absorption. Another third 

 may fairly be attributed to the Neo-Darwinian factors which had 



8 Excluding the lower jaw, I found that the skulls of European females at the 

 College of Surgeons (mostly Italian) were 12 per cent, lighter than those of 

 Australian females, although the capacity of the cranium had increased by 9 per 

 cent. The weight of male skulls was only reduced by nearly half as much. 



' The reduction of the teeth appears to be greater than that of the jaw. Dr. 

 Macalister found that the area of the crowns of teeth in Englishmen was over 16 

 per cent, less than in Australian males (Nature, Aug. 18, 1892, p. 380). This, in 

 unworn teeth, would correspond with a reduction of about 23 per cent, in cubic 

 measurement or weight — a much greater decrease than had occurred in the jaws 

 that I weighed. A greater reduction of the teeth is e.vactly the opposite of 

 what should have occurred if the Lamarckian explanation were the correct one — for 

 as the teeth emerge from the gum already formed, and are but little, if at all, sus- 

 ceptible of alteration by subsequent use or disuse, they would either not be modified 

 at all by use-inheritance, or at least would be modified much more slowly than 

 the jaw — a circumstance recognised by Darwin, and often insisted on by Neo- 

 Lamarckians, who say that the relatively rapid reduction of the jaw causes a 

 frequent overcrowding of the teeth. 



