1893. 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.7 
The effect 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 
6 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 g per 
cent. The weight of male skulls was only reduced by nearly half as much. 
7 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 exactly 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. 
