340 NATURAL SCIENCE. May, 
as in the tip of the tongue, where points only one twenty-fourth of an 
inch apart can be felt as separate impressions. But is it likely that 
mere use will diminish the size and multiply the number of the 
separate structures on which distinct sensations depend? Mr. 
Spencer leads us to infer that such multiplication had taken place in 
four cases which he tested+; but the assumption that increased use 
converted twelve tactile areas into fourteen or seventeen has some- 
what of the same intrinsic improbability as the idea that a man by 
using his five fingers sufficiently might convert them into six or eight. 
Though processes of multiplication by splitting or subdivision are 
perhaps conceivable, Foster’s explanation seems much more reason- 
able, and the supposed value of the whole case as an inferential 
proof of use-inheritance becomes correspondingly doubtful. 
The next example or proof of use-inheritance to which we are 
referred is the decrease of the human jaw in civilised races. I have 
already dealt with this case elsewhere,5 and have attributed the 
changes more especially to the combined effects of (1), panmixia ; 
(2), sexual selection; and (3), the natural selection of an economy of 
structure which: would promote lightness and agility besides saving 
some slight amount of nutriment. Panmixia, it seems, is a factor 
which Mr. Spencer had ‘‘ excluded as impossible.” But it is obvious 
that Natural Selection may favour large and efficient organs of masti- 
cation and strong unbreakable jaw-bones among low savages almost 
destitute of tools and cookery, living at times on the rudest and 
harshest food, and often falling victims to violence or accident. If 
Natural Selection has done this—which I presume will not be disputed 
—then it is perfectly adequate to cause some part of the difference 
between the jaws of savages and of long-civilised races; and it is 
only saying the same thing in a slightly changed form when we con- 
tend that panmixia, in the form of xon-selection of large teeth and 
jaws, is one of the causes of the relative smallness of the teeth and 
jaw in civilised races. How far panmixia alone can reduce size is a 
matter not easily susceptible of clearly demonstrative proof, but it is 
at least obvious that the comparative cessation of selection of large 
strong teeth and jaws leaves the field more open than before for the 
action of reducing factors such as economy. [If it still be said that 
Neo-Darwinian factors cannot reduce the jaw, we may point to the 
decisive fact that the other bones of the skull are distinctly lighter in 
Europeans than in Australians and negroes, although the skull as 
4 As no measurements were made before the increased use, the ‘‘clear proof’’ is 
clearly imperfect, for there is nothing to show that the sensitiveness of the finger- 
tips in the two blind youths and the two skilled compositors was not entirely con- 
genital. Compositors capable of becoming “‘skilled,’’ probably started with a 
sensitive tactile organisation. Weber’s twelfth of an inch, too, is obviously only an 
approximate measurement, and ought not fairly to be made astandard of comparison 
for more delicate investigations. 
5 Ave the Effects of Use and Disuse Inherited ? (‘‘ Nature"’ Series.) 
