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 sufliciently 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 (i), 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 «o«-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 



* 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 a standard of comparison 

 for more delicate investigations. 



•' Are the Effects of Use ami Disuse Inherited ? (" Nature " Series.) 



