XVI ARE ACQUIRED CHARACTERS INHERITED ? 337 



as well as by affording space for the full development of 

 large and well-formed teeth. In the early stages of human 

 progress, when much indigestible food had to be eaten, 

 large bones to be gnawed, and meals to be hastily devoured, 

 the large and powerful jaw would be preserved by natural 

 selection. But civilised man has no need for such a bulky 

 apparatus, hence the average size of the jaw would fall 

 " from the birth-mean to the survival-mean," to use Mr. 

 Lloyd Morgan's neat expression — small-jawed men being 

 at no disadvantage in the struggle for existence ; whence 

 the occurrence among us of very small and very large 

 jaws, though with a lower average than among the 

 Australians. 



The other point — and I believe a very important one — is 

 the diminution, in the mdividual, due to comparative use 

 and disuse. From the time the first teeth are obtained, the 

 jaws are used in mastication many times a day, and the 

 difference in the amount of exertion and strain on the 

 muscles and bone, in the case of a civilised European living 

 mostly on soft or well-cooked food and the savage chewing 

 up tough roots and tearing half-raw flesh from the bones of 

 almost any animal he can kill, must be very great. This 

 difference acting while the bones of the face are growing, 

 in the period between childhood and manhood, and to a less 

 degree, perhaps, on to middle age, would certainly lead to 

 a difference of size — and probably to a large portion of the 

 difference that actually exists — between the jaws of savage 

 and civilised man. If we consider, further, that con- 

 currently with the diminished use of the jaws there was 

 an increased use and development of the brain, it may 

 well be that the j^rocess of reduction of the former was 

 facilitated by the diversion of a portion of the supply of 

 arterial blood to the latter. 



These two causes — cessation of selection or panmixia, 

 and the effect on the individual of greater or less exercise 

 of the parts — are admittedly real causes, their effects can 

 be roughly estimated, and they seem fully adequate to 

 account for the comparatively small difference that 

 actually exists between the jaws of the lowest and highest 

 races now on the globe. 



VOL. I. Z 



