10 THE FACTORS OF ORGANIC EVOLUTION. 



and by citing not infrequent cases of individuals remark 

 able for their mental powers, and at the same time 

 distinguished by jaws not less than the average but 

 greater. Again, if sexual selection be named as a possible 

 cause, there is the reply that, even supposing such slight 

 diminution of jaw as took place in a single generation to 

 have been an attraction, yet the other incentives to choice 

 on the part of men have been too many and great to allow 

 this one to weigh in an adequate degree ; while, during 

 the greater portion of the period, choice on the part of 

 women has scarcely operated : in earlier times they were 

 stolen or bought, and in later times mostly coerced by 

 parents. Thus, reconsideration of the facts does not show 

 me the invalidity of the conclusion drawn, that this 

 decrease in size of jaw can have had no other cause than 

 continued inheritance of those diminutions consequent 

 / on diminutions of function, implied by the use of 

 selected and well-prepared food. Here, ~^oW5Tef7&quot; my 

 chief purpose is to add an instance showing, even 

 more clearly, the connexion between change of func 

 tion and change of structure. This instance, allied in 

 nature to the other, is presented by those varieties, or 

 rather sub-varieties, of dogs, which, having been household 

 pets, and habitually fed on soft food, have not been called 

 on to use their jaws in tearing and crunching, and have 

 been but rarely allowed to use them in catching prey and in 

 fighting. No inference can be drawn from the sizes of the 

 jaws themselves, which, in these dogs, have probably been 

 shortened mainly by selection. To get direct proof pf the 

 decrease of the muscles concerned in closing the jaws or 

 biting, would require a series of observations very difficult 

 to make. But it is not difficult to get indirect proof of this 

 decrease by looking at the bony structures witli which 

 these muscles are connected. Examination of the skulls 

 of sundry indoor dogs contained in the Museum of the 

 College of Surgeons, proves the relative smallness of such 



