296 DARWINISM STATED BY DARWIN HIMSELF. 



P ' 342 When we direct our whole attention to 

 any one sense, its acuteness is increased ; and 

 the continued habit of close attention, as with blind 

 people to that of hearing, and with the blind and deaf to 

 that of touch, appears to improve the sense in question 

 permanently. There is, also, some reason to believe, 

 judging from the capacities of different races of man, that 

 the effects are inherited. Turning to ordinary sensations, 

 it is well known that pain is increased by attending to it ; 

 and Sir B. Brodie goes so far as to believe that pain may 

 be felt in any part of the body to which attention is 

 closely drawn. 



A NEW ARGUMENT FOR A SINGLE PARENT-STOCK. 



Expression I have endeavored to show in considerable 



tions 6 m °' detail that all the chief expressions exhibited 

 page 361. by man are the same throughout the world. 

 This fact is interesting, as it affords a new argument in 

 favor of the several races being descended from a single 

 parent-stock, which must have been almost completely 

 human in structure, and to a large extent in mind, before 

 the period at which the races diverged from each other. 

 No doubt similar structures adapted for the same purpose 

 have often been independently acquired through variation 

 and natural selection by distinct species ; but this view 

 will not explain close similarity between distinct species 

 in a multitude of unimportant details. ISTow, if we bear 

 in mind the numerous points of structure having no rela- 

 tion to expression, in which all the races of man closely 

 agree, and then add to them the numerous points, some 

 of the highest importance and many of the most trifling 

 value, on which the movements of expression directly or 

 indirectly depend, it seems to me improbable in the high- 



