68 THE THEORY OF NATURAL SELECTION 



that in a savage, since the sense of touch is the only 

 one with which his back is provided, it might be 

 useful for that surface to have acquired a more deli- 

 cate sense of touch than the anterior surface, which 

 is guarded by the power of vision, as well as being 

 more readily explored by the sensitive finger-tips. 

 If such an argument is regarded as far-fetched, so in 

 an equal degree must be any attempt to explain the 

 actually observed distribution through the action of 

 natural selection. 



On the other hand, Spencer points out that the 

 series of parts enumerated in the above table stands 

 in almost exactly the order of the frequency with 

 which the members composing it are actually exposed 

 to tactual experience. 



The tongue is perpetually in contact with the minute 

 unevennesses afforded by the surfaces of the teeth. 



The palm of the hand and the lower joints of the 

 fingers are used chiefly in grasping, and not in the 

 more minute manipulations for which the finger-tips 

 are employed. And the experience of the back of the 

 hand in coming into contact with various irregular 

 bodies is not to be compared with that of the palmar 

 surface, yet it is very much greater than that of so 

 unexposed a part as the middle of the forearm. 



For the carrying on of his argument, Herbert Spencer 

 has shown that increased use of the power of dis- 

 criminating small objects by touch is accompanied by 

 an increased degree of sensitiveness in individuals. 

 Blind people use their finger-tips in this way to a much 

 greater extent than those whose sight is unimpaired. 



