242 Evolution and Adaptation 



only one-twelfth of an inch apart, and if the points are moved 

 nearer together, they give the sensation of only one point. 

 The inner surfaces of the second joints of the fingers can 

 only distinguish two points when they are one-sixth of an 

 inch apart. The innermost joints are less discriminating, 

 and are about equal in the power of discrimination to the tip 

 of the nose. The end of the big toe, the palm of the hand, 

 and the cheek discriminate only about one-fifth as well as do 

 the tips of the fingers. The back of the hand and the top 

 of the head distinguish only about one-fifteenth as well as 

 the finger-tips. The front of the thigh, near the knee, is 

 somewhat less sensitive than the back of the hand. On the 

 breast the points of the compasses must be separated by more 

 than an inch and a half in order to give two sensations. In 

 the middle of the back the points must be separated by two 

 and a half inches, or more, in order to give two separate 

 impressions. 



What is the meaning of these differences, Spencer asks. 

 If natural selection has brought about the result, then it must 

 be shown that " these degrees of endowment have advan- 

 taged the possessor to such an extent that not infrequently 

 life has been directly or indirectly preserved by it." He 

 asks if this, or anything approaching this, result could have 

 occurred. 



That the superior perceptiveness of the forefinger-tip 

 might have arisen through selection is admitted by Spencer, 

 but how could this have been the case, he asks, for the mid- 

 dle of the back, and for the face ? The tip of the nose has 

 three times more power of discrimination than the lower 

 part of the forehead. Why should the front of the thigh 

 near the knee be twice as perceptive as in the middle of 

 the thigh ; and why should the middle of the back and of 

 the neck and the middle of the forearm and of the thigh 

 stand at such low levels ? Is it possible, Spencer asks again, 

 that natural selection has determined these relations, and 



