THE INADEQUACY OF "NATURAL SELECTION:' 801 



Why is this ? Advantage might occasionally be derived if the 

 back of the hand could tell us more than it does about the shapes 

 of the surfaces touched. Why should the thigh near the knee be 

 twice as perceptive as the middle of the thigh ? And, last of all, 

 why should the middle of the forearm, middle of the thigh, middle 

 of the back of the neck, and middle of the back, all stand on the 

 lowest level, as having but one thirtieth of the perceptive power 

 which the tip of the forefinger has ? To prove that these differ- 

 ences have arisen by natural selection, it has to be shown that such 

 small variation in one of the parts as might occur in a generation 

 — say one tenth extra amount — has yielded an appreciably greater 

 power of self-preservation, and that those inheriting it have con- 

 tinued to be so far advantaged as to multiply more than those 

 who, in other respects equal, were less endowed with this trait. 

 Does any one think he can show this ? 



But if this distribution of tactual perceptiveness can not be 

 explained by survival of the fittest, how can it be explained ? The 

 reply is that, if there has been in operation a cause which it is 

 now the fashion among biologists to ignore or deny, these various 

 differences are at once accounted for. This cause is the inherit- 

 ance of acquired characters. As a preliminary to setting forth 

 the argument showing this, I have made some experiments. 



It is a current belief that the fingers of the blind, more prac- 

 ticed in tactual exploration than the fingers of those who can see, 

 acquire greater discriminativeness : especially the fingers of those 

 blind who have been taught to read from raised letters. Not 

 wishing to trust to this current belief, I recently tested two 

 youths, one of fifteen and the other younger, at the School for the 

 Blind in Upper Avenue Road, and found the belief to be correct. 

 Instead of being unable to distinguish between points of the com- 

 passes until they were opened to one twelfth of an inch apart, I 

 found that both of them could distinguish between points when 

 only one fourteenth of an inch apart. They had thick and coarse 

 skins ; and doubtless, had this intervening obstacle so produced 

 been less, the discriminative power would have been greater. It 

 afterward occurred to me that a better test would be furnished by 

 those whose finger-ends are exercised in tactual perceptions, not' 

 occasionally, as by the blind in reading, but all day long in pur- 

 suit of their occupations. The facts answered expectation. Two 

 skilled compositors, on whom I experimented, were both able to 

 distinguish between points when they were only one seventeenth 

 of an inch apart. Thus we have clear proof that constant exercise 

 of the tactual nervous structures leads to further development.* 



* Let me here note in passing a highly significant implication. The development of 

 nervous structures which in such cases takes place, can not be limited to the finger-ends. 

 TOL. XLH. — 56 



