xviii THE PROBLEM OF UTILITY 395 



conolusive proof of the non-heredity of acquired char- 

 acters. He declared that this case " definitely and con- 

 clusively" overturns the assumption of natural selection 

 having acted in this case, but he omitted to state that it 

 also (if his interpretation is correct) definitely and con- 

 clusively overturns the assumption of the heredity of 

 acquired characters, which in the same volume he has 

 elaborately discussed. 



The only other case of much importance is that of 

 changes of colour said to be directly caused by changes of 

 climate, and especially by darkness in cave-animals. In 

 this latter case it is declared by Mr. Romanes that the 

 loss of colour cannot be of any use and cannot have been 

 caused by natural selection. It is, therefore, an example 

 of a useless character occurring in all the individuals of 

 many unconnected species. In the case of the Proteus 

 however, it is stated that when subjected to the action of 

 light in confinement, the skin becomes dark, showing that 

 the character is in some degree an individual one, due 

 probably to deficiency of nutrition or, partially, to the need 

 of light for the secretion of the pigment. The whiteness 

 is here not a specific character. And if, in other cases, 

 it is permanent and specific, it may have had a very obvious 

 use in the early stages of the modification of a cave-fauna. 

 For if any animals were isolated in caverns which were 

 not totally dark, the light tints would be important as 

 recognition marks, enabling the sexes to find each other ; 

 and when, at a later period, the species spread into the 

 parts which were totally dark, there would be no cause 

 leading to a return of the positive colour, especially as all 

 cave-animals subjected to total darkness must at first 

 have been in great danger of extinction from deficiency of 

 food, and there would thus be no surplus nourishment 

 available for the production of pigments. 



Several biological friends with whom I have discussed 

 this question, while agreeing that the majority of specific 

 characters are useful, have suggested that useless char- 

 acters may have been produced in some such manner as 

 the following. If some useless character appears as a 



