494 DE. ALFEEB E. WALLACE OK 



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 o£ 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 characters may have been 

 produced in some such manner as the following. If some iiseless 

 character appears as a variation in some individuals of excep- 

 tional vigour, it may increase by interbreeding, and its repeated 

 production being perhaps favoured by some local conditions, it 

 may come to form a marked local variety. Now, if the conditions 

 become unfavourable to the species in the area occupied by the 

 type, this may in course of time become extinct, and the variety 

 distinguished by the altogether useless character will remain as 

 the only representative of the species. It may be admitted that 

 such a mode of origin of a non-utilitarian specific character is 

 conceivable, but whether it ever actually occurs in nature may 

 be doubted; while if it does occur, it must be owing to so rare a 

 combination of circumstances that it can produce no such general 

 prevalence of useless specific characters as is claimed by the 

 advocates of that theory*. 



In order to ascertain whether the immediate antecedent to 

 such a mode of species-formation as is suggested is at all common, 

 and thinking that British flowering plants offer the best materials 

 for its detection, I put the case to two experienced British 



* If, however, the variation is preserved because it occurs in exceptionally 

 ■vigorous individuals, it is correlated vrith a character which is useful. 



