42 DARWINISM TO-DAY. 



of the fittest explains the origin of species as well as the 

 origin of adaptations, since all specific characters are really 

 adaptations. 



"But on the other hand, many naturalists think that there 

 are specific characters for which we cannot only see no 

 utility, but which are demonstrably of no use. A few illus- 

 trations will serve to make the matter clearer. Certain in- 

 sects are distinguished from each other in accordance with 

 whether they possess one or two bristles on the head. Here 

 is a character which appears to be constant, and which must 

 therefore be explained by any complete theory of the origin 

 of species. Can we imagine that the question of whether 

 the animal has one or two hairs should ever have been of 

 selective value? But if developed by natural selection, this 

 character must at some time have been a matter of life and 

 death. Again among snails, the shells commonly coil in 

 the same direction in the same species, this fact making the 

 direction of the coiling of the shell a specific character. But 

 clearly this is not a matter of selective value, since living 

 among the rest of the individuals will frequently be found 

 some with their shells coiled in the opposite direction. 

 Again, horses have small horny callosities on their feet. No 

 one has suggested any possible use for them, but neverthe- 

 less they are present on the feet of all the species of the horse 

 family. But the most curious fact is that while the horse has 

 them on all four feet, the ass has them on only two. Now, 

 upon the principle that utility is universal, it would be neces- 

 sary to claim, not only that the presence of four callosities 

 has been a matter of selective value in the horse, an ex- 

 tremely difficult thing to believe, but also that the presence 

 of only two instead of four has been of selective value in the 

 ass. This position approaches absurdity. Again, there are 

 molluscs characterised by special markings of the shell, 

 which markings are constant enough to be specific char- 

 acters, and must, of course, be included in any explanation 



