220 EVOLUTION OF TO-DAY, 



that many of the peculiarities which distinguish 

 species from each other are useless. There exist 

 what are called morphological species, by which 

 term is meant species whose distinction rests upon 

 some slight difference in shape, size, or color 

 differences which can be of no use to the individual. 

 As instances of the point may be mentioned the 

 length of the ears and tails of different rabbits and 

 mice ; the complex folds in the enamel of teeth ; 

 the peculiar sculpturing of the hair of different ani- 

 mals ; the extremely slight differences in the mark- 

 ings of two species, so slight, frequently, as to be 

 distinguishable only with the closest scrutiny ; the 

 differences in the veining of the wings of different 

 butterflies, etc. All such instances are features dis- 

 tinguishing species, and must, of course, be accounted 

 for in a complete explanation of the origin of 

 species ; but, since they are of no use to their pos- 

 sessor, they cannot, by any means, come under the 

 influence of natural selection. 



In answer to such suggestions it is claimed that 

 we never can say with positiveness that a given feat- 

 ure is of no use to its possessor. We are too in- 

 completely acquainted with the lives of animals ; 

 and to say that a given feature is of no use is 

 usually an assumption based on ignorance. This 

 is doubtless true ; for there are certainly many char- 

 acteristics which have uses that we do not yet 

 know. But, on the other hand, it must be remem- 

 bered what the natural-selection theory means by a 

 useful structure. In order that a peculiarity should 

 be preserved by natural selection, it must be of so 



