226 THE ORIGIN OF SPECIES 



treinely different; and as it has been used in classing 

 varieties whieii have undergone a certain, and some- 

 times a considerable amount of modification, may not 

 this same element of descent have been unconsciously 

 used in grouping species under genera, and genera under 

 higher groups, all under the so-called natural system ? I 

 believe it has been unconsciously used; and thus only 

 can I understand the several rules and guides which 

 have been followed by our best systematists. As we 

 bavo no written pedigrees, we are forced to trace com- 

 munity of descent by resemblances of any kind. Tliere- 

 fore we choose those characters which are the least likely 

 to have been modified, in* relation to the conditions of 

 life to which each species has been recently exposed. 

 Rudimentary structures on this view are as good as, or 

 even sometimes better than, other parts of the organiza- 

 tion. We care not how trifling a character may be — let 

 It be the mere inflection of the angle of the jaw, the 

 manner in which an insect's wing is folded, whether 

 the skin be covered by hair or feathers — if it prevail 

 throughout many and different species, especially those 

 having very different habits of life, it assumes high 

 value; for we can account for its presence in so many 

 forms with such different habits only by inheritance 

 from a common parent. We may err in this respect in 

 regard to single points of structure, but when several 

 characters, let them be ever so trifling, concur through- 

 out a large group of beings having different habits, we 

 may feel almost sure, on the theory of descent, that 

 these characters have been inherited from a common 

 ancestor; and we know that such aggregated characters 

 have especial value in classification. 



