Chap. XIII. 
CLASSIFICATION, 
425 
As descent has uniyersally been used in classing to¬ 
gether the individuals of the same species, though the 
males and females and larvsc are sometimes extremely 
different; and as it has been used in classing varieties 
which have undergone a certain, and sometimes a con¬ 
siderable amount of modification, may not this same 
element of descent have been unconsciously used in 
grouping species under genera, and genera under higher 
groups, though in these cases the modification has been 
greater in degree, and has taken a longer time to com¬ 
plete ? I believe it has thus been unconsciously used; 
and only thus can I understand the several rules and 
guides which have been followed by our best system- 
atists. We have no written pedigrees; we have to 
make out community of descent by resemblances of any 
kind. Therefore we choose those characters which, as 
far as we can judge, are the least likely to have been 
modified in relation to the conditions of life to which 
each species has been recently exposed. Eudimentary 
structures on this view are as good as, or even some¬ 
times better than, other parts of the organisation. 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 its 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, occur together throughout 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. 
