On The Origin of Species by Charles Darwin Chapter 14 Page 33

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 have no written pedigrees, we are forced to trace community of descent by resemblances of any kind.

Therefore, 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 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