Page - 453 - in The Origin of Species

CLASSIFICATION 453 those parts of the structure which determined the habits of life, and the general place of each being in the economy of nature, would be of very high importance in classification. Nothing can be more false. No one regards the external similarity of a mouse to a shrew, of a dugong to a whale, of a whale to a fish, as of any importance. These resemblances, though so intimately connected with the whole life of the being, are ranked as merely "adaptive or analogical charac- ters ;" but to the consideration of these resemblances we shall recur. It may even be given as a general rule, that the less any part of the organisation is concerned with special habits, the more important it becomes for classification. As an instance: Owen, in speaking of the dugong, says, "The generative organs, being those which are most remotely re- lated to the habits and food of an animal, I have always regarded as affording very clear indications of its true affinities. We are least likely in the modifications of these organs to mistake a merely adaptive for an essential char- acter." With plants how remarkable it is that the organs of vegetation, on which their nutrition and life depend, are of little signification ; whereas the organs of reproduction, with their product the seed and embryo, are of paramount importance ! So again in formerly discussing certain mor- phological characters which are not functionally important, we have seen that they are often of the highest service in classification. This depends on their constancy throughout many allied groups ; and their constancy chiefly depends on any slight deviations not having been preserved and accumu- lated by natural selection, which acts only on serviceable characters. That the mere physiological importance of an organ does not determine its classificatory value, is almost proved by the fact, that in allied groups, in which the same organ, as we have every reason to suppose, has nearly the same physiolog- ical value, its classificatory value is widely different. Xo naturalist can have worked long at any group without being struck with this fact; and it has been fully acknowledged in the writings of almost every author. It will suffice to quote the highest authority, Robert Brown, who. in speaking of certain organs in the Proteacea;, says their generic impor-