384 ON THE ORIGIN OF SPECIES 



isolated region, have in all probability descended from 

 the same parents. 



We can understand, on these views, the very im- 

 portant distinction between real affinities and analogical 

 or adaptive resemblances. Lamarck first called atten- 

 tion to this distinction, and he has been ably followed 

 by Macleay and others. The resemblance, in the shape 

 of the body and in the fin-like anterior limbs, between 

 the dugong, which is a pachydermatous animal, and 

 the whale, and between both these mammals and fishes, 

 is analogical. Amongst insects there are innumerable 

 instances : thus Linnaeus, misled by external appear- 

 ances, actually classed an homopterous insect as a 

 moth. We see something of the same kind even in 

 our domestic varieties, as in the thickened stems of the 

 common and Swedish turnip. The resemblance of the 

 greyhound and racehorse is hardly more fanciful than 

 the analogies which have been drawn by some authors 

 between very distinct animals. On my view of char- 

 acters being of real importance for classification, only 

 in so far as they reveal descent, we can clearly under- 

 stand why analogical or adaptive character, although 

 of the utmost importance to the welfare of the being, 

 are almost valueless to the systematist. For animals, 

 belonging to two most distinct lines of descent, may 

 readily become adapted to similar conditions, and thus 

 assume a close external resemblance ; but such re- 

 semblances will not reveal — will rather tend to conceal 

 their blood-relationship to their proper lines of descent. 

 We can also understand the apparent paradox, that 

 the very same characters are analogical when one class 

 or order is compared with another, but give true 

 affinities when the members of the same class or order 

 are compared one with another : thus the shape of the 

 body and fin-like limbs are only analogical when whales 

 are compared with fishes, being adaptations in both 

 classes for swimming through the water ; but the shape 

 of the body and fin-like limbs serve as characters 

 exhibiting true affinity between the several members 

 of the whale family ; for these cetaceans agree in so 



