CHAP. xxii. LONGEVITY OF SPECIES IN MAMMALIA. 441 



We usually know nothing of the geographical varieties of the 

 post-pliocene and pliocene species, least of all, those successive 

 changes of form which they must have undergone in the pre- 

 glacial epoch between the upper miocene and post-pliocene 

 eras. Such being the poverty of our palseontological data, 

 we cannot wonder that osteologists are at variance as to 

 whether certain remains found in caverns are of the same 

 species as those now living ; whether, for example, the Talpa 

 fossilis is really the common mole, the Meles morreni the 

 common badger, Lutra antiqua the otter of Europe, Sciurus 

 priscus the squirrel, Arctomys primigenia the marmot, 

 Myoxus fossilis the dormouse, Schmerling's Felix Engihou- 

 lensis the European lynx, or whether Ursus spelceus and 

 Ursus priscus are not extinct races of the living brown bear 

 ( Ursus arctos). t 



If at some future period all the above-mentioned species 

 should be united with their allied congeners, it cannot fail to 

 enlarge our conception of the modifications which a species 

 is capable of undergoing in the course of time, although the 

 same form may appear absolutely immutable within the 

 narrow range of our experience. 



Longevity of Species in the Mammalia. 



In the < Principles of Geology,' in 1833,* I stated that the 

 longevity of species in the class mollusca exceeded that in 

 the mammalia. It has been since found that this generalisa 

 tion can be carried much farther, and that, in fact, the law 

 which governs the changes in organic beings is such, that the 

 lower their place in a graduated scale, or the simpler their 

 structure, the more persistent are they in form and organisa 

 tion. I soon became aware of the force of this rule in 

 the class mollusca, when I first attempted to calculate the 



* 1st edit., vol. iii. pp. 48 and 140. 



