228 THE LAW. 



[Duration of Species.] 



In reasoning on the causes which have led to the ex- 

 tinction of races, we must not lose sight of the speculation, 

 that species, like individuals, may have had a limit of 

 duration assigned to them from the beginning, and that 

 this limit may be attained even when all extraneous causes 

 remain quiescent and stationary. " Attempts have been 

 made," says Professor Owen, "to account for the extinction 

 of the race of northern elephants (the mammoth of Siberia) 

 by alterations in the climate of their hemisphere, or by 

 violent geological catastrophes, and the like extraneous 

 physical causes. When we seek to apply the same hypo- 

 thesis to explain the apparently contemporaneous extinc- 

 tion of the gigantic leaf-eating megatherium of South 

 America, the geological phenomena of that continent ap- 

 pear to negative the occurrence of such destructive changes. 

 Our comparatively brief experience of the progress and 

 duration of species within the historical period is surely in- 

 sufficient to justify, in every case of extinction, the verdict 

 of violent death. With regard to many of the larger mam- 

 malia, especially those that have passed away from the 

 American and Australian continents, the absence of suffi- 

 cient signs of extrinsic extirpating change or convulsion 

 makes it almost as reasonable to speculate with Brocchi 

 on the possibility that species, like individuals, may have 

 had the cause of their death inherent in their original con- 

 stitution, independently of changes in the external world ; 

 and that the term of their existence, or the period of ex- 

 haustion of the prolific force, may have been ordained from 

 the commencement of each species." We can readily ac- 

 count for the annihilation of races by the submergence and 

 elevation of land, by alterations in the aerial and oceanic 



