WHY DO ANIMALS BECOME EXTINCT? 225 



man even existed, so that, while he is responsi- 

 ble for the great changes that have taken place 

 in the world's flora and fauna during recent 

 times, his influence, as a whole, has been insig- 

 nificant. Thus, while man exterminated the 

 great northern sea-cow, Tlytina, and Pallas's 

 cormorant on the Commander Islands, these 

 animals were already restricted to this circum- 

 scribed area* by natural causes, so that man 

 but finished what nature had begun. The ex- 

 termination of the great auk in European 

 waters was somewhat similar. There is, how- 

 ever, this unfortunate difference between ex- 

 termination wrought by man and that brought 

 about by natural causes : the extermination of 

 species by nature is ordinarily slow, and the 

 place of one is taken by another, while the de- 

 struction wrought by man is rapid, and the gaps 

 he creates remain unfilled. 



Not so very long ago it was customary to 

 account for changes in the past life of the 

 globe by earthquakes, volcanic outbursts, or 



* It is possib/e that the cormorant may always have been con- 

 Jined to this one spot, but this is probably not the case with the 

 sea-cow. 



