Pe ee. PS 
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, Rytina, and Pallas’s 
cormorant on the Commander Islands, these 
animals were already restricted to this cireum- 
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 possible that the cormorant may always have been con- 
Jjined to this one spot, but this is probably not the case with the 
sea-com. 
