224 ANIMALS OF THE PAST 
that in some portions of their range they may 4 
have been extirpated by a change in food-sup- — 
ply, due in turn toa change in climate, it seems — 
preposterous to claim that there was not at all 
times, somewhere in this vast expanse of terri- 
tory, a climate mild enough and a food-supply 
large enough for the support of even these 
huge, sluggish creatures. We may evoke the 
aid of primitive man to account for the disap-_ 
pearance of this race of giants, and we know 
that the two were coeval in Patagonia, where — 
the sloths seem to have played the rdle of do- — 
mesticated animals, but again it seems incred- — 
ible that early man, with his flint-tipped spears 4 
and arrows, should have been able to slay even a 
such slow beasts as these to the very last indi- 
vidual. 
Of course, in modern times man has directly a 
exterminated many animals, while by the in- © 
PS 
troduction of dogs, cats, pigs, and goats he has - 
indirectly not only thinned the ranks of ani- 
mals, but destroyed plant life on an enormous __ 
scale. But in the past man’s capabilities for | 
harm were infinitely less than now, while of — 
course the greatest changes took place before ; 
