140 THE THEORY OF EVOLUTION 



todons and the true elephants lived together all over 

 North America, but only the mastodons entered 

 South America. A possible explanation of this may 

 be that the species of elephants were cold-country 

 animals which had come in from the north and were 

 unable to cross the Tropics, but no such considera- 

 tions will apply to the Siberian rhinoceros and mam- 

 moth. Both were well protected against the cold 

 and both extended their range in the Pleistocene 

 from southwestern France to Kamchatka; the mam- 

 moth passed over to Alaska and crossed North 

 America to New England, but the rhinoceros has 

 never been found on the American side. Deer mi- 

 grated repeatedly from the Old World to the New, 

 but the giraffes, which were once very numerous and 

 varied in all the Mediterranean lands, did not accom- 

 pany them. Wolves, foxes, cats, bears migrated back 

 and forth, but America never had any hyenas or 

 civets and the raccoon family has always been Amer- 

 ican, though not quite exclusively so. The large, 

 spotted cats, called jaguars, do not extend north of 

 Texas or south of the Argentine Republic, yet the 

 very nearly allied pumas range from Pennsylvania 

 far into Patagonia. These are closely allied species 

 and yet their adaptability to climate is very differ- 

 ent. Deer and antelopes both invaded South Amer- 

 ica, presumably together, yet the deer maintained 

 themselves, while the antelopes failed to do so. 

 Then, too, there is much mystery about the extinc- 

 tion of species and larger groups; in a general way 



