THE VOICE OF THE DESERT 



130 



what I have described. North of the canyon his relative 

 the kaibab squirrel with a pure white tail takes over com- 

 pletely. As usual there is the dispute — meaningless since 

 evolution has been understood — whether the two are to be 

 regarded as separate species or merely as separate varie- 

 ties. But if the kaibab is not yet a separate species it is in 

 the process of becoming one. Its race and that of the abert 

 are separated by the great gash of the Canyon, running 

 east and west, and they have been so separated ever since 

 the Colorado River got well started on the cutting job 

 which began a few million years ago. Perhaps, if man 

 were to carry a few of each into the territory of the other 

 they would interbreed and possibly eliminate the distinc- 

 tion. But unless man does so, or unless squirrels learn how 

 to travel and to carry their food supplies with them, the 

 aberts and the kaibabs may very well go on getting more 

 and more different from one another just as races of men 

 similarly isolated develop racial characteristics. 



Workers in several different sciences are becoming 

 more and more convinced that both the north temperate 

 and the arctic climates are growing milder. A minor evi- 

 dence is the way in which certain animals and birds — no- 

 tably the 'possum, the turkey buzzard and the cardinal- 

 are extending their range into New England. Here in the 

 Southwest the same sort of thing is happening. The coati, 

 comic relative of the raccoon, which used to belong only in 

 Mexico and southward, is becoming increasingly common 

 in southern Arizona. Even more striking is the case of the 

 armadillo. Formerly known in the United States only 

 from Texas and the Mexican frontier, it has spread dur- 



