THEVOICEOFTHEDESERT 1Q2 



good are a disproportionately long tail and the ability to 

 make prodigious, unpredictably erratic leaps? 



There must be some reason, because in other faraway 

 deserts, those in Africa for instance, other creatures have 

 adapted themselves to the same "bipedal, saltatory exist- 

 ence." The African jumpers and the American are not 

 descended from a common ancestor w^ho just happened to 

 develop this habit. The African jerboa, even though he 

 looks and acts like a kangaroo rat and is also a rodent, is 

 not even very closely related. His analogue of the Aus- 

 tralian desert is also not descended from either of the other 

 two long tailed, short fore-legged desert creatures. Plainly 

 we are again faced with a case of "convei*gence" hke that 

 of the desert cacti of America and the desert Euphorbias 

 of Africa. Two different animals and two different plants 

 have independently developed useful tricks for living in 

 arid country. And the tricks are so similar that the two 

 organisms have come to look very much alike. But the 

 utility of the devices is evident in the case of the plants, 

 not nearly so evident in that of the animals. Still, though 

 no one is quite sure what the answer to the riddle is, a 

 guess seems pretty probable. 



Dipo can walk, or rather hobble, when he wants to. 

 When he is tranquil that is usually what he does. But 

 when he becomes excited or afraid, he begins to bound, 

 switching his tail in the air as he leaps. And it is the switch 

 of the long tail which makes his course unpredictable. 

 Whether or not he himself knows where he is going to land 

 is a question; certainly nobody else does. And that must 

 be a great help when being pursued by a predator, espe- 

 cially an owl or a hawk. When one of them swoops at a 

 Dipo, the Dipo usually turns out to be somewhere else. 



