which the trunk is held horizontally and a 

 long tail is used as a counterbalance. 

 Bipedal dinosaurs walked with a similar 

 body posture, and their descendants, the 

 birds, still maintain a horizontal torso 

 (penguins are the only exception), com- 

 pensating for the loss of the bony tail by 

 pivoting the body over the knees. But hu- 

 mans, evolving as we did from African 

 apes that had aheady lost the tail and de- 

 veloped an upright torso, inherited a 

 unique set of design constraints and adap- 

 tations that made the "normal" mode of 

 vertebrate bipedality impossible. 



The great South American radiation of 

 primates produced no upright ape, which 

 is surprising since a remarkable example 

 of convergence exists between the Asian 

 gibbon, the most primitive of the living 



apes, and the South American brachiating 

 spider monkey, although the latter differs 

 in possessing a long, prehensile tail. I sus- 

 pect that the South American monkeys 

 never experienced an apelike radiation be- 

 cause the role of a terrestrial, at least par- 

 tially bipedal herbivore was already taken 

 up by the endemic ground sloths. 



The uniqueness of the human ecomorph 

 is often a source of pride. However, with 

 all the problems facing the planet today — 

 so many seemingly a result of the spread 

 of civilization — we might perhaps be wise 

 to hope that if the human species ever does 

 succeed in doing itself in, our particular 

 ecomorphological type will not reemerge 

 any time soon. The worid might survive a 

 reappearance of the sabertooths, but could 

 it take another round of us? 



'^:n-^i^m^-^ 



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