Bipedalism.

Reasons why mammalian bipedalism is so rare. Problems encountered by the larger arboreal mammals when they descend to ground level. Reasons for believing that hominid ancestors were never knuckle-walkers. Primate models which combine arboreal life with incipient bipedalism. Disadvantages of mammalian bipedalism. Critique of some of the savannah-based theories on the origins of human bipedalism.