The Energetic Paradox of Human Running and Hominid Evolution ' by

THE FEATURE THAT DIFFERENTIATES HOMINIDS from other primates is not large brain size, but the set of characters associated with erect bipedal posture and a striding ait. Long before the rapid increase in relative brain size that took place during the Pleistocene, early australopithecines possessed the postcranial morphology of an erect, striding biped (Lovejoy, Heiple, and Burstein 1973). Evidence for the bipedal gait of early hominids is provided by the morphology of the 3.5-millionyear-old postcranial material from the Hadar Formation of Ethiopia (Johanson, Taieb, and Coppens 1982, Lovejoy, Johanson, and Coppens 1982), early Pleistocene material from eastern and southern Africa (Preuschoft 1971), and the Pliocene trackways (3.6 to 3.8 million years old) discovered at Laetoli in northern Tanzania (Leakey and Hay 1979, White 1980). Together these suggest that early australopithecines were relatively small-brained creatures, possessing structural adaptations for upright walking and running that in a broad sense are remarkably similar to those of modern man. The aspects of locomotion that unite the hominids as a group are also uniquely hominid in character and distinctly peculiar for mammals. Consequently, the study of human locomotion, in addition to explaining much of the biology of the one remaining hominid, may prove to be one of the more powerful inductive approaches to the study of hominid evolution. The energetic ost of transport (oxygen consumption per unit body mass per unit distance traveled) for running humans is relatively high in comparison with that for other mammals and running birds. Early comparative studies showed that a mam-