HYPOTHESIS
FOR HUMAN BIPEDALISM
1. Freeing hands in defense of a terrestrial way of life (Darwin, 1871).
2. Brachiation responsible for the postcranial features we share with apes. Broken
down into three phases: gibbonlike, chimplike, and bipedal (Keith, 1923).
3. The avoidance of predators: extra vigilance in the savannas with frequent peering
over tall grass (Dart, 1926).
4. An aquatic phase of foraging and avoiding predators in water (Westenhofer, 1942;
Hardy, 1960; Morgan, 1972).
5. Bipedalism emerging from the need to carry babies, food, and other objects back to
base (Hewes, 1961; Isaac, 1978; Lovejoy, 1981).
6. Bipedalism explained by multiple factors (Napier, 1964).
7. “The upwardly mobile” hypothesis: small-bodied arboreal apes modifying their vertical
climbing to run bipedally along thick branches in the canopy (Tuttle, 1974).
8. Intimidation displays directed at other or same species (Westcott, 1976; Jablonski
and Chaplin, 1993).
9. “Two feet better than four” hypothesis: energetic efficiencies in bipedalism (Rodman
and McHenry, 1980).
10. Phallic display directed at females (Tanner, 1981).
11. A thermoregulatory theory whereby savanna dwellers rear up to keep cool
(Wheeler, 1984).
12. A “gimmick” spread by imitation then favored by selection (Dawkins, in litt).
13. Terrestrial squat-feeding in grassland (Jolly, 1970) and forest floor (Kingdon, 1997).