[Acquisition of human bipedal gait from the viewpoint of the aquatic ape theory].

We are convinced that human bipedalism is better accounted for by the Aquatic Ape Theory than by the hypotheses, now commonly accepted, that the vertical gait is part of an adaptation for life in the savannahs. The advantages of the upright gait are easily understood by the versatility of this locomotion in a semi-aquatic mode of life. Early hominid bipedalism cannot be described as an ideal adaptation for one isolated form of locomotion, since human bipedalism covers a wide range of locomoter behaviours such as diving, swimming, wading, climbing trees and rocks, and moving on land. This locomotor versatility, however, should not be confused with theories that consider humans and their ancestors as "primitive" or "unspecialized" creatures. The pronounced swimming and diving abilities of humans--and the features that make these abilities possible--represents the most striking element of our species locomotor spectrum in comparison with highly specialized "savannah primates". On the one hand baboons and geladas are clearly better-adapted to savannah conditions than humans are, if the acquisitions of modern technology are not taken into consideration. To these adaptations belongs quadrupedalism, which is the most common and successful form of locomotion among terrestrial tetrapods. On the other hand, humans are in most respects much better swimmers and divers than nonhuman primates even without technological help. The only satisfying explanation for these different adaptations of humans and nonhuman primates is provided by the Aquatic Ape Theory. It is the only model of humans evolution that accounts for the numerous examples of convergent features between people and other vertebrates and the only model that explains these convergences in connection with a well-defined ecological niche.