Before bipedality

Abstract

KEY WORDS human evolution • bipedality • primate locomotion • primate anatomy. This paper attempts to place into perspective information, to a large extent gathered by others, about the locomotor behavior of man's ancestors before the time when that behavior became characterized by an unnatural degree of terrestrial bipedalily. Suggestions that the human lineage might have avoided a decidedly arboreal stage with adaptations for antipronograde behavior are challenged. Comparison of the anatomy of modern and fossil man to living antipronograde primates reveals numerous similarities to the orangutan, some to prehensile-tailed cebids, and very little indeed to the African apes or gibbon. It is concluded that before becoming bipedal, the human ancestor was predominantly adapted for life in the trees, employing its forclimbs much as docs the living orangutan, and its hindlimbs in a somewhat more pronograde quadrupedal manner than docs Pongo. The speculation is offered that the upper limbs of this animal may have been so long and so completely adapted to antipronograde activities that the only reasonable choice upon descent to the ground was to free them from locomotor function.