Climbing, brachiation, and terrestrial quadrupedalism: Historical precursors of hominid bipedalism

Abstract

The vertical-climbing account of the evolution of locomotor behavior and morphology in hominid ancestry is reexamined in light of recent behavioral, anatomical, and paleontological findings and a more firmly established phylogeny for the living apes. The behavioral record shows that African apes, when arboreal, are good vertical climbers, and that locomotion during traveling best separates the living apes into brachiators (gibbons), scrambling/ climbing/brachiators (orangutans), and terrestrial quadrupeds (gorillas and chimpanzees). The paleontological record documents frequent climbing as an ancestral catarrhine ability, while a reassessment of the morphology of the torso and forelimb in living apes and Atelini suggests that their shared unique morphological pattern is best explained by brachiation and forelimb suspensory positional behavior. Further, evidence from the hand and foot points to a terrestrial quadrupedal phase in hominoid evolution prior to the adoption of bipedalism. The evolution of positional behavior from early hominoids to hominids appears to have begun with an arboreal quadrupedal-climbing phase and proceeded though an orthograde, brachiating, forelimb-suspensory phase, which was in turn followed by arboreal and terrestrial quadrupedal phases prior to the advent of hominid bipedality. The thesis that protohominids climbed down from the trees to become terrestrial bipeds needs to be reexamined in light of a potentially long history of terrestriality in the ancestral protohominid.

Origin of human bipedalism: The knuckle-walking hypothesis revisited

“…The focus has shifted instead to whether bipedalism was preceded by exclusively or nearly exclusively climbing and suspensory behaviors (Tuttle, 1969aStern, 1975), including vertical climbing (Prost, 1980;Fleagle et al, 1981;Stern and Susman, 1981;Ishida et al, 1985;Senut, 1988), in a large-bodied ape, or whether the ancestral condition included a significant terrestrial (Gebo, 1996;Sarmiento, 1998), possibly knuckle-walking component (Washburn, 1967;Corruccini, 1978;Shea and Inouye, 1993;Begun, 1993aBegun, , 1994Strait, 2000, 2001d). Arguments for suspensory/ climbing ancestors ( Fig.…”

“…1), on the other hand, cite numerous terrestrial traits shared between hominins and African apes to the exclusion of Asian apes (Sarmiento, 1994(Sarmiento, , 1988Gebo, 1992Gebo, , 1996. A few researchers have suggested that palmigrade terrestriality preceded bipedalism (Delmas, 1972;Hotton et al, 1984).…”

The Dart-Throwing Motion of the Wrist: Is It Unique to Humans?

“…41 This close-packing mechanism in the African apes may be aided by the near 100% occurrence of early fusion of the os centrale to the scaphoid in Pan and Gorilla (a characteristic shared with hominins). 42,[44][45][46][47][48][49][50][51] The os centrale portion of the scaphoid forms a broad, stable articular surface for the trapezium and trapezoid. In wrist extension, the os centrale becomes lodged within an embrasure formed by the capitate head and the trapezoid, 42,44,50 and scaphoid-centrale fusion might provide increased resistance to extension moments at the midcarpal joint.…”

Functional morphology of the ankle and the likelihood of climbing in early hominins

“…Although early hominins were not chimpanzees per se, some researchers have argued that the last common ancestor of humans and chimpanzees was probably quite chimpanzee-like (20), including in its locomotion (21,22). Furthermore, when the prospects of climbing in hominins are discussed in the paleoanthropological literature, the model that is used is often a chimpanzee one (e.g., refs.…”