Vertebral column, bipedalism and freedom of the hands

Summary

Abstract

The popular literature on human evolution suggests that trunk erectness and the appearance of permanent bipedalism implies a freeing of the hands. The hands, no longer having locomotor constraints, acquired a more important dexterity in the handling of objects, including tools. Observations of wild chimpanzees show, however, that tool use does not correlate with the acquisition of trunk erectness and permanent bipedalism. Manipulating objects can be done in a sitting position. But trunk erectness and the acquisition of permanent bipedalism will undoubtedly increase the capacity to handle objects, either standing still or moving.

Permanent bipedality in extinct species can only be studied using postcranial skeletons of Plio-Pleistocene or upper Miocene hominids. South Africa has one of the most important fossil hominid postcranial collections. The site of Sterkfontein alone has yielded three partial skeletons of australopithecines (Australopithecus africanus). That of Sts 14 has been employed to reconstruct the vertebral column and pelvis of ‘Lucy’ (AL288-1) (Australopithecus antiquus seu afarensis) from Ethiopia. Sts 14 was discovered in 1947 by R. Broom and J.T. Robinson, pioneers of palaeoanthropology in South Africa. South Africa has also yielded another type of Plio- Pleistocene hominid, Paranthropus robustus. They show many resemblances to Australopithecus africanus but have anatomical characteristics in their postcrania by which they differ. These characteristics might be useful in revealing a specific adaptation to their mode of locomotion and thus to their type of bipedality. Australopithecus africanus and paranthropines are divergent from other types of hominid from East Africa. These anatomical and functional differences must have implications for their behaviour, as in the way they handled or made objects and/or tools.

Some authors consider the South African paranthropines capable of making tools. This hypothesis, in particular, has been supported by the study of a phalanx of the thumb from Swartkrans. The discovery of phalanges of other hominids, like that reported for Orrorin tugenensis, makes it possible to review this conclusion.

Résumé

Classiquement, on trouve dans les ouvrages de vulgarisation que le redressement du corps et donc de l'apparition de la bipédie permanente ont entraîné une libération des mains. Ces mains n'ayant plus de contraintes locomotrices ont acquis une dextérité plus importante dans la manipulation d'objets et d'outils.