The first popular idea on bipedal origins, one which Darwin described in ‘Descent of Man’ 1871:52, that it was to “free the hands”, seems a natural one to start with, and a natural one for anthropologists to have come to. A clear benefit of our bipedalism is indeed that our hands appear to have been ‘freed’ to carry things, when upper limb function is compared to most quadrupedal animals.

This has some obvious evolutionary advantages that would have clearly benefited hominin ancestors…

·         Hands ‘freed’ of the burden of locomotion (carrying body weight, as in quadrupedal terrestrial animals, or climbing as in arboreals) allowed “their delicate use” (Darwin 1979:52) to be put to more intellectual utility.

·         Two arms are able to carry greater loads whilst moving bipedally than would be the case whilst moving quadrupedally or, as is often seen in the case of African apes, tripodally (Hewes 1961.)

·         The better use of weapons, such as stones, spears and clubs, which was conferred onto bipeds, would have made them better able to defend themselves. (Dart 1959.)

In Darwin’s day, it was widely believed that the large brain (and also early aspects of human culture) preceded bipedality, which added to the attractiveness of this kind of model. However fossil evidence of small-brained bipedal hominids, which began to emerge early in the 20^th century, (e.g. Dart 1925) <CitationKey Id=221230 /CitationKey>corrected this view and hence made models involving forearm pre-emption less attractive.

The idea of the benefit of freeing the hands has persisted, however, and several more specific models have been proposed, varying in complexity, the main sex involved and the actual use to which the hands were employed.

Generally, it is the rather elegant positive feedback loop, which these carrying models provide, which makes them so compelling. In fact Jolly (1970) described them as ‘feedback models’, describing their strengths…

“Bipedalism frees the forelimb to make and use artefacts; regular use of tools and weapons permits (or causes) reduction of the anterior teeth by taking over their functions; the elaboration of material culture and associated learning is correlated with a cerebral reorganization of which increase in relative cranial capacity is one aspect. Bipedalism is needed to permit handling of the relatively helpless young through the long period of cultural conditioning and so on.” Jolly (1970:5)

… and weaknesses in such terms…

“Preoccupied with the apparent elegance of the feedback model, we tend to forget that to demonstrate the mutual relationship between the elements is not to account for their origin, and hence does not account for why the hominids [hominins] became differentiated from the pongids [hominids]. From their very circularity, feedback models cannot explain their own beginnings, except by tautology, which is no explanation at all.

In fact the more closely the elements of the hominid complex are shown to interlock, the more difficult it becomes to say what was responsible for setting the feedback spiral in motion, and for accumulating the elements in the cycle in the first place. Most authors seem to avoid the problem of origins and causes altogether (beyond vague references to 'open country' life), or fall back upon reasoning that tends to be tautological and often also illogical.” Jolly (1970:5)

A few general problems with this idea have been articulated in the literature. Notably:

·         Compared to other primates, it has been argued (e.g. Gräslund 2005:66) that it is not so much that bipedalism has ‘freed’ the hands, as much as it has ‘enslaved the feet’. Chimpanzees, for example, are well known to manipulate objects such as food with all four limbs, whilst sitting down, and are able to carry things with their hind limbs, whilst climbing trees.

·         Although it is easy to see how freeing’ the hands might have been selected for once a trend towards bipedality had begun, it is less clear to see how that trend might have been started in the first place. This point is made by Hewes (1961) when he suggests that “cause and effect are blurred in many presentations” (p693.)
Specifically, extant apes have rarely been observed using their forearms for carrying items. In Hunt’s (1994:185) study, carrying (specifically of infants) amounted to only 1% of the already relatively rare (around 3% of time) bipedal behaviour. It is difficult, therefore, to postulate scenarios whereby carrying could have acted as a behavioural driver for this form of locomotion.