Darwin (1871)
Classification: Forelimb pre-emption (carrying models)
Mnemonic: "Freeing of the hands"
Specific Model: General Carrying (Details Unspecified) 
Original Proponent(s): Original Proponent(s): Darwin 1871:50-54. (Also attributed to Hooton 1945)    
Assessment: Popularity Ranking: 1st out of 9 categories (86% of texts)
Simple Evaluation: #20 (=4) /42 (57%)
Detailed Evaluation: #12 (=5) /42 (57%)
Basic Summary:

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 20th 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.

1.1 Survival Value Good 6:  The general carrying models all provide very strong arguments for selection. Carrying things (infants, food, or weapons) clearly has potentially strong selective advantages.    
1.2 Sexual Selection Fair 5: Although some carrying models presume some sexual discrimination, most postulate equal roles of carrying for males and females. This therefore cannot be judged as a vehicle for strong sexual selection.    
1.3 Not Teleological Poor 3: Modern humans today can carry things easily, mainly because their anatomy has become adapted to an efficient kind of bipedalism. It is not clear that this behaviour would have been so easy and therefore advantageous in intermediate forms.    
2.1 Improved Food Acquisition Fair: 6: Some carrying models are stronger than others on this but the overall average would have to be slightly better than fair as carrying would enable greater procurement of food.    
2.2 Accounts for Predation Fair 6: These models tend to suggest that one of the things likely to be carried are weapons. This is clearly a rather good answer to the predation question, because it is clearly the main answer modern humans have to the same problem today.    
2.3 Why Apes are not Bipedal Fair 4: Most of the arguments in favour of ‘carrying models’ are not very explicit in describing why the same kind of pressures did not occur in other ape lineages    
2.4 Extant Analogues Fair 6: Most extant apes can be seen to exhibit bipedalism whilst carrying objects that are too large, or numerous, to carry on three limbs or four, albeit rarely. But often too, they are observed carrying items tripodally or orally, whilst moving quadrupedally.    
2.5 Applies to Both Sexes Good 9: Although many specific sub-models in this category are quite explicit in suggesting sex-based roles for the kind of carrying being proposed. It is suggested that overall ‘carrying’ as a general concept works well for both sexes.    
3.1 Hominid Anomalies Fair 4: As far as can be seen in the literature, none of the carrying models offer this model as any kind of explanation for the rather peculiar differences between Australopithecus and Homo in lower limb anatomy.    
3.2 Fits Paleoecological Record Fair 5: Some of the carrying models have been traditionally based on the long held asumption of a shift in habitat from forested towards more open savannah butothers have not.    
3.3 Precursor to Strider and knuckle Walker Fair 4: Carrying models, for the most-part, appear to assume a chimp-like LCA. It was out lineage, that started needing to carry things more, that emerged from quadrupedalism.    
4.1 Extended Explanatory Power Fair 6: Many of the carrying models were originally proposed merely as part of a bigger model of early human evolution. Lovejoy’s “Provisioning Model” in particular (see below) is particularly comprehensive in attempting to explain several of the ape-human differences at one fell swoop.    
4.2 Complimentary Good 7: Many of the models, if not all, assume that carrying played some part in fixing the switch to bipedal locomotion to some degree and therefore this can be said to be one of the most compatible models known.    
4.3 Falsifiable or Testable Poor 0 : Few, if any, of the proponents of carrying models have attempted to make testable predictions.    
References Dart, Raymond A; Craig, Dennis (1959). Adventures with the Missing Link. The Institution Press (Philadelphia).
Darwin, Charles (1879). The Descent of Man and Selection in Relation to Sex. 2 Vols. Murray (London).
Graslund, Bo (2005). Early Humans and their World. Routeledge (London).
Hewes, Gordon W (1961). Food Transport and the Origin of Hominid Bipedalism. American Anthropologist Vol:63 Pages:687-710.
Hooton EA. (1945) "Young Man, You are Normal" Findings from a study of students. New York: GM Putnam's & Sons.
Hunt, Kevin. The Evolution of human bipedality: ecology and functional morphology. Journal of Human Evolution 26:183-202, (1994).
Jolly, Clifford J (1970). The Seed-Eaters: A New Model of Hominoid Differentiation Based on a Baboon Analogy. Man Vol:5 Pages:5-26.