Hewes (1961)
Classification: Forelimb pre-emption (carrying models)
Mnemonic: "Freeing of the hands"
Specific Model: Food Transport and the Origin of Hominid Bipedalism.
Original Proponent(s): Hewes (1961)    
Assessment: Popularity Ranking: 1st out of 9 broad categories (86% of texts)
Simple Evaluation: #35 /42 (49%)
Detailed Evaluation: #17 (=4) /42 (56%)
Basic Summary:

Substantial paper <CitationKey Id=5071230 /CitationKey>proposing that food carrying would have provided sufficient selective advantage to the earliest bipeds.


His thesis began with a demonstration that bipedalism is nothing particularly unusual, being the norm in the class Aves and in many Mesozoic reptilian forms, as well as being well known in many primates.

Hewes then makes a very important point: “It is essential to our argument that many, if not most, Primates can walk bipedally if need be, but also essential to remember that no nonhuman Primate regularly and habitually uses bipedal locomotion.” Hewes (1961:688.)

The paper’s argument is, perhaps, best summarised by this paragraph:


Stated simply, our problem is this: why did certain quadrupedal Primates already capable like other Primates of sporadic bipedalism, become habitual bipeds? … Our suggested answer, to be elaborated below, is: because the effective use of a new food resource required its transport over considerable distances, and only by bipedal locomotion, by freeing the arms and hands for carrying, could achieve maximal transport efficiency. Obviously we are dealing with a time before the invention of pack-straps and side-saddles – cultural solutions to animal transport which permit even hoofed quadrupeds to carry loads for long distances.

Hewes (1961:689)


Hewes reviews the early (pre 1960) literature about bipedal origin hypotheses but generally favours a model which specifically postulates carrying bulk food items (rather than infants, tools or weapons) ‘long distances’ as the only factor which could have driven this change in locomotion.

There is no doubt about which kind of food he is referring to, meat, (p697) but then offers some debate about how this meat might have been procured. Hewes appears to be quite set against the notion that early bipeds were hunters and argues against weapon carrying models, thus favouring a distinct scavenging model (p698).

Later in the paper when postulating a habitat where this could have feasibly occurred, he suggests the gallery forest. He writes “Changes in habitat are amongst the prime movers of biological evolution. Contemporary paleoanthropological opinion places the transition to hominid status in tropical park-savannah lands, where narrow forest environments extend along river courses, flanked by grassy plains (Washburn and Howell 1960:37)” Hewes (1961:700.)

In a second paper, in 1964, Hewes carried the idea a little further and backed it up with some new empirical evidence from four independent reports of wild and semi-feral bipedal food carrying apes and monkeys from the Congo, Tanganyika, Japan and a Puerto Rican monkey colony. On the basis of these findings, Hewes backed away, slightly, from the notion that it was meat-eating that was necessarily the object of carriage and, interestingly in the context of this work, appeared quite compelled by the idea that moving through water might have also been a factor.

Hewes wrote:


“Hardy's hypothesis of an "aquatic past" for man was doubtless extreme, but some of his notions seem less improbable in the light of Kawai’s remarkable report [of Japanese macaques adopting bipedalism partly for carrying objects and partly for moving in the shallows]. In many parts of southeast Asia, macaques have taken up a beachcombing existence: I am not aware of any reports of bipedal locomotion to an unusual degree amongst these littoral primates, but perhaps previous observers did not pay sufficient attention to the matter.” Hewes (1964:418)


·         Hewes’ assertion that only a bipedal gait could permit them to carry bulky food items with real efficiency is backed up by real evidence in non human primates. By presenting them with a bulky food item and then threatening to take it away again, but “provided that he does not find a safe perch or is not so terrified by his pursuer that he abandons the food burden and reverts to the more rapid quadrupedal gait” (Hewes 1961:693), they will often stay bipedal for extended periods of time. This was further bolstered by four more pieces of observational evidence in 1964.


·         Hewes assumed at the time, “that the burdens transported by the emergent bipedal proto-hominids consisted of animal carcasses or parts thereof” (1961:698) but since the time of the paper a great deal of evidence has emerged suggesting that early bipeds were probably not meat eaters (e.g. Andrews 1981.)  One of Hewes’ major arguments is that bulky, high value food stuffs such as meat would be worth carrying long distances back to safe havens, whereas smaller types of foods would not (Hewes 1961: 697,) although he did move away from this position somewhat in 1964.

·         Hewes’ own argument that scavenging behaviour could have begun on the fringes of gallery forests (to which the early hominids, Hewes argues, were native) where, during droughts, herds of herbivores are likely to water in high concentrations is rather self-defeating as the model actually requires ‘long distance’ carrying of the bulky food items as one of its main pillars. Hewes (1961:701.)

1.1 Survival Value Good 6. Over and above the general notion, Hewes’ model does offer an additionally compelling argument of selection, namely the novel niche of following migratory ungulates.    
1.2 Sexual Selection Fair 6: The migration-carrying model provides slightly more scope for sexual selection as it provides greater scope for 'division of labour' between ths sexes.    
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 Good: 9: This was rated highly because the whole model is based on improved food acquisiton.    
2.2 Accounts for Predation Poor 0 : Unlike many carrying models, Hewes idea appears to place putative hominid ancestors at even greater risk than necessary. It is one of his main arguments that women would be able to carry infants alongside the migrating ungulates and this does seem to raise more questions about predation than it solves.    
2.3 Why Apes are not Bipedal Fair 6: This was judged better than the carrying default as it proposes a demarcation between the two lineages.    
2.4 Extant Analogues Poor 2: Conversely, great apes have not been associated with migrating herds and so the model was judged poorly by this criterion.    
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 5: 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 7: Because of the inclusion of gallery forests into the model, this evaluation was better than the carrying average.
3.3 Precursor to Strider and knuckle Walker Fair 5: The long distance aspect of this model gave it a slight edge compared to the carrying average.    
4.1 Extended Explanatory Power Poor 4: Hewes model does not attempt to explain any other aspects of the process of homininization than our bipedality.    
4.2 Complimentary Fair 6: Although Hewes argues against weapon holding and hunting his model appears to be compatible with them. The general notion of following migrating herds out on the open savannah has been contradicted by several other models recently.    
4.3 Falsifiable or Testable Fair 5 : Hewes (1961) paper did make “an effort to set forth a reasonable and sufficient explanation [as to why bipedalism may have originated] which has the further merit of being experimentally testable, within limits, using infrahuman Primate subjects.” Hewes (1961:688) and at the end of the paper early experimental procedures were outlined which the Anthropology Department of Colorado had undertaken with stump-tail monkeys (macaques?). Their plan was to attempt to elicit behavioural scenarios which would elicit incidents of bipedalism in their primate subjects, especially those including food carriage.    
References Hewes GW. (1961) Food Transport and the Origin of Hominid Bipedalism. Am. Anthropol. ;  63: 687-710.
Hewes, GW. (1964). Hominid Bipedalism: Independent Evidence for the Food-Carrying Theory. Science Vol:146 Pages:416-418.