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)