Graham Richards

North East London Polytechnic, Psychology Department, The Green, Romford Road, London El5 4LZ

Received 5 December 1985 Revision received 17 March 1986 and accepted 17 March 1986

Keywords: bipedatism, hominid evolution, manual behaviour, neurological organization.

Freed Hands or Enslaved Feet? A Note on the Behavioural Implications of Ground- dwell ing Bipedalism

It is argued that the routine portrayal of ground-dwelling bipedalism as involving an immediate and dramatic "freeing of the hands" obscures the more plausible scenario of a continuation into the new environment of the previous behavioural repertoire, including branch holding. Both the degrees of prior "enslavement" and of subsequent liberation are customarily exaggerated. It is suggested that the precise behavioural meanings of the terms "tool-usage" and "tool-making" are far from clear. It is not the complexity of particular behavioural schema which changes initially following the shift to ground-dwelling, but the variety of their outcomes as they are applied to novel ol~iects. Feedback loops linking hand-usage and encephalization did not immediately ensue either, although neurological re-organization probably did, but this is more reasonably ascribed to the '~ of the foot than to the "freeing" of the hand as such.

Journal of Human Evolution (1986) 15, 143-150

I t is now a virtual clicha in expositions of human evolution to refer to the "freeing of the hand" which accompanied the transition from an arboreal life style to a ground-dwelling, bipedal, one; "their hands became free to make and manipulate tools" (Oakley, 1975) is typical. Curiously enough, accompanying illustrations by such artists as Zdenek Burian (Pfeiffer, 1970; Mazak, 1980), Matternes (Isaac & McCown, 1976) and Wilson (Roberts, 1980) frequently depict early hominids from Australopithecus onwards as holding sticks. A case perhaps of the right hemisphere not letting the left one know what it is doing, for these sticks receive scant at tention in the texts, al though presumably they are author-approved. The artistic intuition is in any case probably correct, since it is unlikely that an ex-tree dweller would abandon the branch-clutching habit on becoming terrestrial, only to re-acquire it later on having invented the spear. (Nevertheless in the light of Marzke 's , 1983, analysis of the A. afarensis hand, the illustration in Mazak of this hominid using a squeeze-grip rather than a hook-grip is incorrect.) The argument proposed here is that there was no sudden "freeing" of the hand at all, but a transfer into the new life-style of many of the same motor-co-ordinat ion habits which had characterized the preceding arboreal phase. To put it in Piagetian terms, the novelty lay not so much in the adoption of new behavioural schema, but in the outcomes which resulted when assimilating to the existing schema the objects of the terrestrial environment. It was the objects towards which it was directed, not the behaviour itself which changed. As far as changes in neurological organizat ion are concerned, it will be argued that the complementary "enslavement of the foot" was actually more significant.

The phrase "freed hand" is a misleadingly dramatic formulation. The terrain on which the earliest hominids lived might well have been sufficiently rugged to require continued use of cl imbing skills, aside from tree-climbing to escape predators. The old image of a descent from trees to fiat savannah is fast disappearing from the literature in favour of an ecologically complex transition environment of volcanoes, lakes, gallery forests etc. in N.E. Africa (e.g. in Lovejoy's 1981 paper).

I t is also unclear how great the supposedly enslaving locomotor commitment of hands was

0047-2484/86/030143 + 08 $03.00/0 �9 1986 Academic Press Inc. (London) Limited

144 G. RICHARDS

in arboreal life. (Brachiation for instance may not have been a significant feature of the adult arboreal protohominid's behavioural repertoire if they resembled current great apes (Marzke, p.c.).) In fact the term "quadrumanous" rather than "quadrupedal" was traditionally felt apter for the living great apes (more especially chimpanzees)--so much so that Cuvier misleadingly adopted it to differentiate them from '"bimanous" Homo at the family level. This suggests that the enslavement of the foot represented a somewhat greater change of use than the continuing manipulatory behaviour of the hands.

Our first question then is; how far were the behavioural schema required for protohominid arboreal locomotion actually different from, or incompatible with, those required for manipulation tasks? A further enquiry might be how great the actual change was in the ratio of locomotor to manipulation behaviour involved in the shift to the ground, and how rapidly this shift was achieved. (Is it not even within the bounds of possibility that the first ground-dwellers needed tree-limbs as supplementary supports in sustaining prolonged upright posture--after all plenty of people still do?) The answer to the first question must (granted low-brachiation levels) surely be "not much", since the gripping, grasping and pulling operations involved in locomotion are also central to object manipulation. Nevertheless the need to maintain climbing adaptations may have been a factor in the great apes' adoption of knuckle-~walking as their terrestrial locomotive style (Langdon, 1985). Since there is no evidence of a knuckle-walking phase in hominids this might suggest that they were more rapidly committed to a primarily ground-dwelling life-style. One change, implicit in the arguments which focus on carrying behaviour, is that ground-dwelling bipedalism does enable one to hold things longer (and retrieve them if dropped), i.e. there was an extension of the time available for single-object manipulation and sensory exploration in all modes.

Vauclair & Bard's (1983) comparative study of object manipulation in human, Pan troglodytes and P. paniscus infants revealed a t~r higher degree of "richness" in the human subject's behaviour. The key qualitative difference between this subject and the other two was the presence of"tert iary circular reactions", that is to say manipulation of objects with respect to one another rather than simply in relation to their own body or a non-manipulated object (primary and secondary respectively). The basic manipulatory operations themselves were however common to all subjects, though with varying frequency patterns. Vauclair (1982) has briefly summarized the evidence that the complex forms of object manipulation are facilitated by an intensity of communicative social interaction during early development which is unique to humans, though a relatively extended period of postnatal brain maturation would seem to be a necessary condition for this. Although early hominization is now widely viewed as involving shifts in social organization permitting, among other things, longer maturation periods, it is unlikely that the maturity of the neonate brain could have been reduced very rapidly, and logically the change in social behaviour would seem to be primary. Ground-dwelling may well have also been necessary for the acquisition of these "tertiary circular reactions" as providing the physically stable setting on which such behaviour depends, but this too would be a long-term rather than immediate consequence of terrestrial living.

Using the Piagetian concepts of "accommodation" and "assimilation" (Wynn, 1979, 1981) the emergence of tool-use can be plausibly pictured as resulting from relatively minor accommodations of existing behavioural schema following the move from the trees. The evidence of tool-use in chimpanzees is now abundant and it is reasonable to assume that

FREED HANDS OR ENSLAVED FEET? 145

the changes in tool-use accompanying ground-dwelling were at first quantitative rather than qualitative. This is perhaps reinforced by the probability that the transition to the ground was itself initially a quantitative rather than qualitative matter. Our last common ancestor with the great apes may already have been terrestrial to some extent (Langdon, 1985), while, conversely, Lewis (1981) argues that arboreal adaptations of the foot were present as late as Homo habilis. (Leaving aside the vexed question ofA. afarensis arboreality.) The notion of"tool-use" is in any case far from clearcut, and a behavioural operation which on one occasion appears to be non-tool using might look otherwise on another, e.g. hitting a branch with a nut (to crack the latter) compared with hitting a bone with a rock (to crack the former).

In both cases a "hit x wi thy" schema is used, but we more readily ascribe tool status to the rock than the branch.

The further step of "using tools to make tools" is generally given dramatic significance (e.g. Leakey, 1979) as a uniquely hominid advance of radically novel logical complexity carrying deep psychological implications such as the possession of "foresight". This of course moves us beyond the immediate shift to ground-dwelling but it is worth observing that no mighty leap is really entailed in shifting from using a rock to crack a nut to using a rock to crack another rock. In rock-breaking one of the rocks involved is bound to be a "tool to make a tool"- - the one which does not break. The cracked nut may differ from the worked rock in being for immediate rather than delayed use, but even so great ape parallels exist (e.g. the famous termite "fishing" sticks of chimpanzees, which are apparently curated). Is it "tool-to-make-tools" plus "deferred use" which is unique then? Perhaps, but the present point is that such boundaries are (a) often far ti~om clearcut and (b) very difficult to operationalize. The growing literature on primate behaviour in this area is full of examples which nudge the borderlines once held to be so self-evident.

One difficulty with this whole area is that inferring processes such as "planning" from the apparent logical complexity of overt behaviour is so unreliable. Psychology long ago found this out and it would be a pity ifpalaeoanthropology found itself replaying the sort of controversies which racked psychology in the twenties and thirties. The issue then was the ability ofsimpte learning mechanisms such as classical Stimulus-Response conditioning to account for complex behaviour and phenomena such as "insight learning". We now know that no objectively definable "Rubicon" between the two is identifiable, but rather a steady increment in the degree of cognitive processing between S and R, and a hierarchical nesting of longer-term "plans" within which behaviour is integrated. There is no obvious point at which planning and foresight enter the picture, no way of unambiguously operationalizing their presence. The proposition that even tool-making to a regular pattern and for deferred use implies "a marked capacity for conceptual thought" (Oakley, 1975) is not self-evident, indeed no psychologist would be so reckless as to venture it unqualified. After all the nest-building of birds is often both to a regular pattern and for deferred use, while Beck (1982) demonstrates the "foresight" of herring gulls quite convincingly. In some situations we take regularity of patterning as evidence for quite the opposite conclusion--that the behaviour is under rigid built-in pre-programmed control (e.g. honeycombs).

The level of overall integration and com]~exity required of a string of behavioural operations for us to have to invoke the uniquely high level of cognitive skills which we assume characterizes Homo sapiens is at present impossible to say, let alone whether strings of such a kind are implied by the current palaeontological and archaeological data on early

146 ~. RICHARDS

hominids. The stringing together of behavioural operations does not of itself require that the operations themselves be novel. It is in any case now contentious whether Homo habilis made tools to a regular pattern (Wynn, 1981), even after at least 1 ! 2 million years of hominid bipedal ground-walking. "Freeing of the hand" can thus hardly be claimed to have led in any immediate sense to stone tool making.

The transfer from arboreal life to ground dwelling has the initial effect of reversing (though not complexifying) the structure of many common manipulative actions. Operations which hitherto moved the animal now move the object; a backward swing becomes a forward thrust, instead of the animal swinging, the branch is waved, and so on. Thus basic schema of waving, poking, throwing and hitting were already present in the tree-dwelling protohominid's behavioural repertoire--or could be added to it with minimal accommodation of existing schema such as variations in placement of grip-release operations. On becoming terrestrial the hand was never then "freed" from branch-holding, it brought the branch with it, as innumerable artist's impressions testify, along with the appropriate co-ordination schema, only now the outcomes of these changed and novel reinforcement patterns emerged for engaging in them. It could be argued that even now many of us find a freed hand uncomfortable, feeling far more at ease holding something, be it a cigarette, a glass, a pen, a walking stick, the lapel of a jacket, something in our pocket, worry-beads, a necklace, or a stray lock of hair. Indeed we seem to be happiest with one hand, at least, engaged in gripping behaviour, even after more than four million years (at the very minimum).

Similar comments might be made regarding fruit and nut foraging, in which a whole range of co-ordinated plucking, picking, pulling, twisting and tugging behaviours are required, most present in Pan or Pongo. Transferred to the new situation these plucking and picking habits will continue, but will encounter a new range of objects not found in the trees, notably bones and stones. The substance of maximal hardness in the arboreal habitat would usually have been the wood of the tree in which one happened to be located at the time, rocks in particular now present a new grade of hardness and sharpness. It is possible, for the first time perhaps, that one hand will be manipulating an object significantly harder and sharper than the branch held in the other. This extension of the hardness and sharpness range was no doubt a crucial discovery, but its exploitation required little in the way of immediate major behavioural innovation; the schema already evolved for branch-manipulation, nut-cracking and fruit-foraging are quite serviceable with relatively little change other than accomodative fine-tuning. I f Parker & Gibson (1979) are at all right about the crucial role of extractive foraging, the requisite motor operations for this would already be in the protohominid repertoire prior to exposure to those environmental factors which rendered it so important. One should perhaps remark in passing that as far as stone-working is concerned bipedalism as such is largely irrelevant, it was the provision of stable working surfaces, and actual access to rocks, which made ground-dwelling crucial.

Since writers on human evolution are bound to speculate anyway, it is advisable that they do so as plausibly as possible. There are no reasons for supposing that behavioural evolution occurred in a less (or more) smooth way than did physical evolution. The now ritualized references to "freeing the hand" following bipedal ground-dwelling neglect the more plausible picture of a continuation in this new environment of virtually the same manual behaviour and habits as previously. It was surely the objects and consequences of the behaviour which changed initially, not the behaviour itself; the detached stick replacing

FREED HANDS OR ENSLAVED FEET? 147

the attached branch, rocks and stones supplementing fi~uit and nuts as objects to be picked up, knocked, thrown and broken, skinning of carcasses supplementing stripping of bark. Even so, identifiably utilized stone tools do not appear for over a million years after the Laetoli footprints, being apparently absent fi'om all known pre-Olduvai sites such as East Turkana and Hadar (a point reiterated by Mary Leakey as recently as November 1985). Absence of evidence is, proverbially, not evidence of absence, but in this case absence from the record of such robust material as worked rock alongside survival of such delicate phenomena as footprints and fossils must be interpreted, however provisionally, as reflecting the true situation, or at least we must proceed on that assumption.

Existing behavioural schema were thus pre-adapted to the needs of the ground-dwelling biped, provided only that it was capable of recognizing a reward when it received one. Such a picture is consistent With the relatively small brain-size ofaustralopithecines and the long period of virtual stasis for this feature (Godfrey & Jacobs, 1981). It suggests that the feedback loops linking increased encephalization and manual dexterity were not established until later in the human story, perhaps with the advent of Homo itself, under as yet obscure circumstances.

More likely is the occurrence of internal neurological re-organization as Holloway has long been arguing (see Hoiloway, 1983, for a recent statement), claiming at least suggestive evidence for this (Holloway & LaCoste-Lareymondie, 1982). In this connection we need to consider the consequences of the enslavement of the foot in releasing neurological resources. The description of the foot as "enslaved" refers here to its loss of "manual" functions and the subsequent subordination of its morphology to the twin functions of ensuring stability of stance and facilitating bipedal walking. Devine (1985) has recently drawn attention to the diversity of" modern human gait and locomotion in general, but these are better conceived as matters of total postnrat ilexibility, in which dexterity of the foot per se is not the central factor.

The evolution of "quadrumanous" behaviour would presumably have required the development of cerebral neurological equipment capable of integrating the inputs from, and co-ordinating the behaviour of, four "hands". What happens to this when bipedality emerges? Although clearly bipedality will involve further neurological adjustment, the restriction of the lower limbs to a primarily locomotive function, in particular the gross reduction in foot-use for "manual" behaviour, would effectively release a considerable chunk of the quadrumanous processing capacity for alternative use--and where else than in elaboration of the behaviours of the remaining two hands with which it is already closely interrelated? (In this context the finding (Holloway & LaCoste-Lareymondie, 1982) that A. afarensis brains show signs of morphological deviance from the great ape pattern, notably a possible expansion of the relative size of the left parietal lobe, is of considerable interest.)

The gorilla foot is also largely limited to locomotor usage without any consequences of this kind, but this could be due to its having become terrestrial prior to the evolution of a sufficiently elaborate quadrumanous arboreal behavioural repertoire--its current level of ability having arisen post-divergence. The fact that some current estimates, based on molecular evidence (Andrews, 1985) place the gorilla divergence from the common ancestor perhaps two million years earlier than the Pan~Homo one suggests that this may be plausible. Nor is the gorilla's dense jungle habitat comparable to that of early hominids, offering little opportunity for striding gait, or running. The post-divergence evolutionary histories of the great apes are at present too obscure to shed any light on comparative

148 6. RICHARDS

hominid/pongid hand morphologies in the Plio-Pleistocene. This concentration of the neurological resources hitherto required to integrate four

"hands" on only two would seem to be a factor to be taken into account in attempts at reconstructing the manner in which protohominid behaviour evolved. How far does the cortical region now responsible for manual co-ordination and control represent an assimilation of that earlier involved in foot co-ordination? Direct evidence is unavailable but comparison of Homo and Pan cortical mapping shows the human foot representation to be "small and buried medially within the brain; the foot representations of monkeys and apes are larger and extend onto the lateral surfaces of their brains" (Falk, p.c.) implying rearrangement at least, if not takeover, while recent work by Merzenich (Fox, 1984) strongly suggests that the representation areas possess the requisite degree of dynamic plasticity for changes of this kind to bccur fairly rapidly.

A further, tentative, speculation is that loss of two out of four hands would presumably have presented a number of difficulties for a hitherto "quadramanous" species. One partial rectification would be to increase usage of the mouth for some grasping and gripping functions previously perlbrmable by a now lost hand. It is fairly commonplace to construe the tools used in food-processing as surrogate teeth, the hand by implication becoming a surrogate jaw. That the jaws may become surrogate hands is less often noted but, again, could have important ramifications as far as cerebral neurological integration of manipulatory behaviour is concerned.

The net neurological effect of enslavement of the foot then would be to bring about reorganization, rather than enlargement, at the cerebral level; the expansion of manual control areas into those hitherto used for foot control, a need, now two instead of four hands are available, to monitor their functions, and differentiate between them, more effectively, perhaps contributing to lateralization, and so on. The "freed hand" did not immediately generate any obviously discernible gross neurological change of a radical nature. Dean Falk (1980, 1983) has consistently adopted a more sceptical line on the presence of morphological evidence for cerebreal re-organization in australopithecines. Re-allocation of foot-representation areas of the cortex to the hands would in itself be unlikely to leave any trace in the fossil endocast record. If Falk is right the present thesis is if anything strengthened further, the existing brain structure continuing to serve the newly bipedal ancestor quite adequately. Such changes as might be expected to have found morphological expression, notably incipient lateralization of function, are, though, those which Holloway & LaCoste-Lareymondie tentatively discerned. Vilensky et al. (1982) in any case suggest that limbic system changes were at least as fundamental as cortical ones in the early phases ofhominization, and these are less likely than cortical changes to leave any palaeontological trace (the changes they are concerned with do not however directly relate to the current issue).

Marzke's anatomical review of the capacities of the A. afarensis hand would seem to support the present perspective. Although having a smaller behavioural repertoire than modern humans, the combination of hook-grip, pad-to-side and three-jaw chuck postures is alone sufficient to facilitate hammering, digging, cutting and throwing (though not necessarily very accurately). Lucy's deficiency lay in the power grips rather than in the precision grips, being superior to Pan in most respects pertaining to tool use. Perhaps the subsequent selective vector was for optimizing brawn rather than brain, the energetically expensive evolution of a larger brain becoming advantageous only when all the possibilities

FREED HANDS OR ENSLAVED FEET? 149

of adding power to the already complex repertoire of manual operations had been exhausted, and higher order "chunking" and stringing came into its own.

My approach is broadly in line with those of Parker & Gibson and Wynn, to whose papers the reader is referred for fuller accounts of Piagetian concepts and their use in modelling h u m a n behavioural evolution. Although it does not depend on a strict acceptance of the full Piagetian theory, his terminology is part icularly convenient. The basic assumption is that both ontogenetica!ly and phylogenetically behavioural schemata or "operat ions" emerge from schemata of a more logically restricted or simpler type and do so in a fairly smooth fashion. This smoothness is periodically interrupted by more dramat ic episodes of structural reorganization of the system as a whole, marked by the appearance of schemata of a fundamental ly different logical order, thereby simplifying and stabilizing it. I have been arguing that such a re-organization did not necessarily follow the abandonmen t of the arboreal habi tat as is customarily assumed. The new ground-dwell ing arena may even be interpreted as having given existing schemata a new lease of life. The extent to which this approach involves "recapitulat ion" in the usual sense is currently in dispute (Parker & Gibson, 1982), but discussion of this is beyond the scope of the present paper other than to point out that if we are dealing with a developmental sequence which is logically necessary then the general strictures against recapitulationism might not apply. The points made here in any case appear to be valid regardless of the recapitulation issue.

In conclusion then, I am arguing that the continued habitual use of phrases like "freed hand" and facile jumping to psychological conclusions about "planning" and "foresight" on the basis of ambiguous artefact evidence are likely to prove at worst misleading and at best a distraction from some impor tant aspects of the psychological dimension of early hominid evolution. Psychological speculation is inevitable; let's get it right. Talking about "freed hands" when there is little indication as to whether they were either enslaved in the first place or in any genuine sense "liberated" subsequently, helps nobody unders tand what really happened. Perhaps a "figure-ground" switch of attention to the implications of the less disputable enslavement of the foot might prove a fruitful tactic at this stage. As Wood Jones once wrily wrote;

Man's foot is all his own. It is unlike any other foo t . . , he must not ever forget that it is, in fact, his feet that confer upon him his only real distinction and provide his only valid claim to human status (1944, p. 2).

Acknowledgements

I would like to acknowledge the helpful comments by Dean Falk and Mary Marzke on an earlier draft of this paper.

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