by Paul Jordan
Aegyptopithecus.
Proconsul.
The differences between chimps and men, both in appearance and behaviour, are great. Human beings, unlike all other primates, can walk bipedally, on two legs, with pelvis and spine adapted in shape to this form of locomotion, whereas chimpanzees can at best walk for only short distances in an awkward fashion on their legs alone and usually go about on all fours, knuckle-walking with their long arms. Humans have tiny canine teeth in comparison to those of the chimps, and flat faces with protruding noses in place of the prognathous muzzles of our nearest animal relatives. Human teeth are arranged in a curved arcade instead of the parallel-sided and rather box-like arrangement of ape jaws. Humans are relatively hairless except for their heads, armpits, and pubic areas, and they sweat all over. Human males’ penises are large and pendulous by comparison with chimps’ while, uniquely among primates, signs of ovulation are suppressed in human females. Human beings eat (and share) meat on a much more regular basis than chimpanzees do and, among foraging peoples, hunt cooperatively to acquire it (which chimps do not do on anything like the same scale). Even the most ‘Stone Age’ of human groups make tools in large numbers to a regular and culturally coloured pattern and communicate with complex languages which chimps lack altogether, as they do every sort of symbolic expression. Humans are culturally adapted to survive in almost every environment this world affords, however hot or cold, dry or wet; they will eat just about anything that can safely be eaten, with cooking to render edible even certain foodstuffs that could not otherwise be eaten. Victorian explorers occasionally reported seeing apes warming themselves in the heat of dying embers of natural fires, but chimpanzees cannot make fire or control it when it occurs in nature. Human beings have much bigger brains in relation to their body size than chimps do and are manifestly cleverer in every way, with powerful hands capable of a fine dexterity to carry out the clever purposes of their brains. Human beings, moreover, are markedly ‘handed’, right or sometimes left, which is a situation not seen in any other creatures. They are long-lived and their children mature postnatally much more slowly than ape infants, with an extended period of learning that includes an adolescent boost to growth and sexual maturity.
The way of life of the chimpanzees does show some faint resemblance to that of foraging Homo sapiens sapiens. They do eat meat on occasion (young monkeys, for example) and acquire it sometimes by means of cooperative hunting operations, involving driving prey towards their fellows or blocking escape routes. This is a clear advance on any monkey performance; though baboons (whose life in troops brings them, too, some resemblance to the human hunter-gatherers’ situation) will now and then catch hares or small antelopes, they do not organize themselves cooperatively to do it and they do not share their pickings. Chimpanzees will hunt socially from time to time but they are essentially opportunistic, without perseverance and often ignoring easily caught prey under their noses. They are not, unlike modern and Upper Palaeolithic hunters, good stalkers or chasers. Plant food is the main component of their diet and they get it individually and eat it on the spot. They use no weapons in the hunt and no tools to cut up their meat (biting, bashing and twisting off heads is their style). In play chimpanzee youngsters will occasionally throw sticks and stones, but adults in real fights resort to no weapons but their own teeth. Chimpanzees do use and even make tools sometimes, but in the wilds this is only a matter of stripping leaves off a twig to make a stick to poke into a termite nest or crumpling up a handful of leaves to use as a sponge; stones are sometimes used to help break up food. This level of toolmaking and use is really only an extension of the cleverness of food acquisition seen in the big-brained and stereoscopically sighted primates from way back. Tools at the chimp level are made without any specialized techniques: pulling leaves off a twig is just like pulling off leaves to eat. Young chimps, moreover, are slow to learn from their elders in tool-using groups. Even after tediously repeated demonstrations, experimenters have been unable to teach chimpanzees to use an Acheulian hand-axe to make their twig tools. The concept of using a tool to make a tool, with all its connotations of foresight and prefiguring in the mind’s eye, is evidently beyond the chimpanzees. They cannot be induced to make even the simplest sort of Oldowan pebble tool, though they have been interested in smashing off flakes that resemble the very earliest pre-Oldowan ‘tools’ that have ever been identified in the archaeological record. (Gorillas, incidentally, do not use tools at all, nor do the pygmy chimpanzees.)
Attempts have been made to teach chimpanzees the use of language by signing according to systems employed by the deaf and dumb, and more recently with special computer keyboards. They are not physically capable of the vocal production of language, any more presumably than our common ancestor with them of six or so million years ago can have been. But they can learn to interpret and use for themselves some of the signs taught to them by their human teachers. These are mostly, if not exclusively, signs for concrete things or actions and everyone recognizes their quite impressive feats with these signs. Contention arises where some workers have claimed a degree of concept-building on the part of chimps using signs; a famous example involved the signing for ‘water’ plus ‘bird’ when a particular chimpanzee encountered a duck, but most researchers have concluded that even this extent of conceptualization is not proven by the evidence and that syntax, the complex arrangement of words into abstract relationships in the mind, is beyond the chimpanzees. Their use of language is really restricted to demands with very little in the way of comment on the world about them, vastly inferior to the language skills of a human three-year-old. And no ape infant has ever learned signing from a parent capable of it. In the wild chimpanzees merely produce sounds (growls, screams, barks) to communicate a very limited range of moods and wants and warnings, in association with grimaces and posturings. It is even suggested that a different part of the brain is employed to control these sounds from the parts employed by humans to generate vocalization.
Chimpanzee society is based on the females’ relationship with their infants. Females tend to forage for themselves and their young offspring, taking plant food and insects. Males roam between the females of their group, looking for sexual opportunities as they arise and warding off rivals as far as they can. On the whole they undertake the hunting of animal prey, though females do sometimes join in that activity, which certainly shows a degree of cooperation at times, with some meat sharing as a result. Chimps do not scavenge dead animals or take over the kills of other predators.
It is in the area of social relations (and strategies) within the group that chimpanzees perhaps reveal their most human-like traits, however unflattering these traits may be at first glance to our time-honoured picture of ourselves at our best. Quite simply, chimpanzees deceive one another and this gift for deception, and being on the look-out for it, represents a colossal advance on the achievements of the lower primates and all the rest of creation, save for mankind where the practice has been brought to new heights. The advance is in the sphere of mental capacity, the imaginative ability to run through behavioural stratagems ‘in the mind’s eye’ and conjecture about their consequences for one’s advantage. Chimpanzees feign intentions that they do not intend to carry through, they pretend not to be about to do things that they mean to do. In these ways they cheat each other out of food and sex – if they can get away with it, for their alertness to possibilities of cheating matches their penchant for doing it. Chimpanzee society is a field of shifting alliances for power, sex and food, facilitated by deception and guile. The chimpanzee mind seems better equipped to deal with this aspect of their lives than any other, though by the standards of most animals they are no mean performers all round. But it is into navigating their way through their social relations that the bigger part of their cleverness is invested. It is as though they make their rudimentary tools and acquire their food in the natural world about them on automatic pilot while their best mental efforts are put into dealing with one ano
ther. To get advantage for oneself in the social context calls for a certain self-consciousness about one’s own desires and possibilities together with an imaginative insight into the potential wants and talents of one’s fellows. Consciousness and imagination (and bigger brains to operate them) look like the products of natural selection in circumstances favouring their development among competing apes in a particular ecological adaptation. Of course, all this begs the question as to what life actually feels like to the chimpanzees, and what quantity and quality of consciousness they experience, but then not one of us has any real idea of what life feels like to our fellow human beings, even those nearest to us. Some researchers believe that consciousness is doomed to remain forever incomprehensible to itself; all we can do (though it is quite a lot, in fact) is to track its adaptive benefits, as it emerged, to our close relatives like the chimps and our evolving ancestors. Chimpanzee ‘consciousness’ (we put it into inverted commas to mark recognition of its inevitable difference from our own) would appear to be largely restricted to the world of social relations, without much application to the natural world or to food acquisition or tool use or sex and reproduction as such. With the chimps, no imagination has been brought to bear on a deeper knowledge of nature, to exploit it more fully, or on tool production to increase hunting and food processing skills – no imaginative powers seem to be available to chimps to focus on these matters even when they are repeatedly nudged by example to develop them. It is as though their mental capacity is severely compartmentalized with many departments flying on autopilot and only their social dealings open to introspection and experimentation. All the same, their minds clearly exceed those of monkeys, even the social baboons, in their complexity and flexibility; chimps (and gorillas) can recognize themselves in a mirror in a way that monkeys cannot and monkeys plainly lack any sense of themselves or of other monkey selves. Chimps do ‘know’ quite a lot about their world and are even able to make tools to work on it (a trait once thought to be the hallmark only of humanity) but they are unable to handle their knowledge creatively; they do not appear to know that they know and they have not tumbled to what can be made of knowledge. Still, they have come far enough along a parallel road with ours to deceive each other to the manner born and even to make war on their own kind in other groups, killing males and taking over females and territory – something in chimpanzee life which shocked human researchers when they first encountered it. And they have done this in an environment rather different from that of our ancestors, whose success can now be seen to have ultimately depended on the extension to all departments of the mind of the sort of mental capacities that are seen in only rudimentary and restricted form among the chimpanzees. It is interesting to learn from psychological tests on human subjects that we ourselves maintain an enhanced mental acuity where problems with a dimension of social cheating and cheat-detection are concerned – conundrums that require alertness to social advantage and disadvantage are solved more frequently and quickly than neutral puzzles. And, of course, cheating and social jockeying have not to be seen as the finest achievements of human mental evolution; it is simply, but very importantly, that increased awareness and inventiveness in these directions appear to have been the motors of all-round mental development. Altruism, impulses like mother love for example, go back a long way in ape and human evolution (chimpanzee mothers have been known to carry around dead infants for days) but such behaviour comes rather easily to creatures evolved to have such impulses, while it requires real agility of mind to fool your fellows. Increased mental agility brings evolutionary advantages to its owners, and in the right circumstances natural selection favours the development of more and more of it, and its ultimate extension beyond the purely social realm into all aspects of survival. When the only moderately clever apes retreated under the impact of aridification after about 10 mya, the cleverer hominids prospered.
Skull of a chimpanzee.
The Lothagam mandible fragment.
Some seven million years ago our ancestors must have resembled a sort of unspecialized chimpanzee, quadrupedal but without the very long arms and knuckle-walking that the chimps and gorillas would go on to evolve, still mainly arboreal but not too evolved in the direction of the living apes to be incapable of adaptation to bipedal locomotion on more open ground: a big-brained, probably black-coated, fruit and insect eating (and maybe already tool-using if not toolmaking) forest dweller that soon diverged into the chimpanzee line and the line of early hominids.
The very earliest hint of what could at least be a genuine hominid comes from Kenya at a date between 6 and 5 mya. The Lothagam mandible is too fragmentary to say for sure that it belonged to an early hominid, but it is at just the time range of this specimen that we can expect to find the first signs of hominid existence (and, indeed, a new find from this age range has recently been reported from the Awash Valley region of Ethiopia). From a time about a million years later comes something more suggestively hominid in the shape of the remains of Ardipithecus ramidus from Ethiopia. The finds, from several individuals (and new ones continue to be made), include teeth and jaw pieces, some arm parts and part of a skull which shows the hole, the foramen magnum, through which the nerves pass to the spinal column on which the skull sits. Unlike the conformation seen in the apes, the hole is well forward under the skull in a manner which suggests the evolution of upright walking: bipedalism. Apes carry their heads thrust forward, with strong musculature to hold them from hanging on their chests, in keeping with their quadrupedal locomotion; human beings have their heads balanced on top of their spines, thanks to their upright bipedalism, with less need of musculature to keep them up. Ardipithecus at about 4.4 mya thus offers a muted indication of the development of bipedal posture and may tentatively be seen as a just incipiently hominid creature living only a short time after the divergence of chimp and human lines. The area where the jaw articulates with the skull is very ape-like in Ardipithecus and the molars and premolars are small but the canine teeth are more hominid in form. Associated floral and faunal remains indicate that Ardipithecus lived in a more wooded environment than was to come in East Africa as the drying associated with the cooling climate of the ice ages progressed.
An ape’s skull needs strong musculature to support it on its inclined spine.
A human skull balances on top of its upright spine.
Australopithecus anamensis from Kenya takes on the hominid line in a period between 4.2 and 3.9 mya. Finds include teeth as well as jaw, tibia and humerus pieces from nine individuals. The jaw arcade is more like those of apes than of men but the leg parts display evidence for bipedalism. The world of A. anamensis was still one of woodland, with some bush, and the teeth indicate a vegetarian form of subsistence. But climatic changes, with the general aridification of the times perhaps exacerbated by mountain building in Kenya and Ethiopia, began to see a growing isolation of the early hominids of East Africa in a drier and less wooded world that was not suited to the lifestyle of their still close relatives the ancestors of the chimps and gorillas, who carried on their lives in the slowly shrinking humid forests further west. In East Africa the grasslands spread at the expense of the wooded areas and we know from the fossil record that faunal evolution produced elephants and rhinos, for example, with teeth better suited to chewing and grazing than before. A. anamensis appears to have given way to A. afarensis after 4 mya, a species whose most famous representative is known to the world as Lucy, dating to about 3.2 mya.
Australopithecus afarensis is known from enough individuals of both sexes, with some fairly complete specimens like Lucy, to make feasible, for the first time in hominid evolution, a rather full account of the physical attributes and lifestyle of the type. There was clear dimorphism between the sexes (and Lucy may yet prove to have been a male). At Hadar in Ethiopia the remains of at least thirteen individuals were found having evidently perished all together, perhaps in a flash flood; there were nine adults and four juveniles, allowing identification of sexual differe
nces. Males were much taller than females, at about 1.5 m vs. l m, and very much heavier at an estimated 65 kg vs. 30 kg. This degree of dimorphism outdoes that seen among the chimps today and resembles the situation of the harem-keeping gorillas, though it may point more to a protective and defensive role in the open grasslands for the males than to a situation of sexual rivalry between the males. Brain size, at between 350 and 500 ml, was in the ape range (but big for body size), in skulls with sloping foreheads and projecting muzzles. But the canine teeth were smaller than those of apes and now the molars were bigger, presumably for chewing harder foods than fruit, like nuts and seeds. Lucy’s short legs and long arms, with rather curving hands, hark back to the generalized ape ancestry of the hominid line, pointing to a way of life not just recently but still in some part arboreal (for example, as far as sleeping arrangements were concerned), but the shorter and broader blades of the pelvis are much more human in their bipedal implications, as are details of femurs, knees and feet, though the walking gait was probably somewhat different from that of subsequent hominids of the genus Homo. The mixed ape-like and human-like traits of afarensis leave no room for doubt that these early hominids were descended from some common ancestor of the apes and men. But it was the hominid branch that was to thrive while the pongid line went into slow retreat.
An Australopithecine dental arcade, not as parabolically open as humans’ are, with large molars but reduced canines.
The Human Line
Australopithecus afarensis enjoyed a long career in East Africa, down to about 3 mya, but left behind no tools that we can identify. It seems very likely that afarensis was at least as handy in the tool-using and toolmaking line as are chimps today; indeed the bipedal posture in freeing the hands from locomotion (except during sojourns in the trees) must have facilitated tool use, so probably the tools in question (such as they were) were made of perishable materials. Be that as it may, it is certain that bipedalism constituted a great step towards the evolution of humanity. Many suggestions have been made to try to explain the coming about of bipedal posture and locomotion. People have pointed out that it reduces the amount of skin area presented to the heating and potentially damaging direct rays of the sun (on the assumption that the presumed thicker pelts of our ape ancestors were shed to promote sweating as an aid to heat loss on the savanna); at the same time, it brings the head up away from the heat-radiating earth and into the cool breezes above ground level. Bipedalism may initially have recommended itself as a means to scamper from one patch of woodland to another as quickly as possible as these familiar places of shelter shrank on the encroaching savanna (and it may have come rather naturally to a creature used to hanging upright from branches). It was an advantage, too, for the Australopithecines to be able to stand up and look over the grasses of their aridifying world for enemies and prey. All these explanations very plausibly relate bipedalism to the ecological changes which saw woodland giving way to grassland during the several millions of years of hominid evolution away from the apes. It was hotter out in the open in the direct light of the sun, with less in the way of shelter and protection not only from the sun’s rays but from enemies in the animal world; and life in the open needed more heat-generating activity at times, to escape enemies and, maybe, run down prey of one’s own as diet turned from the purely vegetarian to elements of meat eating. Standing up and walking freed the hands to carry stones and throw them when danger or opportunity arose. The hands were free, moreover, to evolve into ever better manipulative agents under the pressure of natural selection and thus to work in with ever improving mental performance by bigger brains. Bipedalism may also be seen to have altered the visual appearance that evolving hominids regularly presented to each other, especially perhaps where sexual relations were concerned. The big penises and full breasts of the human line may have evolved in concert with bipedalism, helping ultimately to promote more monogamous relationships between food-sharing males and females with concealed ovulation, with less of the indiscriminate mating of most other primates (including the chimpanzees) who can never track paternity and develop family units. With more in the way of full frontal encounters of every kind, bipedalism must in general have enhanced the subtlety of all social encounters, calling for even more agility of mind to negotiate the social scene and perhaps thereby extending the range of facial and vocal signals that underlie the development of language. At all events bipedalism marks the turning point at which hominids and pongids decisively parted company.
