These pages have been left in this location as a service to the numerous websites around the world which link to this content. The original authors are no longer at the University of Leeds, and the former Centre for Human Biology became the School of Biomedical Sciences which is now part of the Faculty of Biological Sciences.
Lower and Middle Pleistocene - Homo erectus and Homo sapiens
Homo habilis and H rudolfensis didn't last all that long. Pleistocene hominid remains (1.5-0.2mya) are more common, but much less diverse than before. The implications of this are that H habilis and H rudolfensis became extinct as did robust australopithicines. This coincided with a large number of non-primate extinctions, and is thought to be a consequence of a widespread ecological change.
So the picture is of a single type of middle Pleistocene hominid Homo erectus. The material is not completely uniform , of course. Some of this variation represents the passage of time and some geographical spread. Because about 1mya fossil remains begin to appear outside Africa, first in the tropics then in higher latitudes. As the range extended marginal populations were likely to come under increased selection pressures resulting in local adaptation and perhaps temporary isolation and interruption of gene flow.
Pleisocne was an era of climatic change, especially in these newly
colonised high latitudes. Much of Europe and Asia was subjected to long
cold periods, sometimes even glaciation. Apart from the obvious effects
on animals and plants the cold locked up large quantities of Sea water
in ice sheets: sea levels fell linking Britain to Europe and Indonesia
to the Asiatic mainland. Outside the glacial areas rainfall decreased
producing arid conditions in parts of the tropics. The glacial
conditions were not permanent: they were interrupted by interglacial,
usually warmer than at present with higher tropical rainfall.
We also have a good specimen of a virtually complete individual, about 1.6mya and aged about 12 at death. He was tall and ruggedly built, with essentially modern postcranial proportions. The relative lengths of arm and leg are virtually the same as in modern man. Height and weight have been estimated at 1.66m and 55kg. He is considered male on pelvic proportions and pelvic size, and although probably not full grown has a cranial capacity of 900ml.
Although nearly modern postcranially there are one or two interesting features. In modern man the spinous processes of the upper vertebrae slope downwards: in apes and in erectus they are horizontal, suggesting powerful arm muscles. The rib cage is also conical or bell shaped, as in apes, rather than barrel shaped as in humans. The pelvis is narrow, and the femur rather australopithicine in the long neck and low angle of the shaft.
There are other bits and pieces usually placed in H erectus from Olduvai Gorge, South Africa and Kenya.
40 miles West, however and eroded volcanic dome produced more material. Because of the nature of the country and the people most of these finds are incomplete, and recovered by bounties paid to collectors rather than controlled excavation. In spite of this a pattern is emerging, of beds of 0.8-1.0mya containing fossils with a brain of 800-1250 ml The vaults are thick and there is a frontal ridge and often a frontal and/or parietal keel. The occipital bone is extended and angulated as a crest and there is a prominent brow ridge, giving a marked constriction behind the orbits.
There is some variation, then, as we might expect in a series of fossils spanning a couple of hundred thousand years with no clear stratigraphical information. But it looks as if there is just one species in Java, and essentially it is the same erectus as we see a little earlier in Africa. Presumably Asia became accessible and inaccessible as the ice came and went, and there my have been various incursions: but the fossil record is not good enough for us to see deeper at present. Recent finds if verified, will place the Java material considerably earlier.
Mandibular remains are also like Javanese jaws. There is a high degree of incisal shovelling (also characteristic of some modern Asain populations): cheek teeth are reduced to the size of those seen in Aborigines or Eskimos.
Postcranially the Chinese specimens resemble those found in Africa, but are shorter at about five feet.
So where does erectus fit in? The Turkana beds show H.erectus already present at 1.78mya, with most specimens a little later (1.6-1.7mya). Most rudolfensis are 1.85-1.9mya so a little older. H. habilis is contemporary with rudolfensis. It looks as if erectus arose in the burst of hominid diversification in the late Pliocene: neither habilis nor rudolfensis is an appropriate ancestor. Habilis has a similar facial structure chewing apparatus and dentition, but with a lightly constructed vault and a primitive postcranial skeleton. Rudolfensis has an expanded cranial vault, but of a different form and face jaws and dentition are clearly non erectus. Postcranial remains are similar: the worry here is that postcranial rudolfensis remains come from virtually the same beds as erectus and are very nearly contemporary: given the unreliability of the fossil record, are the bits of rudolfensis really erectus? We await confirmation.
So the picture that emerges is one of many hominids in the late Pliocene: habilis is there, rudolfensis is there, erectus is there and so is A. boisei. Presumably all these occupied different niches.
development of H.erectus
However there are also contrasts. Brain size is greater on average, the vault is higher with inflated frontal and more evenly curved occipital regions and the highest part of the vault is around the temporo-parietal suture. The nuchal area is still extensive, but its ridge is less clearly defined. Saggital keeling, although still present, is less than in H. erectus.
Whether a given fossil is erectus or sapiens is thus a grey area. Later middle Pleistocene fossil from all continents show common features, so much so that the same piece of rock has often been assigned to different species by different workers. This is because contentious individuals show combinations of features which were previously thought to be unique to habilis or sapiens. This intermediacy suggests continuity in the fossil record to some workers: others emphasises the contrasts to legitimise the two species. Some workers, as we have already noted, even doubt the case for erectus in Europe, suggesting that claimed erectus are, in fact, early sapiens. However one of the latest European specimens, Bilzingsleben, is particularly erectus like. The chronological records are poor, but more and more intermediates keep turning up, and it does seem that there was a chronological, gradual shift from erectus to sapiens.
Ecology and behaviour
In Africa pebble tool industries continue throughout the period, but tend to display better flaking proficiency and a wider range of forms At Olduvai these developed tools occur from 1.6mya onwards. There are less choppers and more spheroids and small scrapers. Some of these (<5%) are bifaced or two edged.
Only slightly later (1.5mya) we find Acheulian assemblages with sharp and retouched flakes and a greater proportion of bifaced (>40%) shaped into tools of distinct form, almond shaped hand axes or transverse edged cleavers. These tend to be larger, better balanced and more symmetrical than pebble tools, and are more regularly flaked over a greater proportion of the surface. They are often made by retouching large flakes, or struck from large boulders, so that one side is flatter than the other. Materials are carefully chosen for specific tools and transported to a factory: at Gadeb in Ethiopia obsidian used for hand axes has been transported from 100km away.
The likely scenario then is pebble tool early Oldowan becoming developed Oldawan, and this in turn (because of the two edged flakes) becoming Acheulean.
A pattern for H.erectus culture has been developed based on chimpanzee living in similar areas today. The Gadeb sites, for instance are on the highland plateau on either side of the Rift valley . These areas are close to water and would have supported a ribbon of forest in an otherwise open environment. Our best guess is that groups of individuals ranged widely, coming together temporarily to exploit seasonal resources. Gadeb represents a reoccupied base camp in a riverine forest where most food resources exist and from which smaller groups would forage to outlying areas in search of fruits, tubers, insects, meat etc. and for tool materials. Once the resources of a particular base camp area were exhausted the group would move on to another. In this way a considerable range of sites might be occupied, and a large area covered in a year - hence perhaps the obsidian used for hand axes.
With the passage of time we see a possible development of this lifestyle: Acheulian living floors are flatter and larger, tools are better and areas are set aside for different pursuits. By upper Acheulen times there is evidence of postholes for a shelter, fire and ochre at the site.
By the middle Pleistocene we see a wider geographical use of tools. Tool assemblages are found in Morocco, Tunisia, Algeria, and Israel. There are possible sites in France and Italy, but the overwhelming majority of European sites are much later (<0.5mya). The Acheulean style of tool making extends across the Middle East to India, but is not seen in the Far East or South East Asia where Oldowan style pebble tools are found. Does this imply a primitive culture or something else? The reasons for the spread of man out of Africa are obscure, but they would certainly bring him into contact with a different environment. Southern Asian environments are largely tropical, bamboo and monsoon forests, not grassland. Artefacts from N Thailand indicate hominids by late lower Pleistocene (>0.7mya) at about the same time as Chinese and Javan fossils. The sparse findings of stone tools from Asia might suggest that the tool kit was different - bamboo, wood, rattan, bone and that stone tools were used only to make organic tools, which would not survive so well.
Occupation sites are few and far between in Asia: the best known is Zhoukoudian in China, where a cave area was periodically occupied between 0.5 and 0.25mya. Here we find human remains, broken and charred animal bones, ashes, hackberry seeds and quartz flakes and cores. The site has been identified as a winter camp, with use of fire, systematic hunting and the use of plant foods.
H erectus has clear right/left frontal asymmetry and expanded temporal and frontal lobes, which probably means a pretty good brain and complex cognition. H erectus pelvises are narrow and not sexually dimorphic. If we use the general primate formula that neonate brain size is about half the adult value we arrive at 400ml, which would not have fitted through the pelvis. We can therefore argue that the new-born H erectus must have had a smaller brain than this at birth and implies in turn a longer period of childhood i.e. dependence on the mother - a very human pattern.
Further evidence comes from tool patterns. Oldowan tools are crude: Acheulean assemblages show better technique, better balance and proportion. In some sites large numbers of hand axes, for instance, are very regular in size and shape. Experiment shows this pattern to be particularly effective for a number of purposes - dismembering digging, debarking trees. It has been argued that this concept of design means that most of our mental, as well as physical peculiarities developed during the lower and middle Pleistocene. The genus Homo appears.
The OH parietal bones are thin, because of their immaturity, but complete enough to give an estimate of cranial capacity of 645ml. This gives a best guess for the adult of 675ml. The mandible is eroded along the lower border, but clearly strongly built. The canine has a slight wear facet which indicates canine overlap. Cheek teeth are to Australopithicine sizes but the premolars are narrow. Third molars had not erupted, giving an age equivalent to a human 12 year old. So the differences between Australopithecus and H habilis are
The hands are powerful with slightly curved phalanges. The joint at the base of the thumb is saddle shaped like ours. The foot bones are rather small, but definitely bipedal, with well developed arches and an adducted big toe. The clavicle is stout, but otherwise like that of a modern man.
Three years later another one turned up. OH13 or Cinderella was a little older, with third molars just coming into occlusion and a cranial capacity of 673ml.
The Leakeys also recovered bits of George. George (OH16) had been badly trampled by Masai cattle and was in over a hundred bits, but was evidently an adult male with large teeth, a well developed brow ridge and a vault of cranial capacity 638ml.
In 1969 Mary Leakey found a remarkably complete cranium (OH24 Twiggy) . This was crushed and distorted but small and lightly built with a cranial capacity of 600ml. OH62 discovered in 1986 had some limb bones: at least some individuals were short and had powerful proportions which resembled Lucy, 1m year older.
On the basis of OH7, Cinderella and bits of George Homo habilis was established in 1964: Twiggy and OH62 were assigned to this species when found.
KNMER 1813 (CAST) is a lightly built individual with a thin walled vault and a cranial capacity of around 500ml. The brow ridge (supraorbital torus) is moderately developed and the mid face has limited prognathism. The cheeks are lightly built and the dental arcade parabolic with small teeth.
KNMER 1470 (CAST, SLIDE) in contrast has a cranial capacity of 775ml, less in the way of a supraorbital torus and a very flat face. Precise relationships between parts are a little dodgy because of distortion of the fossil.
Other less complete crania are more or less intermediate between these two. There are also many fossil mandibles separated from crania. Some of these are obviously A boisei but others are more lightly built. Wood divided these lightly built mandibles into two distinct groups.
Postcranial remains include at least four partial skeletons and many fragmentary long bones, especially femora. These have not been fully analysed, but two part skeletons are believed to be Homo habilis. One of these ER3735 includes some skull parts, which look like ER1813 and parts of an arm and leg. The forearm is similar in size to a chimp, with powerful shoulder muscle markings and strong flexion at elbow and digits that suggest climbing ability. This is much larger than Lucy's forelimb, but hind limbs are nearly equal.
So what do we make of Homo habilis? In the announcement of habilis Leakey was doing something rather more profound than just setting up a new species: he was redefining Homo as well. Leakey argued that Homo should be defined not narrowly on one or two particular features but broadly on overall features. Man, he said, has truncal erectness, bipedal locomotion and precise manipulation even if these occur with a cranial capacity of 600ml (previous thought was that about 750ml was need to qualify as a human brain. Individual early Homo brains may thus overlap with Australopithecus but the average human brain would be larger than the average Australopithecine, absolutely and in relation to body size. Muscle markings could be weak or strongly developed, the face flat or projecting but not dished. Teeth should be set in an even curve and the molars smaller than in Australopithecus and incisors and canines should be large relative to cheek teeth. The teeth in Homo are also generally narrower.
Both the revised genus and the new species were criticised at the time, but more recent finds have confirmed these ideas. The brain of H habilis is now seen to be more human than Australopithicine in proportions and the latest estimates of 640ml put it 25-40% bigger. Later finds also confirm the smaller molars with thinner enamel: the jaw musculature and tooth wear is reduced, and the smaller jaws and teeth suggest a head balanced on the spine in a more human fashion.
Diversity in early Homo
As on all borders there are disputes. In the main Leakey's arguments have prevailed, and these fossils are seen as Homo, with occasional skirmishes about individual fossils: this is bound to happen in a mixed deposit of variable individuals.
Putting all known 'habilis' fossils into one group is certainly the simplest alternative. But if we do this we run the risk of not recognising significant differences in the material. There is also a risk of habilis becoming a dumping ground for all sorts of bits and pieces of rock that don't quite fit elsewhere. And there is the gut feeling, or the opinion based on other living and fossil primates that there is simply too much variation in this group of fossils to represent one species.
The other view, that there are two species, seems to be a more reasonable approach: more than two species adds even more complication.
If we believe in one species of habilis how do we see the phylogeny? Tobias, the main proponent of this view suggests that A africanus is a common ancestor of both a robust Australopithicine and H habilis. The robust clade had bigger teeth and jaws, the habilis went the other way, with smaller jaws and more brain power. If we start from two groups of habilis instead of one then Stringer found the 1470 group more primitive than the 1813 while Wood's latest analysis finds them to be sister groups.
summarise the main points of this argument
Another interesting factor enters the fossil record at this point: we begin to find artefacts, tools at both Olduvai and Lake Turkana . These tools are generally regarded as made and used by Homo although they could be Australopithecus: but at no site are tools and Australopithecus found together without Homo.
The earliest tools we know of are from the Omo valley in Ethiopia. These are sharp quartz flakes struck from quartz pebbles. Signs of use (i.e. wear) are rare. Olduvai and Turkana tools are a little more advanced. These tools are flakes of quartz and small cobbles from which flakes have been struck. Retouching and signs of wear are still rare and the earliest tools are from a thin strata, implying transient occupation; sometimes there are repeats suggesting periodic occupation of a site. all occur on river edges, close to cover.
These are usually referred to as Oldawan or pebble tool assemblages. The cores may be pounders or choppers, but it seems more likely that they are simply cores used to produce flakes. Flakes are very effective in cutting hide and disarticulating joints. The tool sites may represent caches in the landscape deposited perhaps for future use. This implies selectivity and foresight. This use of tools is often associated with a fancied increase in meat eating, though whether cause or effect is open to doubt. Oldawan tools show no evidence of style or design. They were probably a response to one off need. However the ability to make them implies a knowledge of stone structure and behaviour which exceeds that of all modern apes. No chimp or gorilla flakes stones in the wild: but an Orang utan has been taught to do so in captivity. Some Olduvai tools have been made from stones not present in the area and brought in from several kilometres away.
Was the implied cleverness of the early Homo reflected in the structure of his brain? Endocasts show that the brain was bigger in habilis, and that the enlargement was in the frontal and parietal areas. The sulci and gyri here resemble those of later man, and the speech areas are particularly prominent. The characteristic left right dominance is also present. But then we said both these factors were present in Australopithecus, so its not too surprising. Some experts see a linkage between tool making and speech via increasingly complex social behaviour.
How did these animals move? Well there is good evidence to show that they were bipedal, but in the small ones especially the arms were very long in relation to the legs. The hind limbs however are more modern than those of Australopithecus.
We should beware of thinking of Homo habilis as the great hunter however. They were not all that large and we have no evidence to support organised hunting. In primitive hunter/gatherer societies which survive today meat eating is usually associated with scavenging. There are tool marks on bones from Olduvai, but they are always superimposed on carnivore tooth marks. So they could be scavenging or extracting marrow from discarded carnivore kills. Habilis probably didn't have fire: uncooked meat is very tough given smallish teeth and jaws.
So how did they live? The classic idea of habilis society probably relies too heavily on human parallels, with sexual division of labour and much male camraderie resulting from co-operative hunting. Lets start from something more concrete. Food availability in this habitat was clearly spasmodic and uncertain as well as varied. Food sharing behaviour would clearly be an advantage in these circumstances, perhaps leading to provisioning of home bases, and perhaps the use of tools to make food containers. Think of the tremendous selective advantage of a bag in these circumstances.
We can also hypothesise that increasing brain size is linked with slower maturation and extended parental dependence. This might lead to a need for better offspring survival and perhaps to separate feeding ranges for males and females to avoid competition with the kids. Pair bonding would help too: if males feed females and infants as well as themselves the interval between pregnancies can be reduced.
But there are problems with this model: it posits human behaviour where none necessarily exists. Monogamous pair bonding correlates with reduced sexual dimorphism and habilis was markedly dimorphic. How do we know that the growth period was long? There aren't enough good fossils of habilis, but we know that in Australopithecus the growth period was rather short.
Perhaps habilis roamed around in large mixed sex groups with females bonding with individual males high in the pecking order (hence dimorphism) Perhaps again the divergence between Homo and robustus, or even between habilis and rudolfensis was due to diet. Robust forms could go for widespread, plentiful low grade food which they ground through in great quantities . More lightly built types could go for larger high quality items like meat, which would be in short, unpredictable supply and perhaps needed more wit to find. This would need better male female co-operation and perhaps leads towards monogamy and infant protection
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