Lower and Middle Pleistocene - Homo erectus and Homo sapiens

Dr. D.R.Johnson

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.

The 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.
The usual estimate of the great ice ages was five: but this is based on data from the land, and each glaciation tends to mess up the record of the one before. Data from the sea bed show at least 12 glacial phases.

Homo erectus
The first Homo erectus fossils are from Africa, from our old friend Lake Turkana. These are 1.8-1.6 mya, getting perilously close to habilis and rudolfensis and indeed causing some confusion when they appear as isolated bits and pieces. These animals are large brained (800 -850ml) with a wide neurocranium and vault walls vertical in their lower parts, so that the back of the head is arched rather than bell shaped. There is a well marked area for the attachment of neck muscles and a nuchal ridge. There is a well marked brow ridge. The face is short and flat with light zygomatic arches. The palate is small and the cheek teeth reduced.

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.

Java
Outside Africa for the first time we see Asian erectus in Java and near Peking. In fact the first finds of this species were in Asia. The first was at Trinil on the Solo river in Java. Dubois recovered the top of a cranium , a femur and some teeth . The teeth proved to be that of an Orang but the skull cap had a brow ridge and nuchal crest and Dubois was struck by the contrast with the modern-looking femur and called the bits Pithecanthropus erectus, the erect ape man. The exostosis is pathological. There is nothing to associate the femur and the skull. They were found on a bend of a large river, where much rubbish would accumulate, 400m apart. The femur is old, but probably not contemporary with the skull. Both specimens are abraded, indicating a river journey, and no other remains were found in the vicinity. Ironically Dubois probably got the right idea, an erect advanced body with a rather primitive head, from probably incorrect evidence.

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.

China
The earliest Chinese erectus is from Lantian a much battered upper vault which closely resembles some Javan specimens and dated c0.7mya. The best material, however, comes from a deep gorge at Zhoukoudian (ZKD) near Peking or Beijing. Here a deep cleft in a vertical cliff face has been systematically excavated since the 1920s. Most of the specimens were lost in WW2, but are well known from casts. Most of the material is cranial, but there are faces and jaws and some teeth and postcranial bones. The crania are similar to the Javanese material with extensive nuchal area, brow ridges mid-sagittal keeling. Cranial capacity is rather higher (915-1225ml) reflected by higher vaults and wider frontals. The crania are generally less massive than the Javanese specimens.

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.

Further development of H.erectus
During the later Middle Pleistocene (0.2-0.5mya) we find more and more erectus material, more and more widely distributed. It tends to be fragmentary in parts, but all looks the same or similar. We find man for the first time in Africa from Morocco Ethiopia, Zambia, Kenya, Tanzania through to S Africa. We find him in Java, China and India. We perhaps find him in Greece and Spain in Germany, France, Hungary and even in England but

Homo sapiens
Amongst these widespread human remains we begin to find specimens which could be erectus, but which could also be sapiens. The more complete show similarities with erectus: cranial capacities may overlap, the vault bones are thick, the face is large and projecting and the brow ridges well developed.

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
Lower Pleistocene evidence is still confined to Sub-Saharan Africa. At first the old favourite sites, Olduvai, Lake Turkana dominate, but these are gradually joined by other sites in Kenya, Ethiopia and South Africa. The sites tend to be more extensive than those from the end of the Pleistocene and contain more artefacts, suggesting longer and more dense occupation. There is also greater site diversity, with some sites concerned with manufacture of tools (factory sites) and others with the disarticulation of large carcasses (butchery sites) as well as those less clearly identifiable (occupation sites).

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.

Homo habilis
At the end of the Pliocene and the beginning of the Pleistocene (2-1.4mya) Africa was crawling with hominids. Australopithecus robustus and A boisei were still to be found. But also there were 'non-robust' hominids about, some no bigger than Lucy, some larger. Cranial and dental features of these non-robusts are regarded as the first members of the genus Homo and are frequently classified as Homo habilis - handyman.
Early Homo fossils are known from E and S Africa but most evidence comes from Olduvai Gorge in Tanzania and Lake Turkana in Kenya. The evidence is rather fragmentary and raises some problems

Olduvai Gorge.
At Olduvai in 1960 Leakey found parts of an immature individual including a mandible with dentition two parietal bones, most of a foot and a clavicle, which may or may not belong to the same individual.

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.

Lake Turkana
Meanwhile at Lake Turkana hominid fossils were being recovered from the Koobi Fora formation, about 2mya. A large number of fossils turned up here including A boisei. But alongside these are other animals.

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.

South Africa
Early Homo material is also known from the Transvaal. Again these crop up in the same deposits as Australopithecus These animals however are distinct and very like some of the Olduvai material. Stw 53, the most complete skull recovered, for example closely resembles OH24, Twiggy, but with slightly more robust muscle markings.

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
The overall problem that we have with habilis, once we have decided that he is not an Australopithicine, is the diversity of the fossils. . In the Olduvai material this was interpreted by Leakey as diversification towards two later types of man H.erectus (who we haven't yet met) and H. sapiens. Others suggested that later material was more 'advanced' (although the time scale means that evolution was going at a fair old whack). If in doubt, blame it on sexual dimorphism was also used. The problem was made worse when the Lake Turkana finds were added, because they increased the sample size without decreasing the variability - in fact they tended to increase it. After a period in which specimens were either attributed to Australopithecus, or to Homo but without a species or just left to gather dust while we have a think some conclusions started to emerge. One obvious split was between 1813 look alikes and 1470 look alikes, with other fossils placed in one or other group. Were they species or were they sexes? The differences in cranial capacity between these two are so great that if they were due to sexual dimorphism it would have to be more marked than that seen in Gorilla, which holds the prize at the moment. So how about two species? The technique that you will be using in Practical 3 allows us to distinguish between size related shape change (i.e. the change in shape that is consequent on growth) and non-size related shape change. If you do this on early Homo fossils you find that they have lots of both kinds of shape change, well in excess of sexual dimorphism again, so it was proposed that two species were present. One of these, less variable than the other, with thinner vault, smaller parietals, a U shaped dental arch and smaller jaws was considered to be H habilis, and the rest were Homo sp. Later workers have split Homo sp. into four distinct groups. This was not too popular for obvious reasons, and many authorities now consider Homo sp to be Homo rudolfensis (Lake Rudolph was the old name for Lake Turkana).

Phylogeny
So here at the border of the new genus Homo and the old Australopithecus we see arguments at two levels. First was Homo habilis Homo or Australopithecus and secondly is Homo habilis one group, or two or more?

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.

We can summarise the main points of this argument

1. The earliest Homo material is so variable that it is likely to represent more than one species
2. Craniofacial data shows differences between habilis and rudolfensis. Rudolfensis seems to parallel robust Australopithicines.
3. Postcranial remains associated with habilis show that it had a primitive, Australopithicine-like postcranial skeleton. If the postcranial bits of rudolfensis are in fact rudolfensis (and there is doubt) then rudolfensis had a postcranial skeleton much more like Homo.
4. This is confusing : an advanced head on a primitive body or vice versa? Neither is necessarily ancestral to man.
5. Two animals so different have probably not had a recent common ancestor.

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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