Homo ergaster in Africa

The First Colonists: Expansion of Hominim Range

Distribution and Nomenclature● The designation of Homo ergaster is

relatively recent, and is intended to distinguish the early forms of Homo erectus from the later forms

● This has met with some resistance from specialists, for those that are opposed to this distinction see no justification for positing a different species

● Irrespective of the controversies amongst the palaeoanthropologists, there is evidence of a change in the anatomy and behaviour in the species that is considered by some as Homo ergaster

● Our earliest finds derive from East Africa, sometimes at the sites where Homo habilis was found in older layers

● It is clear that Homo ergaster/Homo erectus was an extremely successful species and was the first to colonise regions outside of Africa

Affixing the Age of Homo ergaster● Nevertheless, in this lecture we shall

consider the evidence only from East Africa, where this species presumably diversified from Homo habilis and explore the later diffusion inside Africa and into Asia in the following lecture

● The paucity of sites affording remains of Homo ergaster renders it difficult to determine the age range of this species

● It is, however, commonly thought to have flourished between 2.0 million and 1.6 million years ago

● Some have suggested that it is significantly younger, emerging only at 1.7 million years

● The dates from the site of Dmanisi in Georgia have affixed the occupation by Homo ergaster here to 1.88 million years, so presumably it must be older in Africa

Physical Characteristics● No agreement exists on which features

distinguish Homo ergaster from Homo erectus

● This renders the determination of this species rather arbitrary; hence the controversy regarding its status

● An enlargement of cranial capacity and a slightly smaller set of teeth does, however, distinguish Homo ergaster and early forms of Homo erectus from Homo habilis

● It is widely accepted that this form of hominim evolved out of Homo habilis, although there are some that select Homo rudolfensis as a probable direct ancestor

● We are able to study the inter-relationship of cultural behaviour and evolution with this species (and Homo erectus) better than with any other preceding hominim form because of the larger data-set but also the expansion of the range of settlement which implies certain social and technological features of culture

Cranial Capacity● Homo ergaster shows an increase in

cranial capacity (700-900 cm3) from that of Homo habilis

● The skull bones are thinner and lack an obvious depression, or sulcus, on the surface, which may be the most-distinguishing characteristic between Homo ergaster and Homo erectus skulls

● Also, the face of Homo ergaster is less robust (more gracile) than is that of Homo erectus

● Homo ergaster skulls also display increased cranial breadth across the parietal bones, as well as an increase in the length of the occipital bone

● A broadening in the nasal bones and nasal openings also can be seen

● Homo ergaster skulls also show a shorter cranial base and greater development of the mandibular symphysis

Dentition and Diet● The dentition of Homo ergaster is

similar to that of Homo sapiens, but the teeth of the former were slightly larger to that of the latter

● However, Homo ergaster shows some dental reduction when compared to earlier Homo species

● The interesting feature of Homo ergaster teeth is located on the backside of the incisors

● These teeth are ‘scooped’ in appearance and referred to as ‘shovel-shaped'

● Some scholars have suggested that such teeth constitute an adaptation for hunter-gatherers to process food, and this is indeed a distinguishing characteristic of the Native American populations

Locomotion and Stature● It is indisputable that Homo ergaster

was fully bipedal—the pelvis, joints and vertebral column demonstrate this

● This species was slightly taller than Homo habilis, but the small fossil sample renders it difficult to make any statements regarding diversity in size

● Altogether, the species is more gracile and was probably faster than Homo habilis

● The long arms of Homo habilis have vanished, and there is more proportion in the body, possibly a result of evolutionary adaptations associated with full bipedalism and also a greater endurance for long-range movement

● Rather than having the ability to run quickly, Homo ergaster seems better suited for walking long distances

Social Structure and Behaviour● We can be certain that Homo ergaster was

capable of producing fire, for this was a necessity in their expansion within and beyond Africa

● This undoubtedly began to accelerate the transformation of dentition, the digestive tract, and the range of foods that could be consumed

● Moreover, it may have also permitted a more developed social structure focusing on the hearth and the communal sharing and preparation of food

● Expansion of range also suggests slightly larger population numbers, perhaps even an adaptive advantage over Homo habilis in that this species never appeared to have colonised new territories

● A question of climatic change, too, is also relevant to the triggers for Homo ergaster expansion, but it is probable that social structure, technological innovation, and dietary flexibility were essential for the expansion to have been successful

Lithic Industry● After roughly 1.6 million years, a new lithic

industry emerges in Africa known as the Acheulean

● This refers to a tool-kit based on the production of bifacially manufactured handaxes

● Although a relatively simple type of tool to produce, it was highly practical and was distributed throughout the Old World and persisted until at least the end of the Middle Palaeolithic (ca. 35,000 BP)

● Its production implies a good grasp of causality, but also a sense of symmetry that can possibly be explained with reference to the development of mechanisms coordinating the function of the two sides of the brain, namely, a change in the frontal cortex

● This industry completely supplants the chopper industry in Africa, but the chopper industry continues to flourish elsewhere—in East Asia, handaxes do not occur at all

The Expansion of the Genus Homo

Movement in Africa and Onward to Asia

Dispersal of Homo● The diffusion of the genus Homo appears to have begun rapidly after its

emergence

● We have encountered evidence of Homo ergaster occupation at Dmanisi, in Georgia, already at between 1.88 million and 1.6 million years the former is the more likely date)

● Some suggestions of even earlier occupation in the Middle East, most particularly in Israel, have been adduced that would place this at roughly 2.0 million years

● Other studies at Riwat in Pakistan, and in China, have also provided early dates that situate the presence of Homo between 2.4 and 1.6 million years

● The earliest dates here, however, are profoundly controversial but it is difficult to dismiss them entirely on a priori grounds

● Although there is a relative increase in sites at 1.6 million years, this should not lead us to accept these dates as more reliable than the older sites in Eurasia and outside of East Africa

● It is clear that the Dmanisi and Trinil site (in Java) are likely older by at least 100,000 to 200,000 years

● Moreover, they are all based on choppers rather than the Achelean tradition which is consistent with early dates for dispersal

Dispersal in Africa● We must also bear in mind that the

diffusion of Homo occurred within Africa, as well as beyond Africa

● This must have occurred before the occupation at Dmanisi and elsewhere, at least for the north-east portions of the continent

● Almost nothing is, however, known about the expansion of Homo into Egypt and the dating of the putatively early sites in north-west Africa are wrapped in controversy

● Only an handful of sites older than a million years are known in the north of Africa

● Some debate also concerns the type of hominim that produced the African tools—the absence of fossil remains leaves this an unresolvable problem

Mechanisms of Expansion● A perplexing problem concerns the

mechanism of population expansion out of East Africa

● Numerous possibilities have been adduced:

1. Population rise

2. Reduction of available resources

3. Expansion of social territory

4. Wanderlust

● All of these are difficult, if not impossible, to prove or falsify through the archaeological record

● It is difficult to imagine a rise in population sufficient to compel population to move, but perhaps the answer lies in the perceived need for space

● The mechanism may have been access to better habitats, leading to expansion

Technology and Fire● A possible explanation for the gradual diffusion

of Homo is an advance in technological facility or an improvement of the environmental conditions which might have favoured colonisation

● Perhaps the most significant innovation that could have facilitated the expansion of population is the discovery of fire

● This would have permitted settlement in regions that would have been difficult and otherwise dangerous for Homo and was most certainly involved in the expansion to more temperate regions such as Georgia, Pakistan, China and also North Africa

● Less obvious are the advantages that might have been provided by the emergent Acheulean industry and other aspects of material culture

● It must, however, be considered that fire might have made spear tips harder and also permitted the consumption of foods that might otherwise have posed a digestive problem

Middle Eastern Possibilities● The passage to Dmanisi must have

been over the Middle East, but we do not have any reliable dates from sites in this region that place the expansion of Homo to roughly 2.0 – 1.6 million years

● Many sites affording chopper tools and Acheulean hand-axes have been nominated as potentially being from this time frame, but only Ubeidiya in the Jordan Valley of Israel has provided wholly reliable dates of being between 1.6 million and 1.4 million years

● Although obviously an important site, it is later than those known from Dmanisi and also Trinil in Java

● We cannot, therefore, adduce any evidence from the Middle East or, for that matter, North East Africa contemporary with the expansion of Homo

Dmanisi, Georgia● Perhaps the most spectacular discovery

from the Lower Palaeolithic has been the recovery of human remains and tools at the site of Dmanisi

● The dating of this site reliably places it between 1.88 and 1.6 million years, most authorities favouring the former as being likeliest

● This provided unequivocal evidence of early Homo migration into Eurasia, although there were numerous suggestions that this indeed occurred from the Chinese and Java specimens, although there has been persistent concern over the reliability of the dates of these

● The hominim remains here have been assigned to Homo ergaster, but in the tradition of many of the taxonomic debates, some have called it Homo georgicus

The Hominim Remains● The hominim remains from Dmanisi have

been regarded as belonging to Homo ergaster or Homo erectus, but the difficulties of distinguishing amongst the early Homo species is illustrated by some declaring these remains to represent Homo habilis

● It is clear that these are early Homo remains, which is why the designation of Homo ergaster was made

● If we regard Homo ergaster as an archaic form of Homo erectus, this is perfectly consistent with the dates and the process of expansion outwith Africa suggested by these

● It is, furthermore, consistent with the evidence from East Asia which all represent archaic forms of Homo erectus

● An absence of any specimens from Homo habilis in Asia, and indeed outside of East Africa, militates against this species beginning the colonisation process

Lithic Industry● The lithic industry from Dmanisi is

fascinating, as it consists entirely of a chopper based tradition cognate to the Oldowan tradition

● This suggests that the migration out of Africa occurred before the advent of the Acheulean tradition, which seems to have emerged at roughly 1.6 million years

● It is relatively primitive but clearly belongs to the Developed Oldowan industries encountered in East Africa

● We cannot postulate that this industry was pursued because of a lack of raw material suitable for the production of the hand-axes as it is no worse than material available at places such as Olduvai Gorge

● It is similar to the industries encountered elsewhere in Asia from this broad period and might reflect an insularity of the migrant population

Reduction Strategies● The choppers represent the most basic

reduction strategy—basic, but highly efficient

● Flakes were struck from the pebbles, creating sharp edges suitable for chopping or cutting material

● The flakes themselves were likely utilised as tools also but the antiquity of these specimens and there exposure to weathering in some of the deposits renders it impossible to apply micro-wear analysis on them to determine function

● Much ink was been spilt on discussions concerning what the reduction strategies imply about cognitive ability

● It is clear that they reflect a sense of symmetry, which is sometimes associated with the development of distinct activities in the different brain hemispheres

Symmetry and Cognition● In addition to the symmetry, which involves an

immense amount of motor co-ordination not seen in the implements produced by chimpanzees, there was an appreciation of causality manifested in the striking of different types of flake at different points in the reduction process

● Both fast and slow percussion were used, along with different force, to detach different types of flake to give the cores their distinctive symmetric shape

● This is not an innovation of Homo erectus/Homo ergaster, as a similar capacity is demonstrated in the industries of Homo habilis

● It nevertheless signals an advance in cognitive capacity that is clearly distinct from that seen in the earlier phases

● How much of this is cultural knowledge, and how much actually a change in brain structure ?

Ain Hanech, Algeria● A site that is roughly contemporary

with Dmanisi, but in northern Africa, is Ain Hanech

● The dating of this site is disputed, but some have situated it at roughly 1.9 to 1.7 million years

● It affords tools produced in the chopper tradition, which is again consistent with the migration of a population out of East Africa before the emergence of the Acheulean tradition

● The colonisation of North Africa would have involved the crossing of many different types of ecological zones, namely, jungle, desert and—most significantly—mountains

● Remains of equus have been recovered in association with the finds here