The technological and other innovations associated with these
developments would seem to have given the modern human populations the crucial adaptations that were necessary to expand from Africa and to colonise a range of new and alien environments, and to rapidly expand their range over most areas of Asia and Europe
By Syed Akbar
Scientists world over believe that modern humans had dispersed from
Africa into Eurasia about 60,000 years ago. But they are not sure what
had forced them to leave Africa after living there for about 1,00,000
years.
Modern man evolved about 1,60,000 years ago in the African continent
and of this, he had spent about 1,00,000 years there. And suddenly he
started migrating from Africa about 60,000 years ago into Asia and
Europe.
A number of major technological, economic and social developments
in southern Africa between 80,000 and 60,000 years ago were
responsible for the dispersion of modern human beings to different
parts of the world, reveals a research study by Dr Paul A Mellars of the
University of Cambridge, UK.
Dr Mellars, who is the professor of prehistory and human evolution in
the department of archaeology at Cambridge, was in Hyderabad to
participate in an international workshop on "Human evolution and
disease". In his paper, "archaeological evidence for modern human
origins and dispersal," presented at the workshop, Dr Mellars based his
study on a number of recently investigated sites in South Africa.
"The technological and other innovations associated with these
developments would seem to have given the modern human
populations the crucial adaptations that were necessary to expand from
Africa and to colonise a range of new and alien environments, and to
rapidly expand their range over most areas of Asia and Europe," he
pointed out.
According to Dr Mellars, recent discoveries in India and Sri Lanka
show some striking similarities to sties in eastern and southern Africa,
which must be very close in time to the period when the first dispersal
from Africa took place, between 50,000 and 60,000 years ago. It would
seem that the further dispersal eastwards of these populations
throughout southern and south-eastern Asia was accompanied by a
progressive loss in the complexity of the associated technologies,
through a succession of repeated demographic and cultural founder
effects, leading to the comparative simplicity of the earliest Australian
technologies.
It is known that populations that were essentially modern in both
genetic and anatomical terms had already emerged in Africa by at least
1,50,000 years ago but it is not clear why did it take these populations a
further 1,00,000 years to disperse to other regions of the world?
Another question that has been haunting scientists is what were the
crucial evolutionary and adaptive developments that allowed these
populations to colonise a range of entirely new and alien environments
and to successfully compete with, and replace, the long-established,
and presumably well adapted, archaic populations in these regions?
It is interesting to see that two separate approaches to the analysis of
mtDNA (mitochondrial DNA) patterns in present-day African lineage
point strongly to an episode of rapid population growth in the ancestral
Africa populations centered broadly within the time range from 60,000
to 80,000 years ago, i.e., some 1,00,000 years after the inferred most
recent common ancestor of mitochondrially modern populations in
Africa.
Clearly, the precise age of these inferred population expansions
depends on the accuracy of the assumed mutation rate of mtDNA, but
the evidence as a whole points strongly to a major and apparently rapid
increase in African population numbers much earlier than that
experienced in either Asia or Europe and apparently involving
expansion by means of a demographic "diffusion wave" from a
relatively small population nucleus (probably confined to a fairly small
region of Africa) to other parts of the continent.
The central question is what could have caused this apparently dramatic
expansion in African populations between 60,000-80,000 before
present, and it is here that recent archaeological research in southern
and central Africa becomes central to the interpretation of the
demographic data.
The most relevant evidence at present comes from a number of sites
located close to the southern tip of Africa in Cape Province, most
notably from Blombos Cave and Klasies River on the southern coast
and those of Boomplaas Cave and Diepkloof, further to the north and
west.
Dr Mellars points out that the excavations at these sites revealed "soft
hammer" techniques of flaking; new forms of both specialised skin
working tools (end-scrapers) and tools for the controlled shaping of
bone and wooden artefacts (so-called burin forms); a range of
extensively shaped bone tools, apparently used as both tips of throwing
spears and sharply pointed awls for skin working; new forms of
carefully shaped stone inserts, probably used as tips and barbs of either
hafted throwing spears or conceivably wooden arrows; large numbers
of perforated estuarine shells, evidently used as personal ornaments of
some kind; and large quantities of imported red ochre, including two
pieces from the Blombos cave with carefully incised and relatively
complex geometrical designs on their surfaces. These designs represent
the earliest unambiguous forms of abstract "art" so far recorded.
Equally significant in these sites is the evidence for the large-scale
distribution or exchange of both high-quality stone for tool production
and the recently discovered shell beads from the Blombos cave, in both
cases either transported or traded over distances of at least 20-30 km.
All of these features show a striking resemblance to those which
characterise fully modern or "Upper Palaeolithic" cultures in Europe
and western Asia, which first appeared with the initial arrival of
anatomically and behaviourally modern populations at about
45,000-50,000 BP (before present) i.e., some 20,000 years later than
their appearance in the African sites.
Moreover the total population numbers in Africa decreased
significantly at this time, owing to the onset of extremely dry
conditions in many parts of Africa between 60,000 and 30,000 BP.
"The point is simply that increased levels of technological efficiency
and economic productivity in one small region of Africa could have
allowed a rapid expansion of these populations to other regions and an
associated competitive replacement (or absorption) of the earlier,
technologically less "advanced," populations in these regions," Dr
Mellars argues.
The pivotal question, of course, is what caused these radical changes in
the technology, economy, and social patterns of African groups about
80,000-70,000 BP, asks Dr Mellars.
He says the emergence of distinctively modern patterns of culture and
technology was due to a sudden change in the cognitive capacities of
the populations involved, entailing some form of neurological
mutation.
"Or alternatively (and more prosaically), we could look for an
interpretation in terms of some major shift in the adaptive and selective
pressures to which the human populations were subjected, perhaps
precipitated by some major episode of climatic and environmental
change. In this context, the obvious candidate would be the sharp
oscillations between wetter and drier climatic conditions that marked
the transition from oxygen isotope stage 5 to stage 4, as reflected in the
deep-sea core and ice-core climatic records," he says.
The final, and most controversial, issue at present is exactly when and
how these anatomically and genetically modern populations first spread
from Africa to other parts of Asia and Europe. Here there are two main
possibilities. According to Dr Mellars, the first is that the initial
expansion occurred via North Africa and the Nile valley, with
subsequent dispersal to both the west into Europe and to the east into
Asia. The second is that the initial dispersal was from Ethiopia, across
the mouth of the Red Sea, and then either northward through Arabia or
eastward along the south Asian coastline to Australasia-the so-called
"southern" or "coastal" route.
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