A team of researchers led by
the University of Tübingen's Professor Katerina Harvati has shown that
anatomically modern humans spread from Africa to Asia and Europe in several
migratory movements. The first ancestors of today's non-African peoples
probably took a southern route through the Arabian Peninsula as early as
130,000 years ago, the researchers found. The study is published by Professor
Katerina Harvati and her team from the Institute for Archaeological Sciences at
the University of Tübingen and the Senckenberg Center for Human Evolution and
Palaeoenvironment, in collaboration with colleagues from the University of Ferrara,
Italy, and the National Museum of Natural History, France. The study appears in
the online Early Edition of the Proceedings of the National Academy of
Sciences.
The Out-of-Africa model
that best fits both the genetic and cranial shape data. A first
migration along the Indian Ocean rim occurred as early as 130 thousand
years ago (green arrow) and was followed by a second, more recent
migration wave into Eurasia (red arrow).
Credit: Katerina Harvati/University of Tübingen and Senckenberg Center for Human Evolution and Palaeoenvironment
The scientists tested
different hypothetical dispersal scenarios, taking into account the geography
of potential migration routes, genetic data and cranial comparisons. They found
that the first wave of migration out of Africa started earlier than previously
thought, taking place as early as the late Middle Pleistocene -- with a second
dispersal to northern Eurasia following about 50,000 years ago.
Most scientists agree that
all humans living today are descended from a common ancestor population which
existed 100,000 to 200,000 years ago in Africa. The decreasing genetic and
phenotypic diversity observed in humans at increasing distances from
Sub-Saharan Africa has often been interpreted as evidence of a single dispersal
50,000 to 75,000 years ago. However, recent genetic, archaeological and
palaeoanthropological studies challenge this scenario.
Professor Harvati's team
tested the competing out-of-Africa models of a single dispersal against
multiple dispersals of anatomically modern humans. The scientists compared
modern human crania from different parts of the world, neutral genetic data,
and geographical distances associated with different dispersal routes.
Likewise, they reconstructed population split times from both the genetic data
and as predicted by each competing model. Because each dispersal scenario is
associated with specific geographic and temporal predictions, the researchers
were able to test them against the observed neutral biological distances
between groups, as revealed from both genetic and cranial data.
"Both lines of evidence
-- anatomical cranial comparisons as well as genetic data -- support a multiple
dispersal model," says Katerina Harvati. The first group of our ancestors
left Africa about 130,000 years ago and followed a coastal route through the
Arabian Peninsula to Australia and the west Pacific region. "Australian aborigines,
Papuans and Melanesians were relatively isolated after the early dispersal
along the southern route," says Hugo Reyes-Centeno, first author of the
study and member of the Tübingen team. He adds that other Asian populations
appear to be descended from members of a later migratory movement from Africa
to northern Eurasia about 50,000 years ago.
The researchers are confident
that continued field work and advances in genetics will allow for fine-tuning
of models of human expansion out of Africa. So far we can only speculate
whether, for example, severe droughts in East Africa occurring between 135,000
and 75,000 years ago prompted migration or had an impact on the local evolution
of human populations. The southern route region is a vast geographical space
that has been understudied by archaeologists and anthropologists, so future
work in this area will help support their findings.
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