jueves, 24 de abril de 2014

Anatomically Modern Humans leave Africa 130,000 years ago

Anatomically modern humans spread from Africa to Asia and Europe in several migratory movements according to new research by a team led by University of Tübingen’s Professor Katerina Harvati.
The study is published in the online Early Edition of the Proceedings of the National Academy of Sciences and shows 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.

Challenging the single dispersal scenario

By examining and testing different hypothetical dispersal scenarios, as well as taking into account the geography of potential migration routes, genetic data and cranial comparisons, the researchers found that the first wave of migration out of Africa must have started earlier than previously thought, taking place as early as the late Middle Pleistocene – with a second dispersal to northern Eurasia following around 50,000 years ago.
Most scientists agree that all living humans are descended from a common ancestor population which existed between 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 decided to investigate the out-of-Africa model of a single dispersal, against the potential for multiple dispersals of anatomically modern humans by comparing modern human crania from different parts of the world, neutral genetic data, and geographical distances associated with different dispersal routes.
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.
Supportive of a multiple dispersal model
“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.

More fine tuning

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.

Source: Past Horizons: http://www.pasthorizonspr.com/index.php/archives/04/2014/anatomically-modern-humans-leave-africa-130000-years-ago

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