© NASALake Toba, Sumatra bears the scars of a massive eruption 74,000 years ago. The question is: did modern humans arrive in Asia before or after this time?
The first anatomically modern humans almost certainly arrived in southern Asia within the last 70,000 years, having dispersed as small groups of pioneer settlers along coastal regions from Africa, say UK scientists.
But another expert has disputed their proposal, saying there is still too little evidence to say for certain how humans dispersed into the region.
Using a combination of genetic and archaeological evidence, scientists led by
University of Cambridge archaeologist Professor Paul Mellars and geneticist Professor Martin Richards, from the
University of Huddersfield, say modern humans left eastern Africa sometime after 70,000 years ago and dispersed along the coast to the region south of the Himalayas.
The research, which appears in the
Proceedings of the National Academy of Science , is the latest volley in a heated debate about how, and when, humans spread around the globe.
The controversy has been particularly intense when it comes to the southern part of the Asian continent, the authors say.
Some scientists think modern humans arrived in the region 50,000 to 60,000 years ago having originated as a small group who left Africa and expanded around the coastlines of southern and southeast Asia.
Others think there was a much earlier dispersal of modern humans from Africa sometime before a massive volcanic eruption on Mount Toba in Sumatra, about 74,000 years ago.
Genetic and archaeological evidenceThe latest paper tackles the question on genetic and archaeological fronts.
On the genetic side, Richards and colleagues analysed about a thousand whole-mitochondrial DNA genomes from India.
Mitochondrial DNA is inherited down the female line of descent, and can give scientists a very detailed and dated reconstruction of the maternal genealogy, Richards explains.
"The new mitochondrial DNA dating tells us that the ancestors of modern non-Africans from throughout the world lived in Africa until about 70,000 years ago, and had reached Arabia by around 60,000 years ago, and South Asia shortly afterwards."
From an archaeological perspective, Mellars and colleagues compared artefacts discovered in earlier and later Indian remains.
"These remains include bone tools, engravings and personal ornaments, as well as distinctive stone tools. They all appear first in Africa and then later in India, after around 50,000 years ago," says Richards.
According to Richards and Mellars, there is no evidence to support the idea that early modern humans colonised South Asia before the Toba eruption.
"All of the available evidence supports a much later colonisation."
"I think the evidence is now pretty decisive," Richards says.
'Riddled with problems'But Professor Michael Petraglia, an archaeologist from the University of Oxford disputes Richards' and Mellars' argument.
Petraglia says there's not enough evidence to rule out an earlier colonisation before the eruption of Mount Toba.
"The research reported by Mellars and colleagues is riddled with problems," he says.
Petraglia says that the similarity between tools used in Africa 60,000 years ago and those from Asia dating to around 35,000 years ago is not a consequence of direct migration.
"These toolkits are separated in time by more than 20,000 years and distances exceeding several thousand miles."
He questions the evidence supporting a migration along the coast. He says that surveys of ancient shorelines have not revealed any evidence for human settlements anywhere along the Indian Ocean shore between 55,000 and 50,000 years ago.
He also says genetic dating should be treated cautiously.
"Most geneticists will admit that genetic dating of the out-of-Africa event is tenuous, at best. Published genetic ages for out-of-Africa range anywhere between 45,000 to 130,000 years ago."
Stay tunedPetraglia says his team is currently conducting archaeological fieldwork in Arabia, India and Sri Lanka they expect will show that the story of human dispersal from Africa is complex.
"What we can agree on is that little research in these key geographic regions has been conducted and much more evidence needs to be collected to support or refute the different theories," says Petraglia.
That's a sentiment Richards shares: "In this subject there always seems to be room for debate, which perhaps is no bad thing."
humans.
Scientists are delving into the human brain seeking the origins of memory and consciousness. This seems somehow connected to recent events since the Neanders were famously claimed to not have been inventive. This advance was credited to the Cro Magnons who arrived sometime around 50,000 y ago.
Was the memory of past applicable to future acquired then? Yes.
The Neanders coped with the result of constant winter as a result of Toba. In Africa the humans endured radiation, ash fall, toxic gases which must have decimated the survivors.
We now know Lamarkian inheritance is more correct than genes. We know epi genetic tagging turns off gene expression for a generation and is suspected to operate milti generationally.
Consider: epi-tagging turns off, and if the brain was operational at the Neander level, then epi tagging turned off a brain enzyme that had a memory that primarily operated in the moment. We may expect that that was the optimal level. Not a 360 scope of past to future but present.
With this view we may realize that our comprehensive look back and forward is malfunctional and hinders the operation of the organism.
This is a radical view but when taking endless war based on individualism into consideration, it is a sane deduction. Because we live with a condition does not make it nature's choice. Our present predicament of individuality and constant change is not nature's choice but the result of a catastrophic environment that called for memory of past applicable to future.
In nature, this effect would turn off when the generational crisis had past but that seems not to be the case. That would imply that our world has degenerated into conditions which foster constant crisis.
I consider this theory to be possible due to the Second Law which forbids more organization to occur in a closed environment. I propose our environment of Sol's system closed by the Oort shell.
You might protest that our science is progressing but there is satisfactory evidence from past unexplained technology that equals or surpasses our own. Our size, our health, our years have all declined as in accordance with the Second Law.