An archaeologist who argued last week that modern man migrated from Africa much earlier than believed is now setting out to prove the crucial role that the Arabian Peninsula played in humans' dispersal across the globe.
"It is a remarkable fact that, until now, nobody has looked at what I believe is the pivotal part Arabia played in the overland migration of humans," said Michael Petraglia, 49, the co-director of the Centre for Asian Archaeology, Art and Culture at Oxford University.
"The focus has always been on [human migration via] the Levant. But, over the next five years, I hope to establish a centre of excellence at Oxford that will work with colleagues in the UAE, Saudi Arabia, Oman and elsewhere on a project that will completely revise the 'out of Africa' theories." During his presentation at the British Festival of Science last week, the archaeologist sent ripples through the scientific community when he said there was evidence that challenged the generally accepted notion that modern man first began to move to other parts of the world from his African birthplace only 60,000 years ago.
Dr Petraglia said that the scientific dating of rudimentary rock tools - mainly scrapers and spear heads - found by him and his research team in India and on the Arabian Peninsula pointed to the exodus occurring at least 70,000 to 80,000 years ago and, perhaps, much earlier still. More than that, he argued that the geneticists' theory that humans had travelled by boats or, at least, followed the coastline to reach Australasia about 45,000 years ago, was wrong.
The tools Dr Petraglia uncovered were deep inland, mainly in the desert of Saudi Arabia, suggesting that humans had migrated on foot as they gradually moved away from Africa, establishing settlements in areas where, at the time, the climate and landscapes were much different. "You have to remember that there have been a lot of fluctuations in the Arabian environment over the past 125,000 years," he said.
"At one stage, there were lakes and rivers and a countryside where hunter-gatherers could flourish. Then it went dry, then humid again, and then dry. "The tools from the Middle Paleolithic period we found were all at sites where there used to be rivers or lakes. When the dry periods came, the human populations there either became extinct or moved on. "One thing that people find surprising is that, over the past 30 years, these tools have been found to be quite abundant on the Arabian Peninsula. Most people are simply not aware of the richness of archaeology in Arabia. One of my goals is to promote the wealth of pre-history evidence in the region."
Dr Petraglia hopes his work in Arabia will uncover fossilised skeletal remains that will prove modern humans settled in the area far earlier than currently believed. Geneticists have used DNA comparisons between 21st century humans and fossils found in Africa to develop their theory that migrations first began 60,000 years ago. Conclusive evidence that the tools Dr Petraglia uncovered were from a much earlier period came from a dig in India. The artefacts were sandwiched in volcanic ash from the Toba "super-eruption" that geologists can date accurately to 74,000 years ago.
Geneticists, however, are not yet ready to abandon their calculations, arguing that the tools could have been made by Neanderthals rather than modern humans. They also argue that the 15,000 years it took to travel from Africa to Australasia could only have been achieved in such a comparatively short time had our forebears travelled along coastal routes, not ventured inland. Dr Petraglia says that his finds, many of them hundreds of kilometres from the coast, argue against this."To prove this on the Arabian Peninsula is going to take a determined effort involving an inter-disciplinary approach and international co-operation," he said.
"What we want to know is what happened demographically in Arabia. The remarkable thing is that it is an area that has been ignored for so long by the scientific community. "The current theory is that they made a rapid sweep from Africa, as if they knew where they were going. There's an inference that they moved in boats, but there is no evidence for this. "When I go to India and Arabia, there's archaeological evidence everywhere in the interior basins. I work in the Arabian Peninsula and the Indian subcontinent - two crucial areas for us to understand migration. But not much field research has been done there."
However, Chris Stringer of the Natural History Museum in London remains unconvinced by Dr Petraglia's finds, primarily because no modern human fossils have been found in Arabia or India. "There's no doubt that modern humans were in the Middle East [Levant] between about 90,000 and 120,000 years ago," he said at the science festival. "After 90,000 or 80,000 years ago, we lose sight of those modern people in the area, and instead we find Neanderthal fossils. The general interpretation is that those moderns came out briefly and then died out or went back.
"There are no fossils associated with them anywhere in India or Arabia, so we don't know whether they were modern humans. "The genetic data is strongly against the idea that the early dispersal is the one that gave rise to later modern people. Most of the calibrations suggest that the out-of-Africa event that gave rise to the recent peoples was about 60,000 years ago. "If Mike Petraglia is right and the early dispersal got as far as India, they still represent a failed dispersal because they didn't get any further than that," Prof Stringer said.
"These are important regions for future research and his discoveries are important even if I might disagree with some of the details of the interpretation."