Posted by Paul Rodgers 28 May 2008 Print version Listen RSS Where do we come from? Paul Rodgers charts some of the latest work exploring the movement and development of humans based on DNA and the full mitochondrial genome
Where do we come from? It’s an abiding question, and one that has been only partially answered by science. While little doubt remains that our species evolved in East Africa, details of its spread around the world are still obscure. And the further back we peer, the harder it is to get a clear picture.
What evidence we have falls into three categories: physical remains, such as stone tools and cave paintings, can reveal the movement of technology and culture, but sometimes these spread not just as groups move, but between peoples. Linguistic studies, comparing modern languages to find their common roots, have the same problem. But genetics, looking at how minor mutations have spread through the world’s population, does not.
One of the more intriguing suggestions in the past decade is that the initial spread of humans from Africa extended along the southern coastline of Eurasia, to what is now Southeast Asia, then a subcontinent called Sundaland that was twice the size of modern India, stretching from Burma to Borneo. The flooding of this fertile paradise as the last Ice Age ended forced these people to adapt to new lifestyles, flee to new lands, or become extinct.
DNA research led by Leeds University’s Martin Richards, one of only two professors of archaeogenetics in the world, supports this idea, showing that the stone-age people on the southeastern shore of Sundaland expanded across the newly formed island chains 12,000 years ago.
The new theory, published in the journal Molecular Biology and Evolution, is likely to draw bitter criticism from supporters of the old consensus, based on linguistics, that the area is populated today by descendants of a rice-growing people called the Austronesians who expanded from Taiwan just 4,000 years ago. “Some quite forceful archaeologists have been extremely reluctant to accept this,” says Professor Richards. “And I haven’t met a single linguist willing to give up the out-of-Taiwan argument.”
The Austronesians supposedly supplanted the indigenous hunter-gatherers, who first arrived 50,000 years ago yet were considered so insignificant that they have not even been named.
“That was a great mistake,” Professor Richards says. His team is the first to use the full mitochondrial genome rather than fragments, giving it a much more detailed picture of population movements in the distant past. Their results show that the biggest migration went not from Taiwan, but to it, and occurred much earlier.
“The radical explanation is that the linguists are wrong and that these people spread out during the last episode of post-glacial expansion,” he said. The Austronesians may have been like the Normans, a small elite group that arrived later and took control of a larger, indigenous population, he
suggests.
Sundaland was the biggest area to be drowned as the glaciers started to retreat 19,000 years ago, raising sea levels by more than 100 metres. The second largest, Doggerland, now the southern North Sea, was submerged towards the end of the Ice Age, separating the British Isles from continental Europe.
The people living in the southeast Asian subcontinent would have been particularly hard hit by three great sea level surges, 14,000, 11,500 and 7,600 years ago, believed to have been caused by catastrophic events as the ice sheets in North America and Antarctica retreated.
Professor Richards argues that many populations will have been wiped out as their land disappeared beneath the waves.
But one group could have been pre-adapted to the new environment, which had fewer inland plains and meandering riverbanks and twice as much coastline – the people of southeast Sundaland, who may have had a maritime culture linking them to the nearby Wallacean island group, named after the Victorian naturalist Alfred Russel Wallace, which includes New Guinea.
What is certain is that, as sea levels rose, these people began to spread throughout the region, according to mitochondrial mutations, which are passed down from mother to child. A parallel study of stone-age tools by other members of the team supports the theory, showing the spread of a stone tool technology called “flake and blade” throughout the region.
Professor Richards hopes to do further work on the Sundaland population, and is already working on a study of y chromosomes, which are only passed down through the male line. Marine archaeology could also shed more light on the drowned culture, though there are no immediate plans to begin looking beneath the shallow waters of the Sundaland Shelf.
In the original version of this article it was suggested the idea that Europeans are descended from a group of people who settled in what is now Southeast Asia, then a subcontinent called Sundaland, was mooted by Dr Stephen Oppenheimer in his 1998 book Eden in the East. We fully accept that this was not the case and apologise to Dr Oppenheimer for the error.
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