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Not Out of Africa but regional continuity A challenging idea about Human Evolution by Alan Thorne
1970 speculation
In the early 1970s these ideas were pure speculation. Thorne had no proof of anything. The bones had told him what they could and then lapsed into silence. So he tucked them away and went on with his career. Three decades later, the bones spoke again.
1997 mitochondrial DNA
In 1997 Thorne finally got the tool he needed to explore Mungo Lady and Man further. European scientists reported that they had successfully extracted fragments of mitochondrial DNA (mtDNA) from the remains of Neanderthal skeletons unearthed in Germany, Croatia, and Russia. This was stunning science, the Neanderthals had died out 35,000 years ago, and yet researchers had been able to harvest genetic matter from their bones as if they'd expired yesterday.
All living humans had their roots in Africa
It was the beginning of a revolution in paleoanthropology. Geneticists were hooking up with bone men everywhere. They were focusing on mtDNA because the mitochondria, which lie outside the nucleus, are easier to study in a human cell there are only 37 mitochondrial genes compared with 100,000 genes found in the nucleusóand because it is the only DNA anyone has been able to isolate and interpret in ancient fossils. For reasons not yet understood mtDNA survives the ravages of time better than nuclear DNA. And it has another interesting attribute: It's inherited only through the maternal line. Scientists seized upon this characteristic to try to build genetic family trees. Almost two years ago, geneticists working in Sweden and Germany reported studying the mtDNA of 53 living people from around the world. Within this small sample, they found that Africans shared a characteristic sequence of mtDNA, and that everyone else carried at least some portion of that sequence in their cells. The research suggests that all living humans had their roots in Africa. But Thorne doesn't put much stock in this report. He thinks the conclusions are questionable because samples taken in Africa today could be from people whose ancestors were not African.
New tests ordered
When the first Neanderthal studies were published in 1997, Thorne had retired but at the request of the Aboriginal council, he still safeguarded the Mungo fossils. Because three more sophisticated dating technologies were now available, he ordered new tests on 13 of the individuals in his care, and the results gave him a shock.
Mungo Man was 60,000 years old
The ages came back first. Using the new technologies, his team found that the small-boned Mungo Lady and Mungo Man were actually 60,000 years old twice as old as anyone had guessed. Thorne saw these dates as a crushing blow to the Out-of-Africa theorists. No matter what his opponents said, there wasn't enough time on their 120,000 year clock for Homo sapiens to leave Africa, dash up to China, evolve from rugged Africans into small-framed Asians, invent boats, sail to Australia, march to the interior, get sick, and die. How much simpler everyone's life would be, he thought, if anthropologists could agree that some of the players in this drama had reached China 1.5 million years ago and continued to evolve there
mtDNA of same 13 individuals
After the dating, Gregory Adcock, a doctoral student in genetics at Australian National University, decided to check all 13 fossils for mtDNA. But first he set up stringent procedures to avoid contaminating the specimens and he alone handled the specimens. Once he'd perfected handling techniques, he drilled into each fossil and took a sample from the bone's interior, where no one could ever have touched it. Of more than 60 samples he analysed he reported ten of the 13 had yielded DNA.
His mtDNA signature was unique
The results were nothing less than remarkable: Among the 10 successful extractions was the world's oldest known human DNA plucked from none other than Mungo Man. (No DNA was recovered from Mungo Lady, perhaps because she had been cremated.) Mungo Man also appeared to mock the findings of previous scientists: His mtDNA signature did not match anyone's, living or fossil, on Earth. There was no evidence that he was genetically related to ancient Africans.
Cat amongst the pigeons
Adcock, Thorne, and five other researchers published the findings in January 2001. What followed was intense disagreement amongst scientists because as the people at Mungo were totally modern looking they were expected to carry the DNA we have, but they didn't.
Chris Stringer
Chris Stringer, head of human origins at the Natural History Museum in London, a staunch advocate of the Out-of-Africa model had a completely different interpretation of the findings. He said it was unlikely that 10 of the 13 skeletons had yielded mtDNA. This was an unprecedented success rate, so he believed that there must have been contamination of the samples. Then he said that mtDNA lines died out all the time which is partly true: Twenty-five to 30 percent of mankind's mtDNA has been lost over the past million years when women gave birth to boys or didn't reproduce at all.
Modern Aborigines didn't inherit Mungo Man's mtDNA
Thorne concedes that mtDNA has evolved greatly over time, and all scientists working in this area have to be cautious. But as long as everyone is using mtDNA analysis as a basis for speculation he asks why his work is regarded with such suspicion. Mungo Man and his alternative complement of genes were alive enough to make it to Australia and contribute to the peopling of a continent. Modem Aborigines didn't inherit Mungo Man's mtDNA, but they have certainly inherited the characteristics of his skull.
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