Not Out of Africa
Alan Thorne's challenging ideas
about human evolution
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Anthropologist Alan Thorne
holds casts of two of the skulls that have fueled a controversy about how and
when early man reached Australia. The delicate skull at right, of a hominid
known as Mungo Man, predates the larger, thicker skull on the left by tens of
thousands of years, a reversal of expectations that has challenged
traditional theories of evolution.
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She came to him in 1968, inside a small,
cheap suitcase
— her burned and shattered bones embedded in six blocks of calcified sand. The
field researchers who dug her up in a parched no-man's-land in southeastern
Australia suspected that she was tens of thousands of years old. He was 28.
Almost every day for the next six months, he painstakingly freed her remains
from the sand with a dental drill, prizing out more than 600 bone chips, each
no larger than a thumbnail. He washed them carefully with acetic acid, sealed
them with a preservative, and pieced them together into a recognizable
skeleton.
Looking closely at skull fragments, bits of
arm bone, and a hint of pelvis, he became convinced that two things were true.
First, the bones were human, Homo sapiens for sure, and they had held
together a young woman. As he assembled this "monster three-dimensional
jigsaw puzzle," Alan Thorne, then a lecturer in the department of anatomy
at the University of Sydney, began asking himself whose bones they might
actually have been. He had no idea that many years later, the answer to that
question would rock the world of anthropology.
Something else about this woman became clear early on— she had been important and powerful. The pattern of burn marks on her bones showed that after she died, her family burned the corpse, then smashed the bones. Later, they added more fuel and burned the bones a second time. This was an unusual ritual. Ancient Aboriginal women were typically buried without fuss. Thorne wondered if her descendants had tried to ensure that she did not return to haunt them; similar cremation rituals are still practiced by some Aboriginal groups today. As hours and days and months passed, he found himself thinking of her as a living, breathing person who'd spent her life encamped on the shores of Lake Mungo, in New South Wales. If this Mungo Lady turned out to be as ancient as field researchers thought, she would be the oldest human fossil ever found in Australia. To Thorne she was already the most mysterious.
In 1968 most anthropologists thought they had a grip on human evolution: Big-browed, thick-skulled humanoids had descended from walking apes. These hulking creatures were eventually replaced by the more advanced, fine-boned humans of our species— Homo sapiens. Throughout Australia, anthropologists had found only big-browed, thick-skulled fossils. That made Mungo Lady a puzzle. Lab analysis of her remains suggested she was 25,000 years old— old enough to be a grandmother to those specimens— but her skull bones were as delicate as an emu's eggshell. Thorne began to realize that she might be telling him a different story than the one he'd read in textbooks— that the delicate, fine-boned people had reached Australia before the big-brows.
That was an exotic thought, and now, many years later, it is fueling the debate within anthropology over a single huge question: Where did Homo sapiens come from? Most researchers accept a theory referred to as "out of Africa." It holds that numerous species of hominids— beginning with Homo erectus— began migrating out of Africa almost 2 million years ago and evolved into several species. Then a new species called Homo sapiens evolved in Africa and migrated between 100,000 and 120,000 years ago to Europe, Asia, and Australia, consigning all the earlier hominids it encountered to extinction.
Thorne preaches a revolutionary view called regional continuity. He believes that the species his opponents insist on calling Homo erectus was in fact Homo sapiens, and that they migrated out of Africa almost 2 million years ago and dispersed throughout Europe and Asia. As he sees it, there was no later migration and replacement: "Only one species of human has ever left Africa, and that is us."
Why does this matter? Because if Thorne and his camp are right, much of what we think we know about human evolution is wrong. In the world according to Thorne, the human family tree is not divided into discrete species such as Homo erectus, Homo antecessor, Homo heidelbergensis, and Homo neanderthalensis. They are all Homo sapiens. Yes, Thorne agrees, from the outside all these hominids look different from each other, but so do humans today— a Korean, a Nigerian, and a Dane hardly resemble each other. Our ancestors displayed great variety, but they were similar in the only way that mattered: They were the same species, which meant they could have sex with each other and produce fertile offspring.
Mungo Lady started Thorne down the road to regional continuity. Six years after he reassembled her, Thorne and three assistants unearthed another small-boned skeleton only 1,600 feet from where she had been found. At burial, this body had been laid on its right side, knees bent, arms tucked between its legs. Certain features— the skull, the shape of the pelvis, and the length of the long bones— told Thorne he was looking at Mungo Man, which thrilled him. As a general rule, female skeletons are more delicate than male ones, so doubts about the uniqueness of Mungo Lady's delicate bones would be quashed by having an equally delicate male counterpart to study.
Thorne's colleagues took their best guess at this specimen's age, as they had with Mungo Lady in 1968, based on radiocarbon dating and analysis of stratigraphy. They dated him to 30,000 years ago. As the oldest humans ever found down under, the finds were considered so important that the Australian government declared the sandy, bone-dry crater that was once Lake Mungo a national park in order to honor— and protect— the site. To the Aboriginal tribes, the pair became precious symbols of their early peopling of the continent.
But Thorne assigned a meaning to the bones that resonated beyond Australia. To his mind, the presence of two such unusual skeletons suggested that the peopling of the Pacific was a richer, more complex process than anyone had ever imagined. Anthropologists had long assumed that the first Homo sapiens to reach Australia were fishermen who left Indonesia and got blown off course, ending up on the new continent. Thorne began to wonder whether the first journey from Indonesia to Australia was not an accident but an adventure, undertaken with confidence by intelligent, mobile people. Mungo Lady and Mungo Man closely resembled skeletons of people living in China at the same time. Had these people migrated in boats to Australia? Had there been successive waves of immigration by different peoples over tens of thousands of years? To imagine such things, Thorne had to abandon familiar notions of early man as a blundering primitive.
He had already begun to do so. In the months he'd spent piecing together those braincases, he had begun to think of them as his elders, worthy of respect, capable of thought and imagination. That supposition was not an outrageous one for an Australian anthropologist to make. From childhood Thorne had grown up on a continent that was home to one of Earth's oldest continuous cultures. He'd learned a great deal about Aboriginal culture while working his way through college as a reporter at the Sydney Morning Herald. From where he stood, the ways of Mungo Man and Mungo Lady were not so different from those of modern Aborigines. He could easily picture two different tribes settling near Lake Mungo, one from nearby Java, another perhaps with roots in China. And once the two parties were encamped around the lake, it was not hard to imagine them crossbreeding.
Those who believe in regional continuity tend to have a view of sexuality that is more generous and more inclusive than that of the out-of-Africa proponents. In the latter view, Homo sapiens led a kind of search-and-replace mission as they spread around the planet; these researchers believe that members of the new species would not have been able to successfully reproduce with members of earlier species, no matter how hard they tried. Thorne thinks that's nonsense. "European scientists have dominated this field for 150 years," he says. "And they've got a big problem in Europe. Namely, they've got to account for those Neanderthals. My opponents would say that Cro-Magnons"— humans identical to us who lived during the Ice Age— "simply 'replaced' Neanderthals with no intermingling. That's the part I object to. 'No intermingling.' Now, I ask you, does that sound like the human beings you know?"
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.
Dueling Theories
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Graphic
by Matt Zang
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In 1997 Thorne finally got the tool he needed to explore Mungo Lady and Mungo 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.
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 nucleus— and 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.
When the first Neanderthal studies were published in 1997, Thorne had already retired. He had traveled the world for 30 years, excavating sites and filming science documentaries for Australian television. His face and his ideas were as well known in Australia as Carl Sagan's once were in the United States. At the request of the Aboriginal council, Thorne 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.
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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.
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. It's easy to contaminate specimens: More than once, scientists have been embarrassed when the "ancient DNA" they extracted turned out to be their own. To avoid this catastrophe, Adcock alone handled the specimens. He alone traveled between two testing labs. He sampled his own DNA and Thorne's to use as a control. Before sampling the ancient specimens, he tested five modern human and animal bones to make sure he'd perfected handling techniques. Then 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 analyzed, he reported only three contaminations. Ten of the 13 yielded DNA.
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.
The findings were published in January 2001 by Adcock, Thorne, and five other researchers. What followed was intense disagreement. "People just fell over when they read this new stuff," says Alan Mann, an anthropologist at Princeton University and a moderate in the human-origins debate. "The people at Mungo were totally modern looking and were expected to carry the DNA we have, but they didn't. I think that makes for an incredibly complicated story. It's a stunning development."
Thorne's critics were underwhelmed. "Alan is great at generating media interest. He's a former journalist, you know," says Chris Stringer, head of human origins at the Natural History Museum in London, a staunch advocate of the out-of-Africa model who is accustomed to his phone ringing off the hook every time Thorne fires another volley. "He has done some important work. I'm not saying his work is bad or wrong or whatever. Obviously, I have a different interpretation of it."
Stringer and his colleagues laid into Thorne. First, they said it was unlikely that 10 of the 13 skeletons had yielded mtDNA. This was an unprecedented success rate, so they believed that there had to be contamination. Even researchers at Oxford University, in one of the world's finest labs, had contaminated specimens. Then they said that mtDNA lines died out all the time; the Australians were making much ado about nothing. This part was 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.
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. Modern Aborigines didn't inherit Mungo Man's mtDNA, but they have certainly inherited the characteristics of his skull. "Eventually, all these people intermingled, and that's why the Aborigines have such diversity," he says.
Stringer, for his part, maintains that the out-of-Africa model could account for a settlement in southern Australia 60,000 years ago. Africans, he says, would have had to travel only one mile toward Australia each year for 10,000 years to make that possible. In other words, the Homo sapiens who left Africa 100,000 years ago would have reached Indonesia with plenty of time to sail to Australia.
In New York, Ian Tattersall, one of Thorne's closest friends, has long quibbled with his stance. "We've agreed to disagree," says Tattersall, curator of anthropology at the American Museum of Natural History. "I have a lot of respect for him; I just think he's barking up the wrong tree." Tattersall argues that Neanderthals were so obviously a separate species that Homo sapiens could not have bred with them.
Thorne says his lifelong study of animals has taught him otherwise. In captivity, for example, jaguars have mated with leopards and pumas and produced fertile female offspring— although all three animals supposedly belong to different species. Polar bears and brown bears, wolves and coyotes, dromedaries and Bactrian camels also cross-mate. Darwin himself dismissed species as a term that is "arbitrarily given, for the sake of convenience."
In recent months Thorne and his team have examined every human fossil from Australia and Asia they could get their hands on. They're retesting their Mungo Man work, hoping to confirm the findings and fill in some of the remaining gaps in the fossilized man's mtDNA profile. To satisfy their critics, they are allowing three rival labs to analyze Mungo Man extractions. Results will be available by the end of this year. When they are, they will most likely be debated. This science is still too inchoate for either side to declare victory.
Whatever the outcome, the bones from Lake Mungo have created change in Australia. The nation has committed to returning Lake Mungo and its environs to the Aborigines. Soon elders of the tribes living around Lake Mungo will decide when they will assume management of the land, artifacts, wildlife, and tourist trade. In 1991, standing near the metal stake that marks the spot where Mungo Lady was found, Thorne returned her bones to the elders of those tribes. At the time, elders debated whether to rebury her or preserve her. Thorne argued for the latter. "If you do away with her bones," he told them, "I'll always be right. You won't be able to refute my work. Someday there will be an aboriginal Alan Thorne, and he'll have a different way of looking at these bones. You have to give him that chance." The council voted for preservation. Today Mungo Lady inhabits a safe that can be opened only with a key, of which two copies exist. Aboriginal elders hold one; Thorne was presented with the other.
Despite Thorne's proselytizing, only a small fraction of the world's anthropologists accept his theories. But he couldn't care less. These days, he draws inspiration from the old Sherlock Holmes maxim: "Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth."
He points out that regional continuity is by far the simpler theory and can much more comfortably account for all the complicated twists and turns in the genetic evidence of human evolution now coming to light. "It argues that what is going on today is what has been going on for 2 million years, that the processes we see today are what have been going on in human populations for a very long time. You don't need a new species that has to extinguish all the other populations in the world. This is why out-of-Africa is the impossible, and regional continuity is not only not improbable but the answer and the truth."
From Discover Magazine
@ http://discovermagazine.com/2002/aug/featafrica
For more information about human origins see http://nexusilluminati.blogspot.com/search/label/out%20of%20Africa%20debunked
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