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The latest research suggests Australia's Adam and Eve are not as old as we thought - and lived much richer lives than we suspected. Deborah Smith reports.
Fifty thousand years ago, a lush landscape greeted the first Australians making their way towards the south-east of the continent. Temperatures were cooler than now. Megafauna - giant prehistoric animals such as marsupial lions, goannas and the rhinoceros-sized diprotodon - were abundant. And the freshwater lakes of the Willandra district in western NSW were brimming with fish. But change was coming. By the time the people living at Lake Mungo ceremoniously buried two of their dead, 40,000 years ago, water levels had begun to drop.
A study of the sediments and graves at Lake Mungo, published this week in Nature, uncovers the muddy layers deposited as the lake began to dry up. Twenty thousand years ago Lake Mungo had become the dry dusty hole we know today, but 20,000 years before that it had been a refuge from the encroaching desert, the study shows. Families clustered around the lake left artefacts, 775 of which researchers used to determine that the number of people living there peaked between 43,000 and 44,000 years ago, with the first wanderers arriving between 46,000 and 50,000 years ago.
This treasure-trove of history was found by the University of Melbourne geologist Professor Jim Bowler in 1969. He was searching for ancient lakes and came across the charred remains of Mungo Lady, who had been cremated. In 1974, he found a second complete skeleton, Mungo Man, buried 300 metres away.
The comprehensive study of 25 different sediment layers at Mungo - a collaboration between four universities, the CSIRO, and NSW National Parks and Wildlife and led by Bowler - concludes that both graves are 40,000 years old.
This is much younger than the 62,000 years Mungo Man was attributed with in 1999 by a team led by Professor Alan Thorne, of the Australian National University. Because Thorne is the country's leading opponent of the Out of Africa theory - that modern humans evolved in Africa about 100,000 years ago and then spread around the globe - the revision of Mungo Man's age has refocused
attention on academic disputes about mankind's origins.
Badlands topography on the lunette to the south of the road across the lake to the "Walls of China"
Photo: Don Hitchcock
Dr Tim Flannery, a proponent of the controversial theory that Australia's megafauna was wiped out 46,000 years ago in a "blitzkrieg" of hunting by the arriving people, also claims the new Mungo dates support this view.
For Bowler, however, these debates are irritating speculative distractions from the study's main findings. At 40,000 years old, Mungo Man and Mungo Lady remain Australia's oldest human burials and the earliest evidence on Earth of cultural sophistication, he says. Modern humans had not even reached North America by this time. In Europe, they were just starting to live alongside the Neanderthals.
"At Lake Mungo we have a cameo of people reacting to environmental change. It is one of the great stories of the peoples of the world."
The modern day story of the science of Mungo also has its fair share of rivalry. In its 1999 study, Thorne's team used three techniques to date Mungo Man at 62,000 years old, and it stands by its figure. It dated bone, teeth enamel and some sand.
Bowler has strongly challenged the results ever since. Dating human bones is "notoriously unreliable", he says. As well, the sand sample Thorne's group dated was taken hundreds of metres from the burial site. "You don't have to be a gravedigger ... to realise the age of the sand is not the same as the age of the grave," says Bowler. He says his team's results are based on careful geological field work that was crosschecked between four laboratories, while Thorne's team was "locked in a laboratory in Canberra and virtually misinterpreted the field evidence".
Thorne counters that Bowler's team used one dating technique, while his used three. Best practice is to have at least two methods produce the same result. A Thorne team member, Professor Rainer Grun, says the fact that the latest results were consistent between laboratories doesn't mean they are absolutely correct. "We now have two data sets that are contradictory. I do not have a plausible explanation."
Two years ago Thorne made world headlines with a study of Mungo Man's DNA that he claimed supported his idea that modern humans evolved from archaic humans in several places around the world, rather than striding out of Africa a relatively short time ago.
Photo: Alan Thorne, New Scientist 22 Feb 2003
Other scientists have expressed scepticism. But Thorne's old age for Mungo Man was also regarded as evidence for his theory. Homo sapiens would have had to move pretty fast to get from Africa to NSW by 62,000 years ago.
Now, however, Thorne says the age of Mungo Man is irrelevant to this origins debate. Recent fossils finds show modern humans were in China 110,000 years ago. "So he has got a long time to turn up in Australia. It doesn't matter if he is 40,000 or 60,000 years old."
In 2001 a member of Bowler's team, Dr Richard Roberts of Wollongong University, along with Flannery, director of the South Australian Museum, published research on their blitzkreig theory. They dated 28 sites across the continent, arguing their analysis showed the megafauna died out suddenly 46,600 years ago.
The conclusion has been challenged by other scientists, including Dr Judith Field of the University of Sydney and Dr Richard Fullager of the Australian Museum, who point to the presence of megafauna fossils at the 36,000-year-old Cuddie Springs site in NSW.
Flannery praises the Bowler team's research on Mungo Man as "the most thorough and rigorous dating" of ancient human remains. He says the finding that humans arrived at Lake Mungo between 46,000 and 50,000 years ago supports the idea that 47,000 years ago was a critical time in Australia's history. There is no evidence of a dramatic climatic change then, he says. "It's my view that humans arrived and extinction took place in almost the same geological instant."
Bowler, however, is sceptical of Flannery's theory and says the Mungo study provides no definitive new evidence to support it. He argues that climate change at 40,000 years ago was more intense than had been previously realised and could have played a role in the megafauna's demise. "To blame the earliest Australians for their complete extinction is drawing a long bow."
Burin of silcrete from Lake Mungo, about 7 cm across.
All silcrete on the "Walls of China" was carried there by aborigines from the western side of the lake. There is no silcrete available on the eastern side of Lake Mungo.
This tool would originally have had a sharp point for making holes in leather, which has broken off, and the tool was then thrown away.
The tools are elegantly made, with the minimum of flakes being removed, and no evidence of retouching. They have been made by master craftsmen with total control of the material.
Photo: Don Hitchcock
Discovered at Lake Mungo in far west NSW in 1974, Mungo Man had been covered in red ochre during a burial ritual. The hands were interlocked and positioned over the penis. Mungo Man was found in the same area as the cremated remains of a female skeleton known by local Aborigines as Mungo Lady. Recent lab studies of this type have suggested that our most recent common ancestor lived less than 200,000 years ago in Africa.
Tuesday, 9 January, 2001, 16:35 GMT
Fossil challenge to Africa theory
Bone fragments were examined for ancient DNA
Australian scientists say analysis of the oldest DNA ever taken from skeletal remains challenges the theory that all modern humans can trace their recent ancestry to Africa.
Dr Alan Thorne, Australian National University The study is based on the 60,000-year-old so-called Mungo Man skeleton, which was unearthed in New South Wales in 1974, and nine other anatomically modern Australian individuals who lived 8-15,000 years ago.
The Australian National University team looked at the DNA found in the mitochondria of these ancient people's cells. mtDNA, as it is known, is inherited only from females and also mutates - errors appear - at a steady rate, meaning it can be used as a "molecular clock" to investigate human history.
But the Australian researchers contend that the DNA sequences isolated from Mungo Man's bones show him to have a genetic lineage that is both older and distinct from this line.
Given the undoubted modern appearance of Mungo Man, they argue, major doubt must now be cast on the so-called "Out of Africa" hypothesis in which all living people are said to be descended from a group of modern humans who left their African homeland no earlier than about 120,000 years ago.
Alternative explanation
"What our evidence shows is that the situation is much more complicated than any of these supporters of Out of Africa would have imagined," lead researcher Dr Alan Thorne said.
Dating has put the age of the Mungo Man remains at between 56,000 and 68,000 years
"They were arguing that because the earliest forms of this particular genetic sequence in living people was found in Africa, that meant that all people must have come from Africa.
"Well, logically, that's not true anymore because we now have an older form of indisputably modern human that comes out of Australia."
Dr Thorne, whose team have published their research in the Proceedings of the National Academy of Sciences, is a proponent of the alternative, multi-regional explanation for the emergence of modern humans.
This suggests that modern humans arose simultaneously in Africa, Europe and Asia from one of our predecessors, Homo erectus, who left Africa more that 1.5 million years ago.
"Modern humans didn't just come from one area, they came from all areas," Dr Thorne said. "We assert that when people began to leave Africa about two million years ago, they were the ancestors of all modern people and we don't think modern humanity emerged from one place later on.
European studies
"We simply say that here we have a form much older than anything found in Africa and there's no evidence that it, or the skeletal anatomy of the fossil that it comes from, ever had anything to do with Africa. In fact, the skeleton looks very much like slightly earlier fossils that we know were in China."
Dr Alan Thorne supports the multi-regional explanation for the emergence of modern humans
But Out of Africa supporters are not about to let go of their beliefs because of the Australian research. Professor Chris Stringer, from the Natural History Museum in London, UK, said that, given experience with European fossils, there was some doubt over whether DNA analysis of such old samples was reliable. And he said the research community would want to see the work repeated in other labs before major conclusions were drawn from the Australian research.
But even assuming the DNA sequences were correct, Professor Stringer said it could just mean that there was much more genetic diversity in the past than was previously realised.
There is no evidence here that the ancestry of these Australian fossils goes back a million or two million years
Prof Chris Stringer, Natural History Museum "What it says is that some of that genetic diversity has been lost today," he told BBC News Online. "This sequence could have been in Australia and in Africa. In other words, it might have been in Africa 200,000 years ago, [it] came out with some of the African people and then got lost.
"There is no evidence here that the ancestry of these Australian fossils goes back a million or two million years, which is the multi-regional prediction."
**********************************************The Bulletin, January 16, 2001
Ground-breaking DNA analysis of an ancient human skeleton threatens to shatter conventional theories of human origin. And, as Graeme O'Neill reports, lend weight to the controversial theory that Australia was populated, by not one, but two stone-age peoples.
Dead men do tell tales, none more intriguing than that of an ancient Australian whose bones lay for 60,000 years beneath the dunes fringing the southern part of Lake Mungo in south-western NSW. His tale has emerged from the oldest human DNA recovered anywhere in the world. And it represents the most serious challenge yet to the theory of an African "Eve", the idea that each of the 6 billion human beings on Earth is descended from one ancestor (seepage 30).
The online edition of the prestigious USbased research journal Proceedings of the National Academy of Science this week publishes the -results of a joint study by a team of Australian National University and CSIRO researchers, headed by a young ANU molecular geneticist, Dr Gregory Adcock.
In a breathtaking technological feat, Adcock and his colleagues have reconstructed the mitochondrial DNA - or mtDNA "fingerprint" of the ancient, but anatomically modern, human known as LM3, whose perfectly preserved skeleton was discovered in the dunes of Lake Mungo in 1974.
LM3's mtDNA signature is no longer found in humans, but the Australian team made a stunning discovery: it pre-dates Eve's.
"Eve", unlike her famous progenitor, the 3.5 million-year-old australopithecine "Lucy", left no fossil - she exists only as a genetic signature, reconstructed from a comparative analysis of mtDNA from modern humans.
Mitochondria are akin to batteries: they are microscopic structures that supply cells with biochemical fuel and carry their own small set of genes on a tiny loop of DNA, separate from the central repository of genes in the cell nucleus. Children inherit only their mother's mtDNA, unchanged except for occasional, random mutations. In the family tree of modern humans, all mtDNA branches were believed to stretch back, an estimated 100,000 years, to Eve.
Although LM3's age is still in dispute, three advanced dating techniques - uranium/thorium, electron-spin resonance and optically stimulated luminescence dating - have indicated an age between 52,000 and 68,000 years, with a likely age of 62,000 years.
Adcock and his PhD supervisor, ANU anthropologist Dr Alan Thorne, worked with two colleagues, Professor Simon Easteal and Dr Gavin Hutfley, and with CSIRO Plant Industry molecular geneticists DrJim Peacock and Dr Liz Dennis, and Dr Lars Jermiin of the Australian Genomic Information Centre at Sydney University.
They isolated the DNA of 10 human skeletons - four from the Willandra Lakes World Heritage Area near Balranald in south-western NSW, which incorporates Lake Mungo, and six from Kow Swamp, near Cohuna in northern Victoria.
The Eve theory, which has been in vogue for 14 years, implied that no modern human outside Africa, alive or dead, would have an older mtDNA signature than Eve herself. What odds, then, that one of the first mtDNA signatures to be recovered from an ancient Australian skeleton would be older than Eve's?
LM3 is at least 40,000 years younger than Eve. Desiccated blood cells from his bone marrow yielded overlapping, fragmented mtDNA that, when digitally reassembled with a Silicon Graphics supercomputer, revealed a signature both unique, yet oddly familiar.
Part of LM3's ancient mtDNA signature survives in a small minority of living human beings - not in their mitochondria, but inserted in one of their chromosomes.
Ever since humans and chimpanzees diverged from a common ancestor at least 5 million years ago, replication accidents have seen segments of mtDNA copied and inserted randomly into chromosomal DNAin the cell nucleus, the central repository of the human genetic blueprint.
MtDNA is more prone to replication errors than nuclear DNA, so it mutates much more rapidly. But when a copied mtDNA segment inserts into slow-mutating nuclear DNA, its rate of evolution slows to a crawl. Meanwhile, the mtDNA from which it was copied continues evolving at its original, frenetic rate. From these ancient mtDNA inserts, effectively genetic fossils, geneticists can reconstruct long-extinct mtDNA lineages.
In 1995, Professor Svante Pddbo and a colleague Hans Zischler, working at the Max Planck Institute for Molecular Genetics in Berlin, announced in the journal Nature they had discovered an mtDNA insert on chromosome 11. The insert is quite rare, but widespread in living humans around the globe, including Africans. Minor variations on the original theme revealed it is less than a million years old. Improbably, the extinct mtDNA lineage from which the insert was derived has now turned up in the skeleton of an anatomically modern Australian. After 60,000 years, LM3's bones have yielded up their astonishing secret to modern science.
In a time far beyond human memory or Dreamtime myth, LM3 had a real name and he was revered in death. His kinsmen had dusted or painted his body with red ochre before carefully burying him in the pale golden sand.
A small patch of pink-hued bone, recently exposed by heavy rain, caught DrJim Bowler's eye as he was 'I just tagging along an old horizon " in layered sediments at Lake Mungo in 1974, looking for extinct marsupial bones.
A stratigrapher, Bowler reconstructs and dates past environments from clues in layered sediments. Although he is not a paleontologist, he immediately recognised the ochre stained bone as the top of a human cranium.
Five years earlier, in 1969, the Melbourne University researcher had found a fragmented female skeleton in the Mungo dunes. The bones of the celebrated "Mungo Lady" yielded a radiocarbon age of around 24,000 years, nearly doubling the estimated time of earliest human occupation of the continent.
LM3's remains were found below the layer in which Bowler found Mungo Lady, making them more than 24,000 years old - but their real age would remain an open question for almost 25 years.
Radiocarbon dating is increasingly unreliable for dating materials older than about 30,000 years and effectively useless beyond 40,000 years. Contamination by younger carbon can make samples seem much younger than they really are.
The task of excavating the LM3 skeleton fell to a young ANU paleontologist, Alan Thorne, the senior author of the new paper. Thorne recalls his surprise on excavating the skeleton. Though clearly male, LM3 was like the Mungo Lady: he was hypergracile, that is, of an extremely slender build and his cranial vault had thin bones. A high, domed forehead, descending to a small, near-vertical face, imparted a strikingly modern appearance.
Physically, Mungo Lady and LM3 contrasted strikingly with six ancient skeletons Thorne had found several years earlier in sandy sediments at Kow Swamp. In these, the cranial vault was almost twice as thick as in any living human and a low sloping forehead with heavy brow ridges surmounted a jutting lower face. With their massive skulls and strikingly robust build, they appeared more primitive than the Mungo remains - yet they are much younger, with radiocarbon ages between 8000 and 15,000 years.
The Mungo and Kow Swamp skulls represent opposite extremes in a spectrum of variation visible in today's Aborigines - the differences between them, says Thorne, are greater than those that separate Europe's Neanderthals and the Cro-Magnon ancestors of modern Europeans.
After comparing the Australian skeletons with ancient human fossils from China and Indonesia, Thorne concluded that two physically distinct peoples - a "gracile" race from ancient China, and a "robust" race from Indonesia - had colonised Australia by sea in prehistoric times. The gracile skulls bore an uncanny resemblance to 30,000-year-old skulls found in two sites in north-eastern China, LiuJiang and the Beijing Upper Cave.
To Thorne, the robust race, represented by finds at Kow Swamp, Cossack in Western Australia and the WLH50 skull from Willandra Lakes, carry what his former anatomy teacher at the University of Sydney, Professor Neil Macintosh, called "the mark of ancient java". And Macintosh was referring not just to fossils, but to all living Aborigines.
Although more modern and less massive, the "robust" skulls resembled the 750,000year-old 'Java Man" skull found at Sangiran, Java. They were also strikingly similar to the skulls of the later Solo people of Java, his direct descendants, who are in turn the presumed ancestors of the Kow Swamp people.
Whoever reached Australia first, the "gracile" and "robust" races had somehow coexisted for millennia, just as Neanderthals and CroMagnons did in Europe some 40,000 to 28,000 years ago. By the end of the last glacial period, 10,000 years ago, Australia's populations had fused. If Thorne is right, today's Aborigines are their hybrid progeny.
The new study also isolated mtDNA from the Kow Swamp skeletons - remarkably, despite their archaic appearance, they carry the young signature of Eve's descendants.
Thorne challenges his opponents to explain why, when everywhere else in the world, there was an evolutionary trend from a robust to a more gracile skull and skeleton, the reverse could have occurred in Australia. In his view, a more likely explanation is that the Mungo and Kow Swamp skeletons represent different migrations of physically distinct people to Australia.
Even in Australia, Thorne's "two race" hypothesis remains controversial. His ANU colleague Dr Colin Groves and other Australian prehistorians contend that the "robust" crania are normal Aboriginal skulls artificially deformed by ritual binding, a common practice among many cultures around the world, even into the 20th century.
In 1977, at a major international conference on human evolution in the Kenyan capital, Nairobi, Thorne found a kindred spirit in US paleontologist Professor Milford Wolpoff of the University of Michigan.
Wolpoff was intrigued by Thorne's Centre and Edge paper, describing a process of continual, long-distance gene flow that may have allowed widespread early human populations to evolve modern features simultaneously.
Wolpoff's own comparative study of ancient Neanderthal skulls from western and central Europe had convinced him that certain Neanderthal traits persisted in living Europeans. One is the prominent, flared "de Gaulle" nose found in some French and Spanish people. This is believed to have been an adaptation by Neanderthals for warming and humidifying the frigid, dry air of a glaciated Europe. A narrow aperture in the side of the skull in some Europeans may also be a Neanderthal trait.
Wolpoff's conclusions accorded with Thorne's own radical idea that "archaic" human lineages from Asia left ripples that are still visible in the gene pool of today's Aborigines.
In 1981, Thorne and Wolpoff published a synthesis of their ideas, drawing upon comparisons of modern and ancient bones.
The "multi-region" hypothesis - now amended by Thorne to a more descriptive "regional continuity" hypothesis - proposes that modern human beings evolved simultaneously in different regions of the world and that they all contributed to the gene pool of modern humans. Despite their geographic spread, there was always some gene flow at the margins, a process that accelerated in the modern world.
There was particularly intense selection pressure favouring genes that influenced brain size and cranial capacity. Improved intelligence or memory underpin quintessentially human traits such as language, culture, social cohesion and behavioural flexibility. Even as regional populations developed unique physical characteristics in response to their environments, they were driven inexorably towards modernity.
But in 1987, a paper in Nature seemed to bury regional continuity. A radical new archaeology, relying on genes, not bones, offered a very different account of the evolution of modern human beings - and launched African Eve into international headlines.
The Eve theory, with its conclusion that no archaic human populations outside Africa contributed to the gene pool of modern human beings, is still the dominant paradigm, despite the methodology of the original study being fundamentally flawed.
Wilson's team began its analysis by rooting its hypothetical human mtDNA family tree in Africa, an assumption that permitted no other conclusion.
In 1997, Pddbo's research group recovered a mtDNA fingerprint from the Feldholer Neanderthal skeleton uncovered in Germany in 1865 - the first Neanderthal remains ever found. It was clearly older than that of Eve, as were other mtDNA signatures recovered from Neanderthal skeletons in Croatia and Russia.
Pddbo and Dr Chris Stringer of the British Museum of Natural History, a leading proponent of the Eve hypothesis, said the results supported the idea that Neanderthals did not contribute to the gene pool of modern humans.
The Australian researchers say this interpretation may not be justified: 'MtDNA is a small component of the total genome, and the failure of a mitochondrial lineage to survive to the present does not imply a similar failure for the remainder of the genome."
Thorne believes the major weakness of the Eve theory is that mtDNA signatures, which are transmitted only through the female line, can easily be lost - while ancient nuclear genes continue travelling through time.
"One of the things 1 have argued all along is that morphology and genes don't necessarily go together," says Thorne. "All males are mitochondrially extinct, yet our opponents argue that mtDNA and nuclear genes must go together."
If LM3 left any descendants, they would have inherited his mate's mtDNA signature, but his nuclear genes would survive. But, in the hypothetical case, his mate carried a new wave Eve mtDNA. Paadbo and Stringer would conclude that LM3 had not contributed to the gene pool of modern Aborigines.
As Thorne points out, unlike the situation in Europe, the consensus among Australian researchers is that all early humans represented in the Australian fossil record contributed to the gene pool of modern Aborigines.
A find in a cave in Portugal in 1999 offers tangible evidence that Pddbo and Stringer are wrong: a 27,000-year-old skeleton of a child that was clearly a hybrid between a Neanderthal and a Cro-Magnon.
But Colin Groves, an Eve proponent, counters: "I can't see for the life of me how this offers support for regional continuity."
Groves agrees with Simon Easteal that the most likely explanation is that a selective sweep late in human evolution saw Eve's superior mtDNA prevail, over all other ancient mtDNA lineages, because it provided more fuel for a big, energy-hungry brain.
"Here, we evidently have the survival of one of the more ancient lineages, which subsequently died out," says Groves. "It means the selective sweep was not yet complete [in Australia] and I wouldn't expect it to be."
Groves says it's "not improbable, just extremely interesting" that rare, ancient mtDNA lineages would persist for some time after Eve's signature began its sweep across the world.
LM3's mtDNA signature, he says, is not nearly as distinctive as the Neanderthal-signatures~ natures from Europe. "If a Neanderthal lineage turned up in a homo sapiens, that would be very unexpected."
Despite his scepticism about the conclusions of the new research, Groves is impressed with his colleagues' technical feat of recovering 60,000-year-old DNA, and the meticulous manner in which they ensured contamination by modern DNA would not produce a spurious signature. -
He believes the prospects are "very good" for recovering DNA from other, well-preserved ancient bones - including those of extinct animals. That prospect also excites Thorne, who believes Adcock has opened a new window on prehistory.
"Everyone thought there must be something special about cold wet caves in Europe, because the first three fossils found there all yielded DNA. But Lake Mungo is not a cold wet cave - it's open, dry and hot, and it's been that way for a long time.
"People who want to look at these sorts of issues, right across the biological spectrum, but especially in vertebrates, should go out and start to sample. It's possible they will be able to get DNA out of giant ground sloths, mammoths and other extinct megafauna - including things like Diprotodon [giant wombats] -here in Australia."