Did modern humansevolve from Neanderthals or wipe them out? Olga Wojtas sifts the latest archaeological evidence
For almost the whole of this century, there has been a heated scientific debate about where modern human beings came from. One theory contends that modern humans evolved in a single area, subsequently spreading throughout the world and overrunning pre-existing populations, such as the Neanderthals. This theory is popularly known as "population dispersal". The second, conflicting, theory maintains that after an initial dispersal of hominids about a million years ago, modern populations evolved in parallel throughout Africa, Asia and Europe, making Neanderthals part of our ancestry. This is known as the "multiregional evolution" theory.
As a result of advances in genetic fingerprinting the debate has been dominated recently by molecular biology. Researchers led by the late Allan Wilson, professor of biochemistry at the University of California at Berkeley, have studied current patterns of mitochondrial DNA, which is inherited from the mother. Their discovery of key similarities across present day populations supports the theory that modern humans evolved from a relatively recent ancestor in a single area about 100,000 years ago and then dispersed.
Milford Wolpoff, professor of anthropology at the University of Michigan at Ann Arbor, queries this rate of genetic change, and suggests mitochondrial DNA springs from an ancestor at least a million years ago, whose descendants became the first hominids to populate Eurasia. Wolpoff is a leading champion of the multiregional evolution theory.
But the debate is now re-erupting through archaeology. Just as DNA technology brought genetics to the fore, new techniques for dating archaeological finds are allowing past evidence to be examined again. Until recently, archaeologists were dependent on radiocarbon dating, which can go back only about 40,000 years. But techniques such as thermoluminescence, electron spin resonance and uranium series now allow dating from 250,000 and even 500,000 years ago, by recording the effects of radiation in the soil and radioactive decay.
A leading proponent of the population dispersal theory, who has been closely involved in developing new dating methods, is Paul Mellars, reader in archaeology at Cambridge. He admits there is still controversy over the error margin of the techniques, but argues that if three effectively independent dating methods produce similar results for the same site, the dating can be seen as reasonably precise.
One dramatic shift has been the redating of anatomically modern human skeletal remains in Israel, previously presumed to be about 40,000 years old, and now shown to date from 100,000 years ago. This means that modern humans were established in the Middle East at least 50,000 years before they appeared in northern Europe and Asia, says Dr Mellars, and they therefore lived alongside Neanderthal and other "archaic" populations. The new dating also shows that a skull found in western France, generally seen as classically Neanderthal, is about 35,000 years old, at most 5,000 years older than nearby modern human, remains.
He argues that it is almost unthinkable that Neanderthals could have evolved into modern humans in such a short time unless they were effectively genetically swamped by an incoming population.
He believes that the 50,000 year delay before modern humans moved into Europe is partly because the Middle East was climatically similar to Africa, while much of Europe was still glacial tundra. But the modern humans then underwent a technological revolution which suddenly gave them the competitive edge over the Neanderthals, and helped them expand into the new glacial environment.
Archaeological findings show a much greater variety and complexity of stone tools, while highly shaped bone and antler tools, personal decorations and art objects appear for the first time. There are hints of strategy rather than opportunism in hunting, and more highly structured settlements, including huts.
Mellars believes there is a direct link between these behavioural changes and biological changes, with modern humans moving into the areas populated by Neanderthals.
"I think there is a dramatic contrast between Neanderthal and modern human behaviour. The Neanderthals look to me totally pragmatic, very good at making stone tools to butcher animals or cut wood, but they show no evidence of being concerned about appearances," he says.
"But when you get to modern humans, it looks as if they're trying to make a tool not only function for a particular job but conform to a particular appearance." Mellars supplies an intriguing theory for this shift: the appearance of developed language.
"If the Neanderthals had a notion but not a name, shape wouldn't matter. But a name goes with a mental image, and it's as though modern humans are saying 'this is an endscraper, I use it as an endscraper, I call it an endscraper and therefore it had better look like an endscraper'."
Since language does not fossilise, he admits that this theory can never be proved. But the elaborate art and ornamentation, such as perforated animal teeth and decorated bone tools, suggest a visual symbolism which would be a likely corollary of language, he says.
The archaeological evidence provides a separate argument from the biological data for population replacement in Europe, because the changes are so abrupt they point away from evolution, he believes. Most European archaeologists support the population replacement theory, although there are varying views as to whether the incoming population exterminated the Neanderthals, or the Neanderthal population numbers dwindled and died out because of the modern humans' superiority in hunting.
But other academics, notably in the United States, strongly oppose the theory of population replacement. Mellars has another intriguing theory for their discontent: he suggests that the supporters of multiregional evolution are the products of non-confrontational 1960s flower power, and cannot bear the thought of mass extinction through an early example of colonial capitalist imperialism.
But, Geoff A. Clark, distinguished research professor of anthropology at Arizona State University at Tempe believes that the population dispersal supporters may be influenced, even unconsciously, by the unflattering picture of Neanderthals painted by French palaeontologist Marcellin Boule in 1909.
"His view that they were hairy, brutish, stupid and stooped, and basically very different from modern humans, is popular and very compelling."
Nobody has ever demonstrated that Neanderthals are a different species from modern humans, he says, and assertions that they are fail to take into account the variability likely in populations.
Professor Clark is editing a book, Conceptual Issues in Modern Human Origins Research, and has been translating a French paper listing supposedly unique Neanderthal characteristics, including retromolar spaces.
"This is a gap between the wisdom teeth and the vertical element of the mandible, and is very commonly found in modern Europeans. I have retromolar spaces. Does that make me a Neanderthal?" Underlying the debate is a failure to consider epistemology, how we know what we think we know about the past, he says. It is naive to treat the patterns on retouched stone tools as if these were intrinsically meaningful, particularly as they are universal, appearing, for example, in Japan about 10,000 years ago.
Former French scholars created basic analytical units, such as Aurignacian, Mousterian and Chtelperronian, from specific stone tools, but given that the Aurignacian industries, for example, cover more than 20,000 years and several million square miles, these cannot represent the former distribution of peoples, tribes, ethnic or linguistic groups, he says.
Professor Wolpoff remains equally unconvinced by Mellars's theories. "I highly respect Paul Mellars, but this particular argument is as full of holes as a Swiss cheese. What he has done is equate biology and culture," he says. He objects to a distinction between Neanderthals and modern humans, and argues that either every contemporaneous group, or none, should receive the "modern" label. "You can't judge people by the way they look, just as you can't today. You judge them by what they do. And there are no grounds for saying one is more modern than another."
There is no anatomical reason why the Neanderthals were incapable of speech, he insists. And ornamentation and hut dwelling are a feature of the so-called Chtelperronian industries found in certain Neanderthal sites. "If this is a criterion of language, the Neanderthals must have been able to speak. You can argue about the biology till the cows come home, but the archaeological evidence shows us Neanderthals are capable of modern behaviour."
Wolpoff believes that the Neanderthals were evolving through intermixing with different populations, not more modern populations, just as the Mongol invasions resulted in a population which was a mixture of Asian and native European.
Mellars denies that he has been judging by appearances, and stresses that he holds an open mind on whether the Neanderthals were mentally inferior or different. But if the population dispersal theory is correct, and Neanderthals and modern humans evolved separately, it is plausible that their brains were different.
And given that his hypothesis has the last Neanderthals coexisting with the earliest modern humans in Europe, he finds the Chtelperronian example not so much unsurprising as essential.
"If the Chtelperronian didn't exist, we'd have to invent it," he says. "The Neanderthals were expert flint workers, and if they saw somebody making a blade, they could copy it. There are a few simple bone tools at one site which are not normally found in any other Neanderthal context, and a number of perforated animal teeth which look for all the world like personal ornaments.
"You could use that to argue that they had all the same mental capacities, but I think that's a gross overinterpretation of the evidence. The Neanderthals didn't do these things anywhere else, and it's possible to copy a pattern of behaviour without fully appreciating its meaning, or without it being a real pattern in your culture. The other interpretation is much simpler, that they managed to beg, borrow, steal or copy a few perforated teeth."