A new picture of humans' arrival in Europe.

Part. 2

Comparisons of modern human genomes with Neanderthals' suggest that some interbreeding occurred. But because Asians and Europeans have identical levels of Neanderthal DNA, geneticists presume that they are seeing the result of trysts that occurred before modern humans moved to Europe. Higham's work could help to pin down when and where humans and Neanderthals were most likely to have interbred.

He thinks that Neanderthals probably went extinct gradually. His work re-dating Neanderthal sites in Croatia⁸and the Caucasus⁹ suggests that Neanderthals disappeared from these regions by about 40,000 years ago. Other researchers say that the last Neanderthals may have eked out a living in the Iberian peninsula until as recently as 24,000 years ago¹⁰, although Higham and his former graduate student, Rachel Wood, have unpublished work that questions that timing.

Still, the part of Higham's work that has generated the most debate (or at least the most journal pages), involves the cognitive abilities of Neanderthals. Neanderthals may no longer be written off as knuckle-dragging brutes, but archaeologists disagree over whether Neanderthals were capable of the sort of symbolic representations that underlie language, art and religion.

Shell beads and other ornaments suggest that modern humans made symbolic objects as early as 100,000 years ago in Africa, and probably carried those traditions with them into Europe. Evidence that Neanderthals were capable of symbolic thinking comes partly from what is known as the Châtelperronian industry in central and southeastern France, which included ornamental objects such as perforated animal teeth, shell beads and ivory pendants. Neanderthal bones found alongside such artefacts at the Grotte du Renne in central France made the site “the flagship for the idea that Neanderthals had symbolic behaviour”, says Stringer.

Higham, however, questions how good that evidence is¹¹. His team dated animal bones, antlers and teeth from various layers of the cave. The dates for those in the Châtelperronian layers were all over the place, from 49,000 to 21,000 years old. Higham thinks that bones and artefacts from different periods have become jumbled, through a combination of geological tumult, excavation errors and shoddy record-keeping. He therefore doesn't think the Châtelperronian objects should be used to support symbolic thinking for Neanderthals.

João Zilhão, a palaeoanthropologist at the University of Barcelona in Spain, has emerged as Higham's staunchest critic. Last year, Zilhão and his colleagues pointed out that the artefacts in the Châtelperronian layer seemed to be in the right place and questioned whether Higham's team had managed to fully decontaminate the bone samples¹². “How come the bones move and the stone tools do not? It's impossible,” he asks. Higham struck back¹³, and Zilhão is now drafting another response. “This could go on forever and I've got no more time to spend on it,” says Higham.

Both say that their dispute is purely academic. They continue to work together on other material, and are open to collaboration on the Grotte du Renne controversy. “He's pretty easy to work with,” Zilhão says of Higham. “He speaks his mind, but so do I.–

Stringer says that the understanding of palaeolithic history is in flux. The dates that Higham and others are now generating may settle some long-standing debates, but they are also generating new questions. “Maybe you've got a muddying of the waters before they clarify and settle out,” Stringer says.

This summer, Higham will trek to the Denisova cave in southern Siberia's Altai Mountains, to try to make sense of its convoluted history. When Soviet scientists found the cave in the 1970s, they discovered Neanderthal tools and human remains there. But in 2010, DNA sequencing of a finger bone extracted from the cave pointed to the existence of a hitherto unknown population of archaic humans, called Denisovans¹⁴, who lived in the cave sometime between 30,000 and 48,000 years ago¹⁵. Higham thinks that his team can narrow down that range and perhaps determine whether Denisovans lived in the region with humans and Neanderthals.

Higham's grand vision is to develop a fuller, almost cinematic version of early human migrations. “We want to create this huge map that will allow us to try to look at the movement of people, the movement of objects, the development of new ideas. The big archaeological questions, really.” His team has already begun to play around with software capable of building such a map of Europe, some of which incorporates data from a stack of manuscripts on his desk that he hopes will be published over the next year and a half.

But if this film is to be more historical documentary than a period drama, it requires the sort of chronologies that Higham and his team are generating. “You have to know the dates,” he says.”

Nature 485, 27–29 (03 May 2012) doi:10.1038/485027a

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