Waves of grain: new data lift old model of agriculture's origins.

A new analysis of the locations and ages of ancient farming sites reinforces the controversial idea that the groups that started raising crops in the Middle East gradually grew in number and colonized much of Europe, replacing many native hunter-gatherers in the process.

Hunter-gatherers in some European locales may have adopted farming rather than surrender their home territories to the newcomers. Overall, though, the data indicate that newly arrived farmers reproduced at a rate high enough to keep their boundary moving steadily northwestward at roughly 1 kilometer per year, say anthropologist Ron Pinhasi of Roehampton University in London and his colleagues.

One of Pinhasi's coauthors, Albert J. Ammerman of Colgate University in Hamilton, N.Y., proposed much the same scenario more than 30 years ago with Stanford University's L. Luca Cavalli-Sforza. Their wave-of-advance model rested on an analysis of 53 farming sites.

Pinhasi's team considered the geographic arrangement of 735 farming sites that previous radiocarbon measurements had dated to between 11,000 and 5,000 years ago. The researchers calculated the most likely paths by which farmers who started out in any of 10 possible Middle Eastern spots would have traveled into Europe.

"I was surprised at how well the wave-of-advance model holds up with a much larger data set," Pinhasi says. "It took more than 3,000 years, or 100 generations of people, for the [agricultural] transition to reach northwestern Europe."

The new analysis, published in the December PloS Biology, indicates that agriculture spread in a widening are from an area that encompasses parts of modern-day Syria, Turkey, and Iraq.

If agriculture had taken root primarily through the adoption of cultivation techniques by people already living in Europe, the model would have depicted a much faster spread of farming settlements, Pinhasi's team contends.

In contrast, other researchers remain convinced that agriculture expanded primarily by the spread of cultivation techniques and year-round settlements among native Europeans (SN: 2/5/05, p. 88). The latest evidence for this perspective appeared in the Nov. 11 Science.

For that report, a team led by anthropologist Joachim Burger of Johannes Gutenberg University in Mainz, Germany, examined mitochondrial DNA, which is passed to offspring only from the mother. The researchers isolated this type of DNA from the bones of 24 adults who died in central European farming villages about 7,500 years ago. One-quarter of these individuals displayed a mitochondrial-DNA pattern that rarely occurs in modern Europeans. That pattern would be more common today if that early population had made a substantial genetic contribution to today's Europeans, the researchers contend.

If early farmers who moved into Europe didn't reproduce in large numbers, then native groups must have picked up the slack, Burger and his coworkers conclude.

Other DNA studies, including previous analyses of Y chromosomes in European men today, suggest that early Middle Eastern farmers had a substantial genetic impact in Europe, Pinhasi notes.

These conflicting DNA data may reflect intermarriage of immigrant farmer males with females native to Europe, suggests anthropologist Alex Bentley of the University of Durham in England.

Although he is sympathetic to the wave-of-advance model, archaeologist Peter Bogucki of Princeton University suspects that further research will show "a much more complicated combination of very rapid [agricultural] advances with long standstills."