In this week's issue of Science, I write about an ancient DNA study (also published in the journal) which concludes that farming was brought into Europe by immigrants rather than by the spread of farming technology, that is by demic rather than cultural diffusion. The issue has been debated for decades, and no doubt will continue to be debated despite this new evidence. But it is a fascinating study. Here are some excerpts from my story, which, like the paper, is available only to those with online access to Science (although the abstracts can be viewed.) First, the background:
About 11,000 years ago, farming began to replace the hunting-and-gathering lifestyle in the Near East. At first, agriculture spread slowly into Europe via modern-day Turkey, Greece, and Bulgaria. But about 7500 years ago, farming suddenly took off in central Europe, spreading in just a handful of centuries from an epicenter in Hungary and Slovakia to as far east as Ukraine and as far west as France. Rectangular houses sprang up, surrounded by cow pastures and fields of wheat and barley. Researchers have long debated whether this agricultural explosion was sparked by massive migrations of farmers themselves, so-called demic diffusion, or by the spread of farming ideas, known as cultural diffusion.
The basic findings:
The new study goes much further by fully sequencing ancient mtDNA from the skeletons of 25 early farmers as well as from 20 hunter-gatherers, thus allowing for direct comparison of the two ancient groups. The bones were previously unearthed at sites in Lithuania, Poland, Russia, and Germany and are dated from about 15,000 years ago to 4300 years ago. The team found that the mtDNA sequences of the farmers were so genetically distinct from those of the hunter-gatherers that they could not be related. For example, hunter-gatherer skeletons featured a high incidence of two genetic markers, called U4 and U5, which were not found in the farmers, and farmers harbored markers N1a and H, which were not found in the hunter-gatherers. Thus, the first farmers were immigrants who did not immediately mate with the locals.
Some researchers raise concerns about contamination of the ancient DNA samples, which is a chronic problem, although ancient DNA labs take considerable precautions to avoid it. The next step:
... the researchers say, is to find where those immigrant farmers came from. Burger and Pinhasi are already looking for freshly dug skeletons in western Turkey and southeastern Europe.
CREDIT: IVONNE MÜHLEIS, LANDESAMT FÜR DENKMALPFLEGE, BADEN-WÜRTTEMBERG
Even earlier Europeans. Like many others, I reported on the redating of two sites in Spain where handaxes, the Swiss Army knife of the Paleolithic, were found. The earlier of these dates, 900,000 years, nearly doubles the earliest known date for handaxes in Europe. This has all sorts of implications which I won't go into here; the link is free for four weeks from publication.