A scientific team led by Harvard University in collaboration with the Institute of Evolutionary Biology, a joint center of Pompeu Fabra University (UPF) and the Higher Council for Scientific Research (CSIC), has carried out the first large-scale analysis of all the genome of ancient human remains from the Middle East. The results shed light on the genetic identities and migrations of the world's first farmers.
The study, published in the journal Nature, reveals three genetically distinct farmer populations that lived in the Near East in the early days of agriculture between 12,000 and 8,000 years ago: two groups just described in Iran and the Levant, and a group already known in Anatolia, in what is now Turkey. According to the results, it was the revolutionary agricultural technologies that spread throughout the region and not the groups of people who lived there.
"Some of the earliest agriculture was practiced in the Levant, including Israel and Jordan, and in the Zagros Mountains of Iran, border areas of the region known as Fertile Crescent," says Ron Pinhasi, associate professor of archeology at the University of Dublin. and co-author of the study. "We wanted to find out if these early farmers were genetically similar to each other or to the hunter-gatherers who lived there before, to find out how the world's first agricultural transition occurred."
This research turns the knowledge that was had to date about the genetic inheritance of the people who inhabit western Eurasia. According to the analysis, these seem to descend from four main groups: hunter-gatherers from present-day Western Europe, hunter-gatherers from Eastern Europe and the Russian steppe, the agricultural group from Iran and the agricultural group from the Levant.
"We have discovered that the relatively homogeneous population that today populates western Eurasia (Europe and the Near East), formerly consisted of highly structured groups of people, as different from each other as Europeans are today from East Asians. , "says David Reich, professor of genetics at Harvard Medical School (HMS) and a co-author of the study.
"As time passed, the populations of the Middle East mixed with each other and migrated to the surrounding regions to mingle with the people who lived there, until these initially very different groups became genetically very similar," adds Iosif Lazaridis , HMS genetic researcher and first author of the study.
The expansion of agriculture
Advanced ancient DNA technology enabled researchers to gather high-quality genomic information from 44 Middle Eastern individuals who lived between 14,000 and 3,400 years ago: pre-agricultural hunter-gatherers, early farmers, and their successors.
The study compared the genomes mentioned with those of some 240 ancient individuals from nearby regions and those of almost 2,600 people today. David Comas, IBE researcher and current director of the UPF Department of Experimental and Health Sciences, has participated in the analysis of the genomes of current people living in the Mediterranean area. “Comparing ancient DNA data with current data from Europe and the Middle East has allowed us to reconstruct the history of the ancestors of the human populations that occupied these territories. This comparison is essential since the populations that currently occupy a territory may not represent those that occupied it in the past due to the multiple migrations of our species ”.
The results have found that the early farmers of the Levant, Iran and Anatolia were genetically distinct. However, the farmers of the Levant and Iran were genetically similar to the early hunter-gatherers who lived in the same regions. These results suggest that agriculture spread across the Middle East because of people inventing or adopting agricultural technologies and not because of population replacement.
"Maybe one of the groups domesticated the goats and another started growing wheat, and the practices were shared in some way," says Lazaridis. "Each population contributed to some of the facets that led to the agricultural revolution and all of them bore fruit."
These findings tell a different story than what researchers believe happened later in Europe, when the first farmers migrated from Anatolia and replaced the hunter-gatherers who had been living there.
Mix and match
For the next 5,000 years, agricultural groups in the Middle East mingled with each other and with hunter-gatherers in Europe. "All that extraordinary diversity collapsed," Reich notes. "In the Bronze Age the populations had ancestors from many sources and but in general terms they resembled those of today."
Researchers have also been able to determine how the descendants of each group of first-time farmers contributed to the genetic ancestry of people from different parts of the world: related farmers from Anatolia spread across western Europe, those from the Levant moved east. From Africa, Iranians went north into the Russian steppe, and Iranian farmers and steppe hunter-gatherers spread to South Asia. According to Pinhasi, the Near East was the missing link for us to understand many human migrations. "
Finally, the study offers some more clues about a hypothetical and even older population called the “basal Eurasians,” an early and divergent branch of the family tree of humans living outside of Africa, whose existence has been deduced by Lazaridis from from DNA analysis but whose physical remains have not yet been found. "Every group in the ancient Near East appears to have a basal Eurasian ancestry - up to about fifty percent in the early groups," Lazardis notes.
To the researchers' surprise, statistical analyzes suggest that basal Eurasians contain no Neanderthal DNA remains. Other non-African groups have at least 2% Neanderthal DNA. The team believe this finding could explain why West Eurasians have less Neanderthal DNA than East Asians, even though Neanderthals are known to have lived in western Eurasia.
"Mixing with the basal Eurasians may have diluted the Neanderthal ancestry of the West Eurasians who would have ancestry from ancient Near Eastern farmers," Reich says. "Basal Eurasians could have lived in parts of the Middle East without coming into contact with Neanderthals." Looking ahead, Pinhasi says they are "eager to study remains of the world's earliest civilizations, predating the samples analyzed in the study. The people everyone reads about in history books are now within our grasp. genetic technology ”.
Reference: Lazaridis, I. et al. Genomic insights into the origin of farming in the ancient Near East. Nature http://dx.doi.org/10.1038/nature19310 (2016) .Ecoportal.net