NEW YORK – By sequencing DNA from several ancient individuals in the Maghreb region, researchers have linked the transition from foraging to food production in northwestern Africa to the arrival of individuals from Iberia and the Levant, who appeared to introduce agricultural approaches that were quickly adopted by local populations.
"Our results solve the puzzle of introduction of first agriculture and then pastoralism in the Early and Middle Neolithic, and the ensuing mixing of distinct genetic groups by the Late Neolithic," co-senior and corresponding author Mattias Jakobsson, a human evolution researcher affiliated with Uppsala University and the University of Johannesburg's Palaeo-Research Institute, said in an email.
There has been an ongoing debate over the transition to agriculture in the region, Jakobsson explained. While there are archaeological hints that local groups had contact with European farmers, leading to similar pottery and domestic animal use, other evidence suggests groups with a long history in northwestern Africa developed farming before interacting with Neolithic Europeans.
For their new analysis, appearing in Nature on Wednesday, the investigators combined genomic sequencing with archaeological clues, radiocarbon data, and detailed chronological analyses to retrace the human migrations and interactions that prompted Neolithic populations in northwestern Africa to shift from a hunter-gatherer lifestyle to farming and, more recently, pastoralism.
With genome sequence data for nine individuals at four Upper Paleolithic/Epipaleolithic, Early Neolithic, and Middle Neolithic sites in Morocco, reaching average coverage depths of 0.2-fold to nearly 46-fold, the researchers saw population genetic continuity stretching back some 8,000 years before the Neolithic farming transition in northwestern Africa, along with signs of genetic isolation in the Maghrebi population lineage.
The genetic and archaeological data suggested that local groups in northwestern Africa quickly adopted farming practices introduced by incoming Europeans during the Early Neolithic, despite limited initial mixing with the migrants.
"[C]ultural and technological knowledge appear to have been transferred mainly from European Neolithic farmers to local groups … whereas genetic ancestry flowed only from local groups to the incoming farmers," the authors explained.
On the other hand, ancestry from the Levant only turned up during a transition to pastoralism in the Middle Neolithic. By the Late Neolithic, the researchers reported, the region was home to individuals with ancestry from Maghrebi, Neolithic European, and Levant groups.
Based on these and other results, the authors suggested that "various waves of migration and admixture into northwestern Africa during the Neolithic possibly resulted in a heterogeneous economic and cultural landscape in the region — a mosaic of groups that included incoming farmers from Iberia, foragers adopting farming practices, and eastern pastoralists admixing with local people."
Even so, Jakobsson cautioned, "we don't know much about what happens after that during the Bronze Age." He noted that there may have been additional transitions and migrations that will be revealed in future studies that include genetic material from individuals residing in the region at that time.
"To disentangle the events during these migrations and the events prior to the migrations, the archaeogenomic tool kit is extremely valuable," he said.
In a corresponding news and views article in Nature, Louise Humphrey, a researcher with the Natural History Museum's Centre for Human Evolution Research in London, and Abdeljalil Bouzouggar, an investigator at Morocco's National Institute of Archaeological Sciences and Heritage, noted that the new study "points to a more complex and dynamic pattern of human migration and admixture than previously recognized in Morocco."
"After a prolonged period of at least 7,000 years of continuity and isolation, the genetic and cultural landscape of Morocco changed drastically between 7,500 and 5,700 years ago, with the arrival of Neolithic groups and lifestyles from both Europe and the Levant," they explained, adding that "the picture might become yet more nuanced as further genomic data are retrieved and analyzed."