How food production entered sub-Saharan Africa some 5,000 years ago and the ways in which herding and farming spread through the continent in ancient times has long been a topic of archaeological debate. Now a study led by Stony Brook University, Saint Louis University and Harvard Medical School scientists is providing some answers to these questions.
Prehistoric rock paintings in Manda Guéli Cave in the Ennedi Mountains, Chad, Central Africa. Image credit: David Stanley / CC BY 2.0.
The first form of food production to spread through most of Africa was the herding of cattle, sheep and goats. This way of life — known as pastoralism — continues to support millions of people living on the arid grasslands that cover much of sub-Saharan Africa.
“Today, East Africa is one of the most genetically, linguistically, and culturally diverse places in the world,” said co-lead author Dr. Elizabeth Sawchuk, a bioarchaeologist at Stony Brook University.
“Our findings trace the roots of this mosaic back several millennia. Distinct peoples have co-existed in the Rift Valley of Kenya and Tanzania for a very long time.”
In the study, Dr. Sawchuk and colleagues analyzed genome-wide data from 41 ancient human skeletons, which were recovered from East African archeological sites and curated at the National Museums of Kenya and Tanzania, and the Livingstone Museum in Zambia, and which dated to the Later Stone Age, Pastoral Neolithic, and Iron Age.
“The origins of food producers in East Africa have remained elusive because of gaps in the archaeological record,” said co-lead author Professor Mary Prendergast, of Saint Louis University and Harvard Medical School.
“Our study uses DNA to answer previously unresolvable questions about how people were moving and interacting.”
Previous archaeological research shows that the Great Rift Valley was a key site for the transition from foraging to herding.
Herders of livestock first appeared in northern Kenya around 5,000 years ago, associated with elaborate monumental cemeteries, and then spread south into the Rift Valley, where Pastoral Neolithic cultures developed.
The new genetic results reveal that this spread of herding into Kenya and Tanzania involved groups with ancestry derived from northeast Africa, who appeared in East Africa and mixed with local foragers there between about 4,500-3,500 years ago.
Previously, the origins and timing of these population shifts were unclear, and some archaeologists hypothesized that domestic animals spread through exchange networks, rather than by movement of people.
After around 3,500 years ago, herders and foragers became genetically isolated in East Africa, even though they continued to live side by side.
Scientists have hypothesized substantial interaction among foraging and herding groups, but the new results reveal that there were strong and persistent social barriers that lasted long after the initial encounters.
Another major genetic shift occurred during the Iron Age around 1,200 years ago, with movement into the region of additional peoples from both northeastern and western Africa. These groups contributed to ancient ancestry profiles similar to those of many East Africans today. This genetic shift parallels two major cultural changes: farming and iron-working.
The study also provided insight into the evolution of lactase persistence, the ability to digest milk into adulthood, in East Africa. Although this genetic adaptation is found in high proportions among Kenyan and Tanzanian pastoralists today, it was rare among these ancient herders, contrary to previous predictions.
“Future archeological and ancient DNA research in the Turkana Basin, the Horn of Africa, and other parts of northeastern Africa will be necessary to confirm the earliest stages of the spread of herding into the region, and where the initial admixture between northeast African populations and East African foragers occurred,” the researchers said.
The study appears today in the journal Science.
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Mary E. Prendergast et al. Ancient DNA reveals a multistep spread of the first herders into sub-Saharan Africa. Science, published online May 30, 2019; doi: 10.1126/science.aaw6275
