Ancient genomics: Mixed ancestry for medieval Swahilis

Medieval Swahili people had African and Asian ancestry; according to a study of ancient DNA published in this week’s Nature. The findings, which correspond with the region’s current cultural landscape, suggest that mixing has been ongoing on the East African coast for more than a millennium.

The Swahili culture of coastal eastern Africa combines features of African and Asian cultures. The spoken language, Kiswahili, is of African origin, whilst the predominant religion of Islam hails from Asia. Non-Africans arrived in the region by AD 900, and trade routes were established across the Indian Ocean, but the extent to which these early populations mixed is unclear.

Reich and colleagues sequenced DNA from 80 individuals from six medieval and early modern coastal Swahili stone towns, dated between AD 1250 and 1800, and one inland town postdating AD 1650; of these 80 datasets, 54 were used for further analysis. They found that medieval Swahili populations had large proportions of non-African and African ancestry. Non-African ancestors were mainly Persian male individuals, whilst African ancestors were mainly female individuals, and there was also a small genetic contribution from India.

The finds suggest that Asian and African people began mixing in eastern Africa at least a thousand years ago at multiple locations along the coast. This is consistent with the Kilwa Chronicle, which is the oldest history told by people of the Swahili coast. The circumstances of these interactions are uncertain, but at the time, East African groups were matrilineal.