The Indian Ocean can be considered as a closed sea, an afro-Asiatic Mediterranean,1, 2
around which populations have migrated and mixed. In contrast to the Atlantic Ocean, which was a formidable natural barrier to East–West migration, the Indian Ocean with its seasonal monsoon winds favoured such exchanges, and most of the early trade routes were maritime. The Comoros archipelago is situated in the western Indian Ocean, midway between the island of Madagascar and the coast of East Africa at the northern end of the Mozambique Channel. The archipelago is composed of four main islands: Grand Comore (Ngazidja
), Anjouan (Ndzuani
), Mohéli (Mwali
) and Mayotte (Maore
). The settlement of the four islands was an integral part of migration within the Indian Ocean, as they represent a potential maritime crossroads and juncture, between Bantu African, Middle Eastern and Southeast Asian (SEA) spheres of influence. The modern Comorian population is the result of a long-term process of biocultural admixture, mainly related to ancient trade and colonisation in the Indian Ocean.
The Comoros and Madagascar share obvious signs of SEA influence including the cultivation of rice (phased out during twentieth century), bananas and coconuts, and the use of outrigger canoes. Evidence from plant translocation suggests a migration from SEA 1500 Years Before Present (YBP).1, 3, 4
Clear genetic evidence for the SEA influence has been found on neighbouring Madagascar.5, 6, 7, 8
On the basis of Y chromosome and mitochondrial variation, ethnic groups with the strongest SEA biocultural features in Madagascar were estimated to have approximately 50% SEA ancestry.5, 8
In contrast to Madagascar where the language, Malagasy, is an Austronesian language with origins in SEA, the languages spoken on the Comoros are of Bantu origin. They are distinct from, but have close affinity to, Swahili, both branching from the precursor Sabaki language, 1000–2000 YBP.9
The cultural contributions of Middle Eastern civilisation are equally evident on the Islands. By 2000 YBP, a thriving commercial maritime network already existed, extending from the Middle East to India, and as far South as Tanzania on the East African coast. The name ‘Comoros' is from the Arabic Kmr, meaning ‘light in the sky'.3
From 1300 YBP, the Comoros archipelago served as a stepping stone, for Middle Eastern traders operating along the East African coast, and for SEA traders travelling to Madagascar and the East African coast.10, 11
By 1000 YBP, the Shirazi, traders with origins in the Persian city of Shiraz in present day Iran, had established themselves on the island of Kilwa. The Shirazi were responsible for the generalisation of Islam on the Swahili coast by 500 YBP. They had built mosques on Kilwa, Zanzibar and Anjouan by 800 YBP.12
Islam remains the religion of the Islands today.
An unambiguous genetic signal from the Middle East has not, however, been detected in East Africa further south than Ethiopia,13, 14
or in the ethnic groups sampled on Madagascar.5, 8
The Lemba people of South Africa, carrying a putative semitic Y chromosome, currently provide the only evidence for gene flow from the Middle East into southern Africa.15
The alleles of some autosomal genes found in the ex-patriot Comorian population living in Marseilles indicate a genetic contribution from Western Eurasia,16, 17, 18
but the populations living on the Comoros have until now not been studied.
In this context, the peopling of the Comoros is evidently integral to the movements of men and women across the entire Indian Ocean. To gain insights into this process, we therefore determined the Y chromosomal and mitochondrial genetic variation on the three Bantu-speaking islands of the Comoros Republic.