Abstract
Human-mediated biological exchange has had global social and ecological impacts. In sub-Saharan Africa, several domestic and commensal animals were introduced from Asia in the pre-modern period; however, the timing and nature of these introductions remain contentious. One model supports introduction to the eastern African coast after the mid-first millennium CE, while another posits introduction dating back to 3000 BCE. These distinct scenarios have implications for understanding the emergence of long-distance maritime connectivity, and the ecological and economic impacts of introduced species. Resolution of this longstanding debate requires new efforts, given the lack of well-dated fauna from high-precision excavations, and ambiguous osteomorphological identifications. We analysed faunal remains from 22 eastern African sites spanning a wide geographic and chronological range, and applied biomolecular techniques to confirm identifications of two Asian taxa: domestic chicken (Gallus gallus) and black rat (Rattus rattus). Our approach included ancient DNA (aDNA) analysis aided by BLAST-based bioinformatics, Zooarchaeology by Mass Spectrometry (ZooMS) collagen fingerprinting, and direct AMS (accelerator mass spectrometry) radiocarbon dating. Our results support a late, mid-first millennium CE introduction of these species. We discuss the implications of our findings for models of biological exchange, and emphasize the applicability of our approach to tropical areas with poor bone preservation.
Highlights
Human trade, travel, and transport have facilitated the translocation of a vast number of species around the world, creating cosmopolitan assemblages of organisms across all continents [1]
Historical and archaeological sources testify to the long-term engagement of the Swahili coast with the wider Indian Ocean world, through commercial and cultural interactions that promoted the emergence of a cosmopolitan, trade-oriented society by the late first millennium CE [5]
Sites include both cave and open-air types, and coastal, island, and hinterland locations; they date to the Later Stone Age (LSA; up to c. 600 CE), Early Iron Age (EIA; c. 100–600 CE), Middle Iron Age (MIA; c. 600–1000 CE), and/or Later Iron Age (LIA; c. 1000–1650 CE)
Summary
Travel, and transport have facilitated the translocation of a vast number of species around the world, creating cosmopolitan assemblages of organisms across all continents [1]. Earlier exchanges elsewhere in the world have been postulated [3], and here we consider the so-called ‘Monsoon Exchange’ that resulted in the movement of plant and animal species between Asia and Africa [4]. The details of this exchange remain poorly understood, due to a paucity of systematic archaeobotanical, zooarchaeological, and chronometric studies, in Africa. The Swahili coast–a cultural region stretching from southern Somalia to northern Mozambique and including near-shore islands, as well as the Comoros and Madagascar–is a key area for exploring human-mediated biological exchange between Asia and Africa. Biological exchange was part of the Swahili phenomenon, leading to the development, for example, of agricultural systems in which Asian domesticates play a key role [6,7,8]
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