Résumé
Understanding the origins of major crops and their early diffusion is crucial to reconstructing the history of human societies and their interactions with the environments. In this study, we focused on sorghum, a crop of major worldwide economic and cultural importance. Archaeobotanical evidence suggests that its domestication originated in eastern Sudan during the fourth millennium BCE but its early diffusion remains unclear. We used a genomic approach, combined with archaeobotanical and ethnolinguistic data, to refine the spatial and temporal origin of cultivated sorghum, and to better understand its spread across Africa. We built a probability map of sorghum domestication using genomic data combined with spatial Bayesian modeling. Our findings pinpoint its centre of domestication to a region encompassing Eastern Sudan and Western Ethiopia, which aligns closely with recent archaeobotanical evidence. Our genomic-based model, calibrated on archaeological remains, suggests that the beginning of the expansion of sorghum agriculture took place around 4,600 years ago. Our results suggest that its expansion occurred simultaneously westward and southward from the centre of domestication, at similar speed. Importantly, the structure of sorghum populations mirrors ethnolinguistic groups at different scales, suggesting a co-diffusion of human social groups and sorghum populations. Their association remains even at fine linguistic classification, suggesting that sorghum populations were maintained by complementary processes, such as local adaptation or social barriers to seed exchange. Our study provides an archaeology-independent, genomically-based estimation of sorghum's domestication centre and highlights the intertwined dynamics of biological and social factors in shaping crop diversity. Thus, by integrating interdisciplinary data, the study highlights the advantages of combining biological and social science perspectives to understand crops - and, more broadly, domesticated organisms - as biological, social and historical entities.