The Green Sahara genomic landscape: insights from whole genome analysis of modern northern African and Sahelian populations

During its last humid phase (12000-5000 years ago), the Sahara was fertile and widely populated, thus allowing coexistence and interactions among various inhabitant groups. The subsequent desertification led to the emergence of the largest geographic barrier of the African continent and to the evolutionary divergence of surrounding territories, North Africa on the northern side and the Sahel belt southward. Despite the extent of this phenomenon, the human population dynamics related to the last Green Sahara are still understudied. In order to characterize at higher resolution the genetic impact of the last Green Sahara and later events, 120 high-coverage (30x) complete modern genomes have been generated from samples across five North African countries and seven Sahelian countries, focusing on ethnic groups among Afro-Asiatic and Nilo-Saharan families, adding 2 Europeans as controls. The samples have been integrated with 43 genomes previously analysed by D’Atanasio et al. 2023, for a total of 163 samples to be compared with relevant modern and ancient datasets from the literature (for a total of 2800), in order to characterize Green Saharan genetic signals and distinguish them from more recent ones. Preliminary analyses reveal a strong structure and heterogeneity among populations on both sides of Sahara, with the presence of isolated groups. For example, the Egyptian Berbers from Siwa Oasis form a cluster far from surrounding groups, showing a greater affinity with Eastern Sahelian populations, while the Tuareg tend to diverge from their Sahelian neighbours towards Eurasian groups. Interestingly, a strong internal genetic structure is observed in Sudan, which seems to link this large territory to both North Africa and the Sahelian belt. This comprehensive dataset, with its broad distribution and diversity, fills a relevant ethno-geographic gap in genomic studies and allows for higher ancestry resolution, through established population genetic approaches, enhancing our understanding of genetic diversity and ancient trans-Saharan dynamics.