Genetic history of Chad

Abstract

Objectives: The Sahel is a semi-arid zone stretching from the Atlantic Ocean in the west to the Red Sea in the east and from the Sahara in the north to the Sudanian Savanna in the south. Here, we investigated the genetic history of the spread of Northern African ancestry common among Berbers, the Y DNA haplogroup R1b-V88, and Chadic languages throughout the Sahel, with a focus on Chad. Materials and Methods: We integrated and analyzed genotype data from 751 individuals from Chad, Burkina Faso, Mali, South Sudan, and Sudan in the context of a global reference panel of 5,966 individuals. Results: We found that genetic diversity in Chad was broadly divided by a north-south axis. The core ancestry of Southern Chadians was Central African, most closely related to Pygmies. Southern Chadians then experienced four waves of gene flow over the last 3,000 years from West-Central Africans, Eastern Africans, West-Central Africans again, and then Arabians. In contrast, Northern Chadians did not share Central African ancestry and were not influenced by the first wave of West-Central Africans but were influenced by Northern African ancestry. Discussion: We found that Y DNA haplogroup R1b entered the Chadian gene pool during Baggarization. Baggara Arabs spoke Arabic, not Chadic, implying that people carrying R1b-V88 were not responsible for the spread of Chadic languages, which may have spread approximately 3,700 years ago. We found no evidence for migration of Near Eastern farmers or any ancient episodes involving Eurasian backflow.

High-depth African genomes inform human migration and health

“…2c ). Previous studies on trans-Sahelian migration to west Africa have suggested two distinct waves of migration: one more than 100 generations ago (2,900 years ago) and a more-recent wave in the last 35 generations (1,015 years ago) 24 . On the basis of a variety of east African proxy populations, we estimated that admixture in BRN occurred approximately 50 to 70 generations ago (1,500–2,000 years ago) (Fig.…”

Subsistence strategy was the main factor driving population differentiation in the bidirectional corridor of the African Sahel

“…It has been well established that in the populations of eastern and central Sahel there is a discernible Eurasian genetic component introduced over a long period of time by numerous migration events from different non‐African regions (Galego Llorente et al, ; Haber et al, ; Pickrell et al, ). Successive waves of migration are clearly reflected in both maternal and paternal genetic pools (Bučková et al, ; Černý et al, ; Podgorná et al, ; Shriner & Rotimi, ) and also in autosomal datasets as shown by allele frequency based methods (Triska et al, ; Vicente et al, ).…”

“…In fact, it is present in many other populations, especially in Arabic speakers (Kulichová et al, ). It has been suggested that R1b‐V88 was introduced to this region by Arabic‐speaking pastoralists and represents the genetic signature of the Baggarization process and not the expansion of proto‐Chadic languages (Shriner & Rotimi, ). According to this scenario, R1b‐V88 has been gradually spreading through the Sahel from the 13th century onwards and was introduced into the gene pool of Chadic‐speaking populations (such as the Hausa and Mada) as recently as just 300 years ago (Shriner & Rotimi, ).…”

Sahelian pastoralism from the perspective of variants associated with lactase persistence

“…Low genetic structure of the Sahel/Savannah belt, revealed by uniparental markers, inspired the notion of a bidirectional migration corridor situated between the Sahara and tropical rainforests (Černý et al, 2007; Černý et al, 2009; Černý et al, 2011). Other studies, however, stress the importance of pastoralism as a barrier of gene flow (Bučková, Černý, & Novelletto, 2013; Kleisner et al, 2019; Nováčková et al, 2020; Shriner & Rotimi, 2018). In fact, a high degree of endogamy can be observed among the Fulani pastoralists even today (Hampshire & Smith, 2001), especially in fully nomadic groups such as Wodaade (sing.…”