The historical spread of Arabian Pastoralists to the eastern African Sahel evidenced by the lactase persistence −13,915*G allele and mitochondrial DNA

Abstract

Even if the age of the most recent common ancestor of -13,915*G is ∼4 ka as shown in a previous study, our results suggest that its spread to Africa was more recent, which is consistent with the migrations of Arabic tribes. Because the incidence of sub-Saharan mtDNA haplotypes is negatively correlated with the occurrence of -13,915*G, we suggest that the decrease of its frequency in Africa has been caused by progressive admixture of the Arabian nomads with sub-Saharan populations.

Genetic history of the African Sahelian populations

“…In fact, Arabic populations in Africa, that still maintain a nomadic way of life and keep camels (the Abbala), also have a higher frequency of the −13915*G variant and fewer L-type mtDNA haplogroups (predominantly observed in sub-Saharan Africa) than African Arabs keeping cattle (the Baggara). 87 On another hand, the Fulani pastoralists living in the western part of the Sahel/Savannah belt bear the same LP variant (−13910*T) as Eurasian populations 88,89 (Figure 2), which might be due to a common ancestral LP haplotype with Europeans. 90 It could be suggested that a higher consumption of fat contained in milk (and/or meat) of domesticated animals by these peoples shaped also the variation of genes involved in lipid metabolism, but thus far signals of selection at such genes have only been detected in populations living in the eastern part of the Sahel/Savannah belt.…”

“…The frequency of this allele displays a partially clinal pattern implying that it spread from Arabia to Africa very recently. In fact, Arabic populations in Africa, that still maintain a nomadic way of life and keep camels (the Abbala), also have a higher frequency of the − 13915*G variant and fewer L‐type mtDNA haplogroups (predominantly observed in sub‐Saharan Africa) than African Arabs keeping cattle (the Baggara) …”

“…New DNA samplings of Arabian nomads in Sudan and Chad generated larger data sets of haplotypes linked to LP. To gain a deeper insight on the spread of Arabian‐speaking nomads in the eastern Sahel/Savannah belt, joint estimates of ages and growth rates for the − 13915*G allele based on the diversity of surrounding SNPs have been computed for several populations . In this latter study, the distribution of mtDNA haplogroups associated with LP in sub‐Saharan and Eurasian populations has also been analysed.…”

“…In this latter study, the distribution of mtDNA haplogroups associated with LP in sub‐Saharan and Eurasian populations has also been analysed. It has been shown that the expansion of the − 13915*G variant is chronologically associated with the historically documented expansion of Bedouin camel herders into sub‐Saharan Africa, and that the adoption of cattle by some groups such as the Baggara went hand in hand with their substantial admixture with sub‐Saharan populations …”

“…84 Arabic pastoralists living in the eastern parts of the Sahel/Savannah belt share the same LP variant (−13915*G) as the peoples of the Arabian Peninsula (Figure 2), a finding believed to be due to a common ancestry. [85][86][87] The frequency of this allele displays a partially clinal pattern implying that it spread from Arabia to Africa very recently. In fact, Arabic populations in Africa, that still maintain a nomadic way of life and keep camels (the Abbala), also have a higher frequency of the −13915*G variant and fewer L-type mtDNA haplogroups (predominantly observed in sub-Saharan Africa) than African Arabs keeping cattle (the Baggara).…”