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real expert
05-09-22, 07:45
Phylogeography of Sub-Saharan Mitochondrial Lineages Outside Africa Highlights the Roles of the Holocene Climate Changes and the Atlantic Slave Trade :


Despite the importance of ancient DNA for understanding human prehistoric dispersals, poor survival means that data remain sparse for many areas in the tropics, including in Africa. In such instances, analysis of contemporary genomes remains invaluable. One promising approach is founder analysis, which identifies and dates migration events in non-recombining systems. However, it has yet to be fully exploited as its application remains controversial. Here, we test the approach by evaluating the age of sub-Saharan mitogenome lineages sampled outside Africa. The analysis confirms that such lineages in the Americas date to recent centuries—the time of the Atlantic slave trade—thereby validating the approach. By contrast, in North Africa, Southwestern Asia and Europe, roughly half of the dispersal signal dates to the early Holocene, during the “greening” of the Sahara. We elaborate these results by showing that the main source regions for the two main dispersal episodes are distinct. For the recent dispersal, the major source was West Africa, but with two exceptions: South America, where the fraction from Southern Africa was greater, and Southwest Asia, where Eastern Africa was the primary source. These observations show the potential of founder analysis as both a supplement and complement to ancient DNA studies.


we performed a second analysis, stipulating a model with two migration events. The first is at 8 ka, corresponding to the Holocene Climate Maximum, accounting for the 7.4–10.0 ka peaks in the founder analyses into North Africa (A), Southwest Asia (B), Europe (C) and Iberia (D), and the second is at 0.5 ka, corresponding roughly to the start of the Atlantic slave trade
The results for North Africa suggested that about half of the sub-Saharan lineages arrived in the early Holocene, and the other half in recent times. However, when analysing the putative source location of the lineages in each migration event, the distribution differed. Amongst the prehistoric arrivals, half of the North African mtDNA founders were from West Africa, with much of the other half associated with Eastern Africa. However, there were substantially more lineages from West Africa, and correspondingly fewer from Eastern Africa, when considering the origin of lineages in recent times....

For Europe, our founder analyses suggest that there are more African mtDNA lineages related to the prehistoric than the historical period (~60:40). Note, however, that most of the lineages here considered in the European analysis are from Iberia , as displayed in Figure 3 for both prehistoric (Figure 3A) and historical arrivals (Figure 3B). Typically, North African lineages are well represented in the prehistoric period (a third of the total). However, the higher percentage of sub-Saharan lineages arriving in Europe during this period, mostly from West Africa (63%) is likely from migrants that first crossed the Sahel belt into North Africa and moved from there into Europe via the Strait of Gibraltar. Although not detected in modern North Africa’s maternal genetic background (which is very heterogeneous: [49]), these results suggest that most early Holocene migrations from Africa into Europe occurred via the West Mediterranean.