A new paper in PNAS reports on the use of “genome-wide genetic data to show that there are at least two admixture events in the history of Khoisan populations (southern African hunter–gatherers and pastoralists who speak non-Bantu languages with click consonants)”. The authors suggest that the first admixture event took place about 3,000 years ago (1500 generations ago) into eastern Africa and this was followed by a migration into Southern Africa about 900 – 1,800 years ago.
There is some archaeological and linguistic support for the earliest admixture event around 3,000 years ago as being from the biblical Kingdom Of Sheba (presumed to be in current day Saudi Arabia) into Northern Ethiopia. The “architecture in the Ethiopian culture of D’mt has an “unmistakable South Arabian appearance in many details“. It is also believed that Ethio-semitic languages were introduced into Ethiopia from Saudi Arabia around the same time. A close connection between Sheba and D’mt (Damot) is entirely plausible across the short stretch of water separating them.
Joseph K. Pickrella, et al, Ancient west Eurasian ancestry in southern and eastern Africa, doi: 10.1073/pnas.1313787111
Abstract: The history of southern Africa involved interactions between indigenous hunter–gatherers and a range of populations that moved into the region. Here we use genome-wide genetic data to show that there are at least two admixture events in the history of Khoisan populations (southern African hunter–gatherers and pastoralists who speak non-Bantu languages with click consonants). One involved populations related to Niger–Congo-speaking African populations, and the other introduced ancestry most closely related to west Eurasian (European or Middle Eastern) populations. We date this latter admixture event to ∼900–1,800 y ago and show that it had the largest demographic impact in Khoisan populations that speak Khoe–Kwadi languages. A similar signal of west Eurasian ancestry is present throughout eastern Africa. In particular, we also find evidence for two admixture events in the history of Kenyan, Tanzanian, and Ethiopian populations, the earlier of which involved populations related to west Eurasians and which we date to ∼2,700–3,300 y ago. We reconstruct the allele frequencies of the putative west Eurasian population in eastern Africa and show that this population is a good proxy for the west Eurasian ancestry in southern Africa. The most parsimonious explanation for these findings is that west Eurasian ancestry entered southern Africa indirectly through eastern Africa.
The authors write in their discussion
The most striking inference from this analysis is the presence of west Eurasian ancestry in southern Africa that we date to 900–1,800 y ago. Several lines of evidence suggest that the population that brought this ancestry to southern Africa was an already-admixed population from eastern Africa.
Back-to-Africa Gene Flow in Eastern Africa. A major open question concerns the initial source of the west Eurasian ancestry in eastern Africa. The estimated mean time of gene flow in eastern Africa is around 3,000 y ago, and the amount of gene flow must have been quite extensive, because the west Eurasian ancestry proportions reach 40–50% in some Ethiopian populations. Archaeological records from this region are sparse, so Pagani et al. (10) speculate that this admixture is related to the Biblical account of the Kingdom of Sheba. However, archaeological evidence is not completely absent. During this time period, architecture in the Ethiopian culture of D’mt has an “unmistakable South Arabian appearance in many details”, although there is some debate as to whether these patterns can be attributed to large movements of people versus elite-driven cultural practices. Additionally, linguistic evidence suggests that this time period was when Ethiosemitic languages were introduced to Africa, presumably from southern Arabia. It is perhaps not a coincidence that the highest levels of west Eurasian ancestry in eastern Africa are found in the Amhara and Tygray, who speak Ethiosemitic languages and live in what was previously the territory of D’mt and the later kingdom of Aksum.
Based on these analyses, we can propose a model for the spread of west Eurasian ancestry in southern and eastern Africa as follows. First, a large-scale movement of people from west Eurasia into Ethiopia around 3,000 y ago (perhaps from southern Arabia and associated with the D’mt kingdom and the arrival of Ethiosemitic languages) resulted in the dispersal of west Eurasian ancestry throughout eastern Africa. This was then followed by a migration of an admixed population (perhaps pastoralists related to speakers of Khoe–Kwadi languages) from eastern Africa to southern Africa, with admixture occurring ∼1,500 y ago.