Ancient west Eurasian ancestry in southern and eastern Africa (1307.8014v2)

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 approximately 900-1,800 years 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 approximately 2,700 - 3,300 years 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 paper reveals that genome-wide data analysis identifies at least two admixture events introducing west Eurasian ancestry, with evidence dating from 900 to 3,300 years ago.
• The paper employs LD-based techniques and ALDER software to establish genetic timelines and quantify ancestry impacts on diverse African populations.
• The paper suggests that west Eurasian ancestry infiltrated Africa indirectly through eastern migrations, reshaping historical genetic narratives and aligning with archaeological evidence.

Insights into Ancient West Eurasian Ancestry in Southern and Eastern Africa

The paper presented in this paper investigates the complex genetic history of southern and eastern Africa, focusing on the integration of west Eurasian ancestry within these regions. Employing genome-wide data, it dissects the admixture events impacting Khoisan populations and correlates these findings with the historical population dynamics of eastern Africa. This synthesis not only reveals insights into past migrations but also highlights methodological advancements in extracting historical genetic information from modern populations.

Genetic Evidence for Admixture Events

The research identifies at least two significant admixture events involving Khoisan populations. One event is marked by interactions with African groups speaking Niger-Congo languages. More notably, the other admixture introduces west Eurasian ancestry, linked to populations currently inhabiting areas around Europe or the Middle East. Estimations date this event to 900-1,800 years ago, with the most substantial demographic impact evident among Khoisan groups speaking Khoe-Kwadi languages. This west Eurasian genetic signal is not limited to southern Africa; similar traces were found in eastern African populations from Kenya, Tanzania, and Ethiopia, with a much earlier introduction, dated approximately 2,700-3,300 years ago.

Analytical Approaches and Findings

Utilizing linkage disequilibrium (LD)-based techniques, the authors employ a robust methodology to evaluate genetic admixture across the populations studied. They implement the ALDER software to re-evaluate historical admixture in populations like Ju$|$'hoan_North and establish portions of west Eurasian ancestry. The weighted LD curves, computed with various reference populations, illuminate the depth of admixture and contribute to temporal estimates of these genetic influxes. This analysis reveals that, in several Khoisan populations, the inputs from non-Khoisan sources are multifaceted, with west Eurasian ancestry infiltrating earlier rather than in recent historical times.

Implications of West Eurasian Ancestry

The paper proposes a significant hypothesis regarding west Eurasian ancestry within the African continent—these ancestries in southern Africa likely trace indirect pathways through eastern Africa. The corroboration of admixture events, both in timing and genetic signatures, across these regions suggests west Eurasian ancestry in southern Africa may have diversified initially in eastern Africa before dispersal further southward.

This research contributes to the understanding of historical movements, potentially linking them with migrations from the Levant or Arabian peninsula into eastern Africa. It provides a cohesive genetic narrative aligning with archaeological and linguistic evidence of trans-regional interactions and migrations over the past few millennia.

Theoretical and Future Considerations

The findings contribute significant insights into the historical gene flow dynamics across Africa, challenging earlier perceptions that modern populations' genetic structures were predominantly shaped in situ. This reveals a more intricate historical landscape influenced by substantial transcontinental connections. Such interpretations are reinforced by correlating genomic data with archaeological and linguistic evidence, offering a more nuanced approach to understanding human history and migration patterns.

Future work could focus on expanding genomic data from localized archaeological finds, allowing verification of proposed models through ancient DNA analysis. Moreover, as genotyping technology progresses, a broader sampling across Africa could refine our understanding of genetic influences and migrations, offering clarity into human evolutionary history.

This research, by elucidating the genetics of past demographic events within African populations, lays a robust foundation for further exploration into the continent’s complex human history and genetic makeup.