Abstract
The fate of hunting and gathering populations following the rise of agriculture and pastoralism remains a topic of debate in the study of human prehistory. Studies of ancient and modern genomes have found that autochthonous groups were largely replaced by expanding farmer populations with varying levels of gene flow, a characterization that is influenced by the almost universal focus on the European Neolithic.1-5 We sought to understand the demographic impact of an ongoing cultural transition to farming in Southwest Ethiopia, one of the last regions in Africa to experience such shifts.6 Importantly, Southwest Ethiopia is home to several of the world's remaining hunter-gatherer groups, including the Chabu people, who are currently transitioning away from their traditional mode of subsistence.7 We generated genome-wide data from the Chabu and four neighboring populations, the Majang, Shekkacho, Bench, and Sheko, to characterize their genetic ancestry and estimate their effective population sizes over the last 60 generations. We show that the Chabu are a distinct population closely related to ancient people who occupied Southwest Ethiopia >4,500 years ago. Furthermore, the Chabu are undergoing a severe population bottleneck, which began approximately 1,400 years ago. By analyzing eleven Eastern African populations, we find evidence for divergent demographic trajectories among hunter-gatherer-descendant groups. Our results illustrate that although foragers respond to encroaching agriculture and pastoralism with multiple strategies, including cultural adoption of agropastoralism, gene flow, and economic specialization, they often face population decline.
Highlights
In order to test hypotheses pertaining to the impact of foragingto-farming transitions, we estimated genetic ancestry, relative genetic isolation, and the timing and magnitude of demographic fluctuations in Eastern African populations
Our investigation focuses on the Chabu, a group of transitioning hunter-gatherers (HGs) who inhabit the Southwestern Ethiopian highland forests that straddle the borders between the Oromia Regional State, Gambella Regional State, and the Southern Nations, Nationalities, and Peoples’ Region (SNNPR).[7]
We include genomic data from Bayira, a 4,500-year-old individual found in Mota Cave in the nearby Gamo Highlands who lived well before any evidence of agriculture or pastoralism in the region,[12,13] as well as additional ancient genomes from Eastern Africa, the Levant, and Anatolia
Summary
We aimed to sample 50 individuals per population per field season
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