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A weakly structured stem for human origins in Africa
Aaron P Ragsdale1, Timothy D Weaver2, Elizabeth G Atkinson3
1Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI, USA.
Nature
|May 17, 2023
Summary
Human origins in Africa involved complex gene flow between ancestral populations, not archaic hominin contributions. This reticulated history dates back to Marine Isotope Stage 5, shaping modern human genetic diversity.
Area of Science:
- Human Evolution
- Population Genetics
- Paleoanthropology
Background:
- Homo sapiens' African origin is accepted, but specific divergence and migration models remain uncertain.
- Limited fossil and genomic data, plus variable divergence time estimates, hinder progress in understanding early human history.
Purpose of the Study:
- To differentiate between various human population divergence and migration models in Africa.
- To infer detailed demographic histories using advanced statistical methods and newly sequenced Khoe-San genomes.
Main Methods:
- Utilized linkage disequilibrium and diversity-based statistics for complex demographic inference.
- Sequenced whole genomes from 44 Nama (Khoe-San) individuals from southern Africa.
- Inferred reticulated population history models for African populations.
Main Results:
- Inferred a reticulated African population history dating back to Marine Isotope Stage 5.
- Earliest divergence among contemporary populations occurred 120,000-135,000 years ago, preceded by gene flow between weakly differentiated ancestral Homo populations.
- Weakly structured stem models explain polymorphism patterns, challenging previous archaic hominin introgression hypotheses.
Conclusions:
- Reticulated population history with early gene flow, rather than archaic introgression, best explains African population structure and genetic diversity.
- Model misspecification accounts for variations in previous divergence time estimates.
- Robust inferences about deep human history require the study of diverse demographic models.
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