Nama women of Namibia
The Nama are an indigenous population known to carry exceptional levels of genetic diversity compared to other modern groups.
The Nama are an indigenous population known to carry exceptional levels of genetic diversity compared to other modern groups.
In an article which passed beneath my radar last May, a team of anthropologists led by Professor Brenna Henn of the Genome Center at the University of California, Davis, cast doubt on the theory that modern humans all originated in a single population in East Africa.
Instead, they propose a model in which early Homo sapiens spread across Africa forming partially isolated populations, between which there was limited gene flow by interbreeding.
The earliest split which is still detectable in the DNA of contemporary people occurred between 120,000 to 135,000 years ago after two or more weakly genetically differentiated populations had been mixing for hundreds of thousands of years.
Before creationists start to get over-excited by the news that earlier scientists might have been wrong about the exact details of the evolution of modern humans, they should break the habit of a lifetime and find the courage to read the abstract to the paper in Nature, which makes it clear that the debate is about the details of our evolutionary origins in Africa. There is no serious doubt about the truth of that explanation.
As a UC Davis press release explains:
Although it is widely understood that Homo sapiens originated in Africa, uncertainty surrounds how branches of human evolution diverged and how people migrated across the continent, said Brenna Henn, professor of anthropology and the Genome Center at UC Davis, corresponding author of the research.
Research co-led by Henn and Simon Gravel of McGill University tested a range of competing models of evolution and migration across Africa proposed in the paleoanthropological and genetics literature, incorporating population genome data from southern, eastern and western Africa.This uncertainty is due to limited fossil and ancient genomic data, and to the fact that the fossil record does not always align with expectations from models built using modern DNA. This new research changes the origin of species.
We are presenting something that people had never even tested before. This moves anthropological science significantly forward.
Professor Brenna M. Henn, co-corresponding author
Department of Anthropology
University of California, Davis, CA, USA.
The authors included newly sequenced genomes from 44 modern Nama individuals from southern Africa, an Indigenous population known to carry exceptional levels of genetic diversity compared to other modern groups. Researchers generated genetic data by collecting saliva samples from modern individuals going about their everyday business in their villages between 2012 and 2015.
The model suggests the earliest population split among early humans that is detectable in contemporary populations occurred 120,000 to 135,000 years ago, after two or more weakly genetically differentiated Homo populations had been mixing for hundreds of thousands of years. After the population split, people still migrated between the stem populations, creating a weakly structured stem. This offers a better explanation of genetic variation among individual humans and human groups than do previous models, the authors suggest.
Professor Weaver has expertise in what early human fossils looked like and provided comparative research for the study.Previous more complicated models proposed contributions from archaic hominins, but this model indicates otherwise.
Professor Timothy D. Weaver, co-author
Department of Anthropology
University of California, Davis, CA, USA.
The authors predict that, according to this model, 1-4% of genetic differentiation among contemporary human populations can be attributed to variation in the stem populations. This model may have important consequences for the interpretation of the fossil record. Owing to migration between the branches, these multiple lineages were probably morphologically similar, which means morphologically divergent hominid fossils (such as Homo naledi) are unlikely to represent branches that contributed to the evolution of Homo sapiens, the authors said.
AbstractSo now we have a clearer picture of what our African ancestors were doing in that long period of pre-'Creation Week' history as they whiled away the hours waiting for creationism’s god to create the universe - they were evolving in geographically isolated populations then remixing to give a diverse stem population from which all non-African people are descended.
Despite broad agreement that Homo sapiens originated in Africa, considerable uncertainty surrounds specific models of divergence and migration across the continent1. Progress is hampered by a shortage of fossil and genomic data, as well as variability in previous estimates of divergence times1. Here we seek to discriminate among such models by considering linkage disequilibrium and diversity-based statistics, optimized for rapid, complex demographic inference2. We infer detailed demographic models for populations across Africa, including eastern and western representatives, and newly sequenced whole genomes from 44 Nama (Khoe-San) individuals from southern Africa. We infer a reticulated African population history in which present-day population structure dates back to Marine Isotope Stage 5. The earliest population divergence among contemporary populations occurred 120,000 to 135,000 years ago and was preceded by links between two or more weakly differentiated ancestral Homo populations connected by gene flow over hundreds of thousands of years. Such weakly structured stem models explain patterns of polymorphism that had previously been attributed to contributions from archaic hominins in Africa2,3,4,5,6,7. In contrast to models with archaic introgression, we predict that fossil remains from coexisting ancestral populations should be genetically and morphologically similar, and that only an inferred 1-4% of genetic differentiation among contemporary human populations can be attributed to genetic drift between stem populations. We show that model misspecification explains the variation in previous estimates of divergence times, and argue that studying a range of models is key to making robust inferences about deep history.
Ragsdale, A.P., Weaver, T.D., Atkinson, E.G. et al.
A weakly structured stem for human origins in Africa.
Nature 617, 755-763 (2023). https://doi.org/10.1038/s41586-023-06055-y
© 2023 the authors/Springer Nature Ltd.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.
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