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View of the village of Kuboes, on the border of South Africa and Namibia. DNA samples were collected from Nama individuals who have historically lived in the region.
New research confirms what had long been suspected - that early Homo sapiens interbreeding with Neanderthals and Denisovans in Eurasia was not the only place and time that hominins had interbred with other related species.
The research co-led by Professor Brennan Henn, professor of anthropology and the Genome Center at the University of California Davis and Simon Gravel of McGill University, has now shown that early hominins interbreed with other hominins in Africa before spreading to Eurasia and then to the rest of the world, so the world population of H. sapiens does not have a single ancestor but is the result of hybridization and remixing of diverged populations.
As the UC Davis news release explains:
In testing the genetic material of current populations in Africa and comparing against existing fossil evidence of early Homo sapiens populations there, researchers have uncovered a new model of human evolution — overturning previous beliefs that a single African population gave rise to all humans. The new research was published today, May 17, in the journal Nature.The team's findings are published, open access in Nature:
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.
“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,” she said. “This new research changes the origin of species.”
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.
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.Nama woman standing in the doorway to her home in Kuboes, South Africa, a UNESCO World Heritage Site.
Justin Myrick-Tarrant/with permission
“We are presenting something that people had never even tested before,” Henn said of the research. “This moves anthropological science significantly forward.”
“Previous more complicated models proposed contributions from archaic hominins, but this model indicates otherwise,” said co-author Tim Weaver, UC Davis professor of anthropology. He has expertise in what early human fossils looked like and provided comparative research for the study.
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.
Abstract
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 (2023). https://doi.org/10.1038/s41586-023-06055-y
Copyright: © 2023 The authors.
Published by Springer Nature Ltd. Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
Fig. 3: A weakly structured stem best describes two-locus statistics.
It will take a genius and considerable redefinition of everyday words to make this model of human origins over the last 1 million years fit into the creationist/Bible literalist belief that all humans can trace their ancestry back to a single couple created without ancestors just a few thousands years ago, and a genocidal flood with just 8 related survivors about 4000 years ago.
a,b, In the two best-fitting parameterizations of early population structure, continuous migration (a) and multiple mergers (b), models that include ongoing migration between stem populations outperform those in which stem populations are isolated. Most of the recent populations are also connected by continuous, reciprocal migration that is indicated by double-headed arrows (labels matched to migration rates and divergence times in Table 1). These migrations last for the duration of the coexistence of contemporaneous populations with constant migration rates over those intervals. The merger-with-stem-migration model (b, with LL = −101,600) outperformed the continuous-migration model (a, with LL = −115,300). Colours are used to distinguish overlapping branches. The letters a–i represent continuous migration between pairs of populations, as described in Table 1.
No doubt too those who want to believe the Bible tells the truth in some form, so rationalise all the impossible absurdities in it as metaphors or allegories, will be hard pressed to explain how special creation of a couple without ancestors is a metaphor or allegory for what really happened as science is revealing it. Most will probably simple claim it's a metaphor or allegory and leave it at that, invoking mysterious ways, by way of a (non) answer.
Creationists might like to ignore the fact that the researcher, as always, have no doubt at all that the Theory of Evolution provides a complete explanation of the revealed evidence and had no need to invoke supernatural magic by way of an explanation.
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