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.
Brenna Henn/UC Davis.
Research first published in Nature in 2023 shows just how wide of the mark the Bronze Age authors of the Bible’s origin myths were when they guessed at human origins. Of course, in the absence of any knowledge or understanding of the true age of Earth, the history of life on it, or the existence of deep human ancestry, their guesses were no better than we would expect from people trying to explain the world with folklore rather than evidence.
In fact, as the evidence in the 2023 paper by a team co-led by Professor Brenna Henn of the University of California, Davis, and Simon Gravel of McGill University, Montreal, Quebec, Canada, shows, modern humans did not emerge from a single founding couple, or even from one simple, isolated ancestral population. Instead, our origins lie in a complex, dynamic network of human groups that diversified within Africa, evolved in partial isolation, and later exchanged genes as populations moved and merged.
In that respect, human evolution resembles other cases in nature where populations diverge, remain partly distinct, and yet continue to exchange genes — such as the carrion crow/hooded crow Corvus complex, the Eurasian complex of the great tit (Parus major) and its related forms, and the circumpolar herring gull/lesser black-backed gull Larus complex. These examples show evolution not as a neat ladder or a set of separately created “kinds”, but as a branching, reticulating process in which boundaries can be blurred by gene flow.
This process of diversification and later remixing continued in Eurasia, where Homo sapiens interbred with Neanderthals, Denisovans and, possibly, other human populations. Neanderthals eventually disappeared as a distinct population, or were partly absorbed into expanding Homo sapiens populations, around 40,000 years ago.
Far from the single ancestral couple that may have seemed intuitive to parochial Bronze Age pastoralists, modern humanity emerged from a population history that looks less like a single line of descent and more like a tangled bush with cross-linking branches.
The researchers reached this conclusion by analysing DNA sequenced from saliva samples from 44 modern Nama individuals from southern Africa, an Indigenous population known to carry exceptionally high levels of genetic diversity compared with many other modern groups. From that genetic data, the team developed a model suggesting that the earliest detectable split among ancestral human populations occurred between 120,000 and 135,000 years ago, after two or more weakly differentiated Homo populations had already been interbreeding for hundreds of thousands of years.
Even after that split, migration continued between the populations, producing what the researchers describe as a “weakly structured stem” for modern human origins in Africa. Rather than a single stem from which humanity simply sprouted, human evolution is better understood as a reticulated process: branching, merging, and branching again.
How DNA is used to model human origins. DNA does not give scientists a simple family tree with every ancestor named. What it provides is a record of inherited variation: small differences in the genetic code that have accumulated through mutation, recombination, isolation, migration, population growth, and interbreeding. Population geneticists use those patterns to test which historical model best explains the genetic diversity seen in living people.The team’s research, and its significance for understanding modern human origins, was explained in a UC Davis College of Biological Sciences news item by Karen Nikos-Rose:
In the 2023 Nature paper, the researchers compared genome data from African populations, including newly sequenced genomes from 44 Nama individuals from southern Africa, a population noted for exceptionally high genetic diversity. They then tested competing models of African human origins and migration to see which one best matched the observed genetic patterns.
The basic principle is that populations which share a recent common history tend to share more genetic variants. Populations that have been partly isolated for longer tend to accumulate different frequencies of variants. But if those populations later exchange genes, the resulting pattern is not a clean split, but a reticulated one — a network of branching and reconnection. That is why modern DNA can reveal not merely descent, but also past population structure, migration and admixture.
Researchers look at several kinds of evidence in the genome. These include overall genetic diversity, the frequency of particular variants, how variants are shared between populations, and linkage disequilibrium — the tendency for genetic variants close together on a chromosome to be inherited together. The Nature study specifically used diversity-based statistics and linkage disequilibrium to compare alternative demographic models of human origins.
The process is rather like testing different historical scenarios against the evidence. One model might assume that all modern humans descended from a single, isolated ancestral population. Another might assume several partially separated populations that continued to exchange genes. Computer simulations can then ask: if this model were true, what patterns of genetic variation should we expect to see today? The model whose predictions most closely match the real genetic data is treated as the better explanation — not as absolute proof, but as the best-supported reconstruction from the available evidence.
In this case, the best-fitting model was not a simple “single origin population” model. It suggested that the earliest detectable split among ancestral populations contributing to living humans occurred about 120,000–135,000 years ago, but only after two or more weakly differentiated Homo populations had already been exchanging genes for hundreds of thousands of years. Even after that split, migration continued between the stem populations.
This is why the researchers describe modern human origins as having a “weakly structured stem”. The ancestral populations were not separate species in the familiar sense, nor were they isolated branches with no contact. They were more like regional populations within a wider African human metapopulation, periodically exchanging genes as climate, geography and population movement brought them into and out of contact.
This also explains why DNA evidence can sometimes complicate the fossil evidence. Fossils preserve anatomy, but DNA preserves patterns of ancestry. If several ancient populations were genetically connected by migration, their fossils might look broadly similar even if their descendants contributed unevenly to later populations. The UC Davis summary notes that this model may affect how fossils are interpreted, because multiple interacting lineages could have been morphologically similar.
The important point is that DNA-based models are not guesses in the creationist sense. They are statistical tests of competing explanations. They begin with observable genetic data, make predictions from different historical scenarios, and reject models that fail to fit the evidence. In this case, the evidence points not to a single ancestral couple, nor even to a neat single ancestral population, but to a long, complex, African history of divergence, partial isolation, migration and genetic remixing.
New UC Davis Research Using DNA Changes Origin of Human Species
New model for human evolution suggests Homo sapiens arose from multiple closely related populations
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 [2023], in the journal 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. This new research changes the origin of species.
Professor Brenna M. Henn, co-senior author.
Department of Anthropology
University of California
Davis, CA, USA.
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.
Nama woman standing in the doorway to her home in Kuboes, South Africa, a UNESCO World Heritage Site.Justin Myrick-Tarrant.
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.
We are presenting something that people had never even tested before. This moves anthropological science significantly forward.
Professor Brenna M. Henn.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.
[Professor Weaver] 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.
Additional co-authors include Aaron Ragsdale, University of Wisconsin, Madison; Elizabeth Atkinson, Baylor College of Medicine; and Eileen Hoal and Marlo Möller, Stellenbosch University, South Africa.
Publication:
Of course, none of this could have been known to the authors of Genesis, who were not recording history but composing origin folklore from within the narrow intellectual world available to them. They knew nothing of DNA, population genetics, deep time, extinct human relatives, African population structure, or the long, complex evolutionary processes that produced modern humans. Their story of a single created couple was not a revelation of hidden knowledge; it was exactly the sort of simple tale people would invent in the absence of evidence.
Science, by contrast, does not begin with a conclusion and then force the facts to fit it. It begins with evidence — fossils, genomes, archaeology, comparative anatomy and statistical modelling — and allows the picture to become more complicated when the facts demand it. In this case, the evidence does not point to a single ancestral pair in a magic garden, nor to humanity appearing fully formed a few thousand years ago. It points to hundreds of thousands of years of population divergence, migration, interbreeding and remixing within Africa, followed by further interbreeding with other human populations in Eurasia.
That is the difference between mythology and science. The Bible gives us a simple story because simple stories are what pre-scientific people used to explain what they could not investigate. Science gives us a more complex story because reality is more complex — and because modern methods can now recover details of human ancestry that were utterly beyond the imagination of Bronze Age pastoralists.
And, as always, the creationist response is not to improve their model, because they do not have one. It is to deny, ignore or misrepresent the evidence. But the DNA remains where it is, in our cells, carrying the record of a deep, branching and interwoven ancestry that no literal reading of Genesis can accommodate without first abandoning almost everything the evidence shows.
Humanity was not founded by a single couple in a mythological garden. We are the living descendants of an ancient African network of populations — divided, reunited and reshuffled by evolution over immense spans of time.
Advertisement
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
Amazon
All titles available in paperback, hardcover, ebook for Kindle and audio format.
Prices correct at time of publication. for current prices.
No comments :
Post a Comment
Obscene, threatening or obnoxious messages, preaching, abuse and spam will be removed, as will anything by known Internet trolls and stalkers, by known sock-puppet accounts and anything not connected with the post,
A claim made without evidence can be dismissed without evidence. Remember: your opinion is not an established fact unless corroborated.