A very interesting suggestion was prepublished on March 13 in Biorxiv by David Reich, 2026, it is work in progress, and a model, but its title tells it all: Hypothesis: A modern human range expansion ~300,000 years ago explains Neandertal origins.
Trying to explain why the split date between the human lineage and Neanderthals differs when you consider nuclear DNA (765-550 kya) or mtDNA (365-400 kya), or why the original Y chromosome of Neanderthals appears to have vanished, and what we have found is so similar to ours, and that their mtDNA is remarkably similar to ours, Reich suggests that they are a population that arose from modern humans introgression with archaics in Europe. This also explains some incongruent dates and other oddities found in the Atapuerca Sima de los Huesos remains. Simple hypothesis that is very similar to the proposal maed by Cosimo Posth published in Nature, which I commented in a post back in 2017 (An even older Out of Africa event (270kya)!!). Posth suggested that African inflow was "responsible for providing the mtDNA to the Late Pleistocene Neanderthals might have been an even earlier Middle Pleistocene gene flow from Africa, occurring in a time interval that we date between 413 and 268 ka... The temporal corridor for this introgression event between 460 ka and 219 ka is compatible with the evidence of archaeological similarities between Africa and western Eurasia during the Lower to Middle Paleolithic transition39 and potentially may explain the dissimilarities in Middle Paleolithic industries between eastern and western Eurasia. Environmental changes across this time span might have facilitated a hominin expansion out of Africa and potentially spread cultural innovations such as the Levallois technology into Eurasia." Reich developed the concept. Below is the Abstract of Reich's paper
"Abstract.
This paper demonstrates the feasibility of the hypothesis that Neandertals formed when a population using recently developed Levallois stone tool technology expanded between 400-250 thousand years ago (ka). In Europe, their range expansion into an area with Sima de los Huesos-like people led to massive introgression of local archaic genes producing a population with around 95% archaic ancestry (Neandertals); if this range expansion was sex-biased it would provide a simple explanation for why Neandertals retain modern human lineage Y chromosomes or mitochondrial DNA. In Africa, interbreeding with local archaic humans led to more modest archaic admixture and the deep substructure detected in all modern humans today. This proposal explains four previously perplexing similarities of modern humans and Neandertals—sharing of mitochondrial DNA, Y chromosomes, Levallois tools, and 300-200 ka date of formation by mixture—even while Neandertals and Denisovans cluster genome-wide."
This is the paper: Hypothesis: A modern human range expansion ~300,000 years ago explains Neandertal origins David Reich. bioRxiv 2026.03.11.711219; doi: https://doi.org/10.64898/2026.03.11.711219.
This paper is interesting because it also mentions humans mixing with archaics inside of Africa, a source of diversity:
"... ancestors of all modern humans including sub-Saharan Africans were deeply substructured, due to the coming together a few hundred thousand years ago of lineages that began diverging a million or more years ago. For example, ref. 16 models modern human ancestry as largely derived from a mixture of about 80% from a lineage that was most closely related to Neandertals and Denisovans, and 20% from a lineage that diverged from it around 1.5 million years ago, with the two coming together around 300 ka. The remixture is estimated to date to around the same time as the genetically inferred interbreeding of modern humans and archaic humans in the ancestors of Neandertals 300-200 ka. This raises the possibility that these mixtures in Europe and Africa had related causes: a range expansion of a successful population interbreeding with local archaic groups. In Europe, there was massive introgression of local genes because barriers to producing viable offspring were few. In Africa, the mixture was with a more divergent archaic lineage, result in a lower γ (cross-group interbreeding rate), and less introgression..."
This is the reference "ref. 16" cited above: Cousins T, Scally A, Durbin R, (2025) A structured coalescent model reveals deep ancestral structure shared by all modern humans. Nat Genet 57, 856–864.
Comments
I am surprised at the different conclusions that the same datasets of human genes and fossils produce (some are mutually exclusive): humans and Neanderthals are the same, humans and Neanderths split after the Denisovans split, Denisovans and humans split after the Neanderthal split, dates that range from 500 to over 1 million years, introgressions all over (Denisovan to Neanderthal to Human, Human to Neanderthal, Denisovan to Human, one or more lineages of superarchaics introgressing into different hominins). Surely they can't all be right.
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