Tautalus
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The paper proposes a new explanation for how Neandertals originated that differs from the traditional view that they evolved mainly from earlier Eurasian populations. The author argues that Neandertals may instead have formed through a major geographic expansion of a population closely related to modern humans between about 400,000 and 250,000 years ago. As this expanding population spread into Eurasia, it encountered and interbred extensively with local archaic human groups that were already living there.
Because the local archaic populations were large and well established, most of their genetic material was incorporated into the expanding population through repeated mixing. Over time this process produced a population that looked genetically very similar to the local archaic humans overall, but that still carried some genetic lineages originating from the incoming modern-related population. This model helps explain a puzzling genetic pattern seen in ancient DNA: Neandertals share certain key genetic elements with modern humans, such as mitochondrial DNA and Y-chromosome lineages, even though most of their genome appears more closely related to Denisovans and other archaic groups.
The paper uses population genetic simulations to show that when a small expanding population mixes with a large resident population, extensive introgression can cause the expanding population to become genetically dominated by local ancestry while still preserving some of its original lineages. According to the author, this process could naturally produce the genetic patterns observed in Neandertals. The hypothesis is also consistent with archaeological evidence, particularly the spread of Levallois stone-tool technology around the same time period, which appears in both Neandertal and early modern human contexts and may reflect cultural transmission associated with population movements.
In conclusion, the author suggests that Neandertals may best be understood as the result of a demographic expansion of modern-human–related populations followed by large-scale interbreeding with archaic Eurasians. This scenario provides a single framework that can explain the unusual combination of genetic similarities and differences between Neandertals, modern humans, and Denisovans, and it highlights the importance of population expansions and gene flow in shaping human evolutionary history.
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.
