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New Insights Into Human-Neanderthal Interbreeding

Genetic ancestry tests often reveal surprising results, such as the presence of Neanderthal DNA in individuals of non-African descent. Research indicates that these individuals contain approximately 1 to 4 percent of their genomes inherited from this extinct relative. This points to a significant historical interaction between ancient modern humans (Homo sapiens) and Neanderthals. Recent studies published in Science and Nature have clarified the timeline of this interbreeding more precisely than ever before.

According to Priya Moorjani, a biologist at UC Berkeley and co-senior author of the Science study, the timing of these interactions carries significant implications for our understanding of human migration out of Africa. Moorjani highlights that this research adds depth to the historical context of how ancient humans settled in regions beyond Africa, often inferred through archaeological finds and fossils.

The lineage of Neanderthals and modern humans traces back to a common ancestor that emerged in Africa. As some of these ancestors migrated, they evolved into Neanderthals approximately 500,000 years ago, while most modern humans remained in Africa until around 100,000 years ago. This later group eventually encountered Neanderthals as they spread into Europe and Asia.

Both recent studies independently suggest that interbreeding between Neanderthals and modern humans occurred during a notable period of contact roughly 47,000 years ago. The Science study indicates that this blending began around 50,500 years ago and persisted for approximately 7,000 years, corroborating archaeological records that suggest prolonged coexistence between these two species.

As Fernando Villanea, an anthropologist from the University of Colorado Boulder, explains, the findings indicate a scenario wherein humans frequently encountered Neanderthals, leading to a sustained period of interbreeding rather than isolated incidents.

The research team from the Science study evaluated 275 contemporary human genomes alongside 58 ancient genomes from Europe and Central Asia, revealing a singular extended timeline of gene flow. Meanwhile, the Nature research involved sequencing ancient genomes from a 45,000-year-old family group, which showed signs that Neanderthal DNA entered their lineage approximately 80 generations prior. However, this specific population is now extinct, as their genetic contribution is absent in modern genomes.

The identification of Neanderthal DNA in contemporary non-African populations raises questions regarding the timing of human dispersal. This suggests modern humans may have migrated to areas like East Asia and Oceania following the noted interbreeding, a claim that is at odds with archaeological evidence indicating human presence in regions such as China 100,000 years ago and Australia 65,000 years ago. Pontus Skoglund, a paleogeneticist at the Francis Crick Institute, posits that either the dating of these archaeological findings may need reassessment, or ancient lineages that reached these areas ultimately did not contribute to modern genetic diversity.

Moreover, the genetic inheritance from Neanderthals has had varying effects on Homo sapiens, with some Neanderthal gene segments presumably linked to adverse health effects while others may have conferred benefits, especially to early modern humans adapting to new environments.

Alexander Platt, a geneticist at the University of Pennsylvania, described the simultaneous identification of this interbreeding period by both studies as “striking” and of considerable importance for understanding human history.

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