進化：最古の現生人類ゲノムから、4万5,000年前にネアンデルタールとの混血があったことが判明

Analysis of the oldest-known genomes from early modern humans in Europe, who lived around 45,000 years ago, helps to provide a more precise date for when Neanderthals and modern humans mixed. The research, published in Nature, suggests that mixing occurred in a single event between 45,000 and 49,000 years ago, which is more recent than previous estimates. The findings provide insights into the demographics of early modern humans and the earliest Out-of-Africa migrations.

Modern humans arrived in Europe more than 45,000 years ago and overlapped for at least 5,000 years with Neanderthals. At least two genetically distinct groups of early modern humans inhabited Europe; these groups are represented by individuals from Bacho Kiro, Bulgaria and a woman named Zlatý kůň, from Czechia. Zlatý kůň is part of the earliest population to diverge from the Out-of-Africa lineage and suggests only one mixing event with Neanderthals; however, the ancestry of the ancient individuals from Bacho Kiro suggests two mixing events. Recent research has identified the presence of early modern humans in central and southern Europe around 41,000–49,500 years ago, following radiocarbon-dating of bone fragments from Ilsenhöhle in Ranis, Germany. However, how these individuals relate to other groups present in Europe at the time is unclear.

Arev Sümer and colleagues analysed one high-coverage genome, and five low-coverage genomes isolated from the Ranis bone fragments, estimated to be around 45,000 years old. They also analysed a high-coverage genome from Zlatý kůň and found a fifth- or sixth-degree genetic relationship with two Ranis individuals. These results suggest that these individuals are part of the same group that represents the earliest known split from the Out-of-Africa lineage. The authors also found there was close kinship within the six Ranis individuals, identifying a mother–daughter pair, and suggest that this group was part of a small population that left no descendants among present-day people.

The Ranis individuals were shown to have around 2.9% Neanderthal ancestry, which Sümer and colleagues posit originates from a single mixing event common among all non-African individuals. The authors date this event to approximately 45,000–49,000 years ago (around 80 generations before the Ranis individuals lived). This finding implies that the ancestors of all currently sequenced non-Africans lived in a common population at this time and that individuals from more than 50,000 years ago outside Africa represent different non-African populations. The results might also help to date the mixing with other extinct ancient hominins such as the Denisovans.

Sümer and colleagues conclude that more research is needed to explore the events following the Out-of-Africa migration and the earliest movements of modern humans across Europe and Asia.