Unraveling the Genetic Tapestry: When Neanderthals and Early Humans Engaged in a Genetic Dance

While some may be astonished to discover Neanderthal DNA in their ancestry results, individuals of non-African heritage derive 1 to 4 percent of their genomes from this extinct human relative. This indicates that ancient modern humans (Homo sapiens) mated with Neanderthals at some point. Recently, two distinct studies published in the journals Science and Nature in December have pinpointed this interbreeding phase more accurately than before.

“The timing is crucial, as it directly affects our comprehension of the timeline regarding the out-of-Africa migration,” Priya Moorjani, a biologist from the University of California, Berkeley, and co-senior author of the Science paper, remarks in a statement. “It also influences our understanding of the settlement in regions outside Africa, typically inferred from archaeological findings or fossils in various locations worldwide.”

Neanderthals and modern humans originated from a joint African ancestor. Some of these ancestors ventured out of Africa into Eurasia, evolving into Neanderthals approximately 500,000 years ago. Most of our lineage remained in Africa until about 100,000 years ago when some Homo sapiens began migrating out of the continent—and encountered Neanderthals in Europe and Asia.

The recent investigations came to similar conclusions independently: that the interbreeding responsible for the existence of Neanderthal DNA in our genomes today transpired during a continuous interaction around 47,000 years ago. The Science study suggests that mixing began approximately 50,500 years ago and persisted for roughly 7,000 years. This estimate aligns with archaeological evidence indicating an inter-species coexistence lasting between 6,000 and 7,000 years, according to the statement.

“It tells a different narrative than just a rare encounter. Whenever you met a Neanderthal, it was acceptable to have a child with a Neanderthal,” Fernando Villanea, an anthropologist at the University of Colorado Boulder who was not part of either study, explains to the Washington Post’s Carolyn Y. Johnson. “It constructs a narrative that is logical in terms of real-world processes. For an extended duration, humans were encountering Neanderthals, and they were having offspring.”

The team behind the Science research examined 275 contemporary human genomes along with 58 ancient modern human genomes from remains in Europe and Western and Central Asia. They compiled a genetic database and utilized it to identify the moments when Neanderthal DNA integrated into our ancestors’ genomes, discovering a “single, shared extended period of gene flow,” as stated in the paper.

On the other hand, the researchers from the Nature study sequenced the oldest known modern human genomes, belonging to seven individuals from a 45,000-year-old family associated with the LRJ culture. They found that Neanderthal DNA had entered the family tree 80 generations prior—a timeframe for interbreeding that aligns with the findings of the Science paper. However, even though this group had Neanderthal ancestry, their population must have become extinct, as their DNA does not currently contribute to modern genomes.

If individuals of non-African descent possess Neanderthal DNA from the interbreeding event recognized by both studies, it may imply that Homo sapiens spread to areas such as East Asia and Oceania only afterward. However, this notion contradicts the archaeological evidence of modern humans in China dating back 100,000 years and 65,000-year-old findings from Australia. Pontus Skoglund, a paleogeneticist at the Francis Crick Institute who did not participate in the studies, conveys to the New York Times’s Carl Zimmer that either the archaeological sites were inaccurately dated, or the modern human lineages that arrived in those areas 100,000 years ago eventually became extinct and thus did not contribute to our current genetic makeup.

“The history of humanity is not merely a tale of triumph. We faced extinction multiple times,” Johannes Krause, a biochemist at the Max Planck Institute for Evolutionary Anthropology and a co-author of the Nature paper, shares with NBC News’ Evan Bush. “There are numerous lineages we have now identified that did not contribute to subsequent populations.”

The Neanderthal genes passed down to Homo sapiens influenced the health of our forebears. Certain sections of the modern human genome lacking Neanderthal genes, for instance, indicate that specific components of their DNA could have been lethal to Homo sapiens, leading to the extinction of individuals with those genes, according to the statement. Conversely, the researchers also discovered high-frequency Neanderthal genes that likely benefitted the early Homo sapiens, who were relative newcomers in that region.

Alexander Platt, a geneticist at the University of Pennsylvania who did not engage with either research paper, mentions to Nature News’s Freda Kreier that the finding that both studies pinpointed a singular interbreeding phase is “notable” and “revelatory.”