Ancient Amalgamations: Significant Research Identifies Time of Human-Neanderthal Genetic Blendings
Research into numerous genomes throughout 50,000 years of human history suggests that contemporary humans and Neanderthals engaged in interbreeding within a limited timeframe, providing insights into the relationships between these ancient groups and distinguishing modern humans from those who departed Africa initially.
A paper recently published in Nature unveiled the oldest modern human genomes, narrowing down the period when Neanderthals and Homo sapiens crossed paths. Another study published in Science shared findings about Neanderthal and human interactions based on genomes from both contemporary and ancient humans.
At least two distinct genetic populations of early modern humans were uncovered in excavation sites in Bulgaria and Czechia. One of these groups, represented by the skull dubbed Zlatý kůň, is one of the earliest modern human populations in Europe. Zlatý kůň’s genome reveals that her population only intermingled with Neanderthals once, while the Bulgarian group might have interacted with their closest human relatives two times.
The team from the Nature study discovered that Zlatý kůň was related to individuals who lived near Ranis, Germany, around 41,000 and 49,500 years ago. The team does not believe that the Ranis population, which had around 3% Neanderthal ancestry, has any descendants in the modern era. Based on genetic analysis, Neanderthal DNA was introduced to the Ranis population around 80 generations prior.
“We know that Ranis and Zlatý kůñ individuals also coexisted with Neanderthals in Europe, but they only possess Neanderthal ancestry that is common among people outside of Africa at present,” stated Arev Sümer, a researcher at the Max Planck Institute for Evolutionary Anthropology and the lead author of the Nature study, during a press conference held earlier this week. “This contrasts with ancient European modern human genomes, such as those from Bulgaria and Romania.”
The Ranis site was initially excavated in the 1930s and revisited for a second round of excavations between 2016 and 2022. “The material that was excavated was predominantly viewed as fauna during that period,” Johannes Krause, a geneticist at the Max Planck Institute for Evolutionary Anthropology, shared during the press conference. By the time excavation in the mid-1930s concluded, World War II had begun. The splintered bone was stored in a museum in central Germany for nearly a century, until a team from the Planck institute revisited the site and discovered bone fragments in a newly dug pit.
Hélène Rougier, a researcher at California State University, Northridge, and co-author of the Science study, analyzed over 100 boxes containing tens of thousands of bone fragments, verifying that the site in Germany housed one of the earliest groups of modern humans in Europe.
“What was truly extraordinary is that it turned out we have the same individual in the old excavation as the new excavation,” Krause commented. “Four of the fragments were actually from the same person, and that person was from the pit and spread out in the old excavation.”
“Why that individual ended up scattered over several square meters–we can only speculate about what happened there 45,000 years ago,” Krause added. “Not even wanting to think about what might have caused such a scattering of a human.”
A significant discovery in the Nature study: The remains of early modern humans older than 50,000 years outside Africa correspond to entirely distinct non-African populations without any modern-day descendants. In other words, the remains of an approximately 50,000-year-old early modern human found outside Africa would not be an ancestor of modern humans.
All humans possess a small percentage of Neanderthal DNA. Although Neanderthals no longer walk the Earth as a distinct species, our closest human relatives were closely related enough to interbreed and slowly hybridize. In some areas of East Asia, the proportion of Neanderthal DNA in human genomes is approximately 24% higher than in other regions. Even traits related to the shape of tall noses can be traced back to our closest human relatives.
The Science study investigated over 300 genomes from the last 50,000 years of human evolution. 59 genomes belonged to ancient individuals who lived between 2,200 and 45,000 years ago. The research revealed that humans inherited Neanderthal genes associated with skin color, immune responses, and metabolism.
The team aimed to understand the timing and duration of Neanderthal admixture and found that Neanderthal gene flow took place during an interbreeding event between 43,500 and 50,500 years ago. Krause reported that the effective early modern human population size was around 5,000 individuals, and Neanderthals mixed into that population over a somewhat rapid time period–possibly several centuries.
"The significance of this timing is crucial as it impacts the timeline of the Out of Africa migration," noted Priya Moorjani, a molecular biologist at UC Berkeley and the paper's senior author, during the press conference. "Our findings suggest that the Out-of-Africa migration concluded by 43,500 years ago, and earlier migrations might have stemmed from individuals who didn't contribute to today's non-African population."
The relatively recent intermingling of Neanderthals and humans reminds us of Thorin, a 45,000-year-old Neanderthal fossil found in France, whose genetics were investigated recently. Thorin's remains showed his genetic uniqueness from other local groups for approximately 50,000 years.
The state of affairs in Eurasia around 39,500 years ago was further complicated by the Campanian Ignimbrite eruption, which spewed ash from Italy to Russia. As per Krause, "This disaster led to the extinction of early human groups, alongside Neanderthals, and the emergence of the first Europeans who share our genetic lineage was marked by their burial in the ash. So, post-volcano." Krause added, "It's quite an intriguing coincidence, but it could be an explanation. However, it remains a theory for now."
Neanderthals vanished from the fossil record around 39,000 years ago – shortly following the interbreeding activities suggested in the Science and Nature papers. This ancient human group was absorbed by our own and continues to exist (in a way) through their genetic legacy.
"In essence, they weren't two separate species, but two groups," Moorjani explained. "The significant variations we thought separating these groups were comparatively minor genetically. We were strikingly similar, rather than different."
The discovery of Neanderthal DNA in modern human genomes suggests a future of exploring the genetic similarities and differences between our species and our closest human relatives. advances in science and technology will likely reveal even more insights into our shared history with Neanderthals.
The findings from the Nature and Science studies challenge the traditional view of human evolution, suggesting that Neanderthals and modern humans interbred more recently than previously believed. This new understanding of our past could shape future theories about human evolution and enhance our understanding of human genetics.
