Neanderthals and humans interbred in Europe for 5,400 years

Amongst the remains of the Neanderthal inhabitants of a cave in France, researchers have uncovered a hip belonging to a modern human baby. However, after noticing differences between the ancient ilium and that of more recent neonates, the authors of a new study say the infant may represent a previously unknown early lineage of Homo sapiens.



The Grotte du Renne cave is among the most intriguing Paleolithic sites in Europe as it is believed to have been inhabited around the time that modern humans replaced Neanderthals. Within the cave, researchers have uncovered large numbers of stone tools that are representative of the Châtelperronian techno-cultural complex, which arose during this transition period.

Scholars are divided as to which species invented this industry, with some believing Neanderthals came up with it by themselves, others claiming that it was the work of anatomically modern humans (AMH), and others speculating that the two hominids may have worked together. Interestingly, until now, only Neanderthal remains had been found in the Châtelperronian layer within Grotte du Renne, although modern human fossils have been noted in other caves associated with these items.

In light of this ongoing debate, the newly analyzed pelvis may have just thrust the narrative in a new direction. Comparing the specimen to two known infant Neanderthal hip bones and those of 32 recent human deceased neonates, the study authors note that its shape differs significantly from the Neanderthal ilium and is much more in line with AMH morphology.

However, the ancient hip also fell slightly outside the bounds of variation seen in modern human infants, displaying “a more laterally oriented posterior-superior iliac spine.”

“We propose that this is due to its belonging to an early modern human lineage whose morphology differs slightly from present-day humans,” write the study authors. Noting that this lineage has never previously been documented, the researchers say the infant was probably a member of the AMH populations that coexisted with the last Neanderthals during the transition from the Middle to the Upper Paleolithic, 41,000 to 45,000 years ago.

Furthermore, the presence of these ancient modern humans in Grotte du Renne suggests that they may have lived alongside Neanderthals at the time that the Châtelperronian industry emerged. “The makers of the Châtelperronian could then be human groups where Neanderthals and AMH coexisted,” write the researchers.

This, in turn, implies that the development of the Châtelperronian may have “resulted from cultural diffusion or acculturation processes with possible population admixture between the two groups.” In other words, Neanderthals may have upgraded their technologies after observing their modern human neighbors, resulting in a hybrid industry that came to dominate parts of Europe until the last Neanderthals disappeared.

The study is published in the journal Scientific Reports.
www.nature.com/articles/s41598-023-39767-2

The study by researchers at South Korea's Pusan National University, which had been published in Science, found that over the past 400,000 years, breeding between the two extinct subspecies of human was influenced more by the climate than originally thought.

And the fossil of a 90,000-year-old human—found to have a Denisovan father and a Neanderthal mother, according to DNA testing—suggests that sex between the two subspecies was actually quite common.

The Denisovans, or Denisova hominins, are an extinct subspecies of human that lived from 500,000 to 30,000 years ago. Neanderthals, also an extinct subspecies, lived in Eurasia until about 40,000 years ago.

Although the two subspecies favored different habitats most of the time—with Denisovans preferring cooler environments, and Neanderthals preferring the warmth—shifts in the Earth's orbit changed the distribution of vegetation, and the overall environment.

This caused an overlap in the two subspecies migration patterns, increasing the chances of them meeting and breeding.

The Earth's orbit around the sun determines seasonal fluctuations as well as long-term climate. For example, when the Earth is going through a cycle where it is closer to the sun, we experience a warmer climate.

Serbian scientist Milutin Milankovitch believed that periodic changes in the Earth's position relative to the sun determined long-term climate fluctuations, NASA reports. These changes were responsible for Ice Ages—periods of extreme cold driven by a reduction in the planet's temperature.

Scientists already knew that Neanderthal and Denisovans had sex, however they do not know when, where or how often it took place.

To find out more, researchers analyzed paleoanthropological evidence, genetic data and supercomputer simulations of past climate to assess if it had any impact, the study reported. They found that interglacial climates, and the way this shifted vegetation in certain habitats, meant there were more opportunities for the two species to encounter each other.


Recent paleogenomic research revealed that interbreeding was common among early human species. However, little was known about when, where, and how often this hominin interbreeding took place. Using paleoanthropological evidence, genetic data, and supercomputer simulations of past climate, a team of international researchers has found that interglacial climates and corresponding shifts in vegetation created common habitats for Neanderthals and Denisovans, increasing their chances for interbreeding and gene flow in parts of Europe and central Asia.

Contemporary humans carry in their cells a small amount of DNA derived from Neanderthals and Denisovans. "Denny," a 90,000-year-old fossil individual, recently identified as the daughter of a Denisovan father and a Neanderthal mother, bears testimony to the possibility that interbreeding was quite common among early human species. But when, where, and at what frequency did this interbreeding take place?

In a recent study published in Science on 10 August 2023, researchers from Korea and Italy have joined hands to answer this question. Using fossil data, supercomputer simulations of past climate, and insights obtained from genomic evidence, the team was able to identify habitat overlaps and contact hotspots of these early human species. Dr. Jiaoyang Ruan, Postdoctoral Researcher at IBS Center for Climate Physics (ICCP), South Korea, explains, "Little is known about when, where, and how frequently Neanderthals and Denisovans interbred throughout their shared history. As such, we tried to understand the potential for Neanderthal-Denisovan admixture using species distribution models that bring extensive fossil, archeological, and genetic data together with transient Coupled General Circulation Model simulations of global climate and biome."

The researchers found that Neanderthals and Denisovans had different environmental preferences to start with. While Denisovans were much more adapted to colder environments, such as the boreal forests and the tundra region in northeastern Eurasia, their Neanderthal cousins preferred the warmer temperate forests and grasslands in the southwest. However, shifts in the Earth's orbit led to changes in climatic conditions and hence vegetation patterns. This triggered the migration of both these hominin species towards geographically overlapping habitats, thus increasing the chance of their interbreeding.

The researchers further used insights gained from their analysis to determine the contact hotspots between Neanderthals and Denisovans. They identified Central Eurasia, the Caucasus, the Tianshan, and the Changbai mountains as the likely hotspots. Identification of these habitat overlaps also helped the researchers place 'Denny' within the climatic context and even confirmed the other known episodes of genetic interbreeding. The researchers also noted that the Denisovans and Neanderthals would have had a high probability of contact in the Siberian Altai during ~ 340-290, ~240-190 and ~130-80 thousand years ago.

To further elucidate the factors that triggered the 'east-west interbreeding seesaw,' the team examined the change in vegetation patterns over Eurasia over the past 400 thousand years. They observed that elevated atmospheric CO2 concentrations and mild interglacial conditions caused an eastward expansion of the temperate forest into central Eurasia, and the dispersal of Neanderthals into Denisovan lands. On the contrary, lower CO2 concentrations and corresponding harsher glacial climate potentially caused a fragmentation of their habitats, leading to lesser interactions and interbreeding events.

"Pronounced climate-driven zonal shifts in the main overlap region of Denisovans and Neanderthals in central Eurasia, which can be attributed to the response of climate and vegetation to past variations in atmospheric CO2 and northern hemisphere ice-sheet volume, influenced the timing and intensity of potential interbreeding events," remarks senior author Axel Timmermann, Director, ICCP and Professor at Pusan National University, South Korea.

In summary, the study shows that climate-mediated events have played a crucial role in facilitating gene flow among early human species and have left lasting impressions on the genomic ancestry of modern-day humans.
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Materials provided by Pusan National University. Note: Content may be edited for style and length.

Journal Reference:

Jiaoyang Ruan, Axel Timmermann, Pasquale Raia, Kyung-Sook Yun, Elke Zeller, Alessandro Mondanaro, Mirko Di Febbraro, Danielle Lemmon, Silvia Castiglione, Marina Melchionna. Climate shifts orchestrated hominin interbreeding events across Eurasia. Science, 2023; 381 (6658): 699 DOI: 10.1126/science.add4459