New Research by Pusan National University Suggests a Key Role of Ice Age Cycles in Early Human Interbreeding

BUSAN, South Korea, Aug. 15, 2023 /PRNewswire/ -- In a recent study published in Science on 10 August 2023, researchers from Korea and Italy have used genetic data, supercomputer simulations of past climate, and insights obtained from paleoanthropology to answer this question by identifying 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.

Reference

Title of original paper: Climate shifts orchestrated hominin interbreeding events across Eurasia

Journal: Science

DOI:  https://doi.org/10.1126/science.add4459

Corresponding author email: [email protected]; [email protected]

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SOURCE Pusan National University