Recent paleogenomic research has revealed that interbreeding was common in early human species. However, little was known about when, where, and how often this hominin interbreeding occurred. Scientists have found that Neanderthals and Denisovans had different environmental preferences.
Using paleoanthropological evidence, genetic data, and supercomputer simulations of past climates, an international team of researchers found that interglacial climates and corresponding shifts in vegetation created common habitats for Neanderthals and Denisovans, increasing their chances of interbreeding and gene flow in parts of Europe and Central Asia.
Modern humans carry small amounts of DNA derived from Neanderthals and Denisovans in their cells. “Denny,” a 90,000-year-old fossil recently identified as the daughter of a Denisovan father and a Neanderthal mother, provides evidence that interbreeding was common in early human species. But when, where, and at what frequency did this crossover occur?
Using fossil data, supercomputer simulations of past climates, and insights gleaned from genomic evidence, the team was able to identify habitat overlaps and contact points for these early human species. Dr. Jiaoyang Ruan, a postdoctoral researcher at the IBS Center for Climate Physics (ICCP), South Korea, explains: “Little is known about when, where and how often Neanderthals and Denisovans interbred during their shared history.
As such, we sought to understand the potential for Neanderthal-Denisian admixture using species distribution models that bring extensive fossil, archaeological, and genetic data together with transient global climate and biome simulations with the Coupled General Circulation Model.”
Scientists have found that Neanderthals and Denisovans had different environmental preferences from the start. While the Denisovans were much more adapted to cooler environments such as the boreal forests and tundra region of northeastern Eurasia, their Neanderthal cousins ​​preferred the warmer temperate forests and grasslands of the southwest.
Shifts in the Earth’s orbit, however, led to changes in climatic conditions and thus vegetation patterns. This triggered the migration of both of these hominin species into geographically overlapping habitats, increasing the chance of their interbreeding.
The researchers further used the insights gained from their analysis to determine contact hotspots between Neanderthals and Denisovans. They identified central Eurasia, the Caucasus, Tianshan, and the Changbai Mountains as likely outbreaks. Identifying these habitat overlaps also helped researchers place “Denny” in a climatic context and even confirmed other known episodes of genetic interbreeding. The researchers also noted that Denisovans and Neanderthals had a high probability of contact in the Siberian Altai ~340-290, ~240-190 and ~130-80 thousand years ago.
To further elucidate the factors that triggered the “East-West Crossing Swing”, the team examined the change in vegetation patterns in Eurasia over the past 400,000 years. They observed that increased atmospheric CO2 concentrations and mild interglacial conditions caused the eastward expansion of the temperate forest into central Eurasia and the dispersal of Neanderthals into the Denisovan lands. Conversely, lower CO2 concentrations and a corresponding harsher glacial climate potentially fragmented their habitats, resulting in less interaction and interbreeding.
Significant climate-driven zonal shifts in the major Denisovan–Neanderthal overlap region of central Eurasia, which can be attributed to the response of climate and vegetation to past changes in atmospheric CO2 and Northern Hemisphere ice sheet volume, affected the timing and intensity. of potential crossover events.
The study shows that climate-mediated events played a key role in facilitating gene flow between early human species and left lasting impressions on the genomic ancestors of modern humans.
Reference: https://www.sciencedaily.com/releases/to2023/08/230814122355.htm
