How Neanderthals and Denisovans interbred due to early climate change
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In 2018, scientists concluded that Neanderthals and the reclusive Denisovans mated and produced children. This was established from the fossilized bones of a teenager who lived 90,000 years ago and had a Denisovan father and a Neanderthal mother.
Even though the two split genetically some 400,000 to 500,000 years ago, this established that interbreeding was common among hominins. And now, a new study is laying the groundwork for how climate conditions might have played a role in where and how early human species interbred.
The study found that there were climate-driven zonal shifts in central Eurasia, which was at the time occupied by both Denisovans and Neanderthals. The changes in atmospheric CO2, which led to changes in vegetation and shifts in climate, determined the interbreeding practices between the two species.
The team of scientists combined fossil, archaeological, and genetic data with model simulations of global climate and biomes. They found that Neanderthals and Denisovans had different environmental preferences, according to a press release published in Eurekalert.
The researchers studied and analyzed the age and location of 22 Denisovan artifacts and 773 Neanderthal remains. Combining these with genetic data and supercomputer simulations of the ancient climate, the researchers could map out the distribution patterns of the two hominid lineages over time, reported IFL Science.
“Compared to Neanderthals, Denisovans were present in hot and humid climates, which points to a comparatively wider niche space,” wrote the researchers in the study. “Whereas Neanderthals were more abundant in temperate forests, Denisovans were present in both boreal forest and tundra.”
“This means that their habitats of choice were separated geographically, with Neanderthals typically preferring southwestern Eurasia and Denisovans the northeast”, said Dr. Jiaoyang Ruan, lead author of the study.
Looking at their habitat overlap, Ruan et al. found interbreeding patterns that correlated with climate and environmental change in Eurasia. In a study published earlier this month, contrary to the notion that humans have never gone extinct, researchers found that extreme climate change in Europe may have temporarily wiped out early hominins from the continent.
The study was published in the journal Science.
Study abstract:
When, where, and how often hominin interbreeding happened is largely unknown. We study the potential for Neanderthal-Denisovan admixture using species distribution models that integrate extensive fossil, archaeological, and genetic data with transient coupled general circulation model simulations of global climate and biomes. Our Pleistocene hindcast of past hominins’ habitat suitability reveals pronounced climate-driven zonal shifts in the main overlap region of Denisovans and Neanderthals in central Eurasia. These shifts, which influenced the timing and intensity of potential interbreeding events, can be attributed to the response of climate and vegetation to past variations in atmospheric carbon dioxide and Northern Hemisphere ice-sheet volume. Therefore, glacial-interglacial climate swings likely played an important role in favoring gene flow between archaic humans.
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