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Baby, it’s cold outside. New research suggests early human species interbred during ice ages.

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Contemporary humans have a small amount of DNA derived from Neanderthals and Denisovans in their cells. A recent study published in Science on August 10, 2023, reveals that early human species interbred. The study was conducted by researchers from Korea and Italy, who used fossil data, supercomputer simulations of past climate, and genomic evidence to identify habitat overlaps and contact hotspots of these 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 discovered that Neanderthals and Denisovans had different preferences for environments. Denisovans were better suited to colder environments, like the boreal forests and tundra region in northeastern Eurasia, while their Neanderthal relatives preferred warmer environments like temperate forests and grasslands in the southwest. However, changes in the Earth’s orbit caused shifts in climate and vegetation patterns, which led both hominin species to move to overlapping habitats, increasing the chance of their interbreeding.

Using their analysis, the researchers located the contact hotspots between Neanderthals and Denisovans. They found that Central Eurasia, the Caucasus, the Tianshan, and the Changbai mountains were likely hotspots. Identifying these overlaps also helped place ‘Denny’ in the climatic context and confirmed other known episodes of genetic interbreeding. The researchers also noted that the Denisovans and Neanderthals likely had contact in the Siberian Altai around 340-290, 240-190, and 130-80 thousand years ago.

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