Researchers from the National University of Busan in South Korea and the University of Naples in Italy explored how rising atmospheric carbon dioxide and the associated warming of global climates may have encouraged the interbreeding of early human species. The findings, which appear in a leading science journal, shed new light on how ancient humans like Homo sapiens, Neanderthals, and Denisovans may have shared habitats and genetic material during periods of environmental change.
Modern humans carry traces in their DNA from earlier relatives. In the genomes of people alive today, segments inherited from Neanderthals and Denisovans can still be detected. In 2018, researchers announced the discovery of an ancient individual who lived roughly 90,000 years ago and was nicknamed Denny. The genome suggested his mother belonged to Neanderthals and his father to Denisovans, illustrating a history of interbreeding among distant cousins.
In the latest study, scientists drew on a wealth of ancient genetic data and ran climate models for the distant past using high-performance computing. The analysis revealed distinct climate preferences for the two groups: Denisovans were better suited to cold environments such as tundra landscapes, while Neanderthals favored temperate forests and grasslands. This divergence in habitat preferences helped explain the historical geographic separation of the two populations, with Neanderthals tending to occupy the southwest of Eurasia and Denisovans the northeast.
As climates warmed and carbon dioxide levels rose, glacier retreat and shifting ecosystems allowed the two groups to encroach on overlapping zones. Those periods of overlap increased opportunities for encounters and, consequently, the likelihood of interbreeding events between Neanderthals, Denisovans, and early Homo sapiens. The study’s results align with known episodes of hybridization that occurred around 120,000, 78,000, and 90,000 years ago, confirming a recurring pattern during the late Pleistocene across different regions.
The researchers went further by mapping potential Denisovan habitats beyond their previously understood ranges. Their work suggests that northern Europe, portions of Russia, and areas in China might have provided suitable environments for Denisovans, broadening the geographic picture of where these ancient people could have lived. While the presence of Denisovans west of the Altai Mountains remains uncertain, genetic analyses of contemporary European populations offer a path to resolving this question.
Additional climate data and more fossil evidence are expected to illuminate how interbreeding events unfolded between roughly 210,000 and 320,000 years ago. By integrating genetic signals with climate reconstructions, researchers can better understand how ancient populations responded to shifting landscapes, altered food sources, and changing temperatures. This multidisciplinary approach helps clarify the complex history of human evolution and the ways in which climate has shaped genetic legacies across continents.
As the study points out, the question of which continents bear the greatest impact from climate change remains multifaceted. Insights from ancient climate-human interactions offer useful context for interpreting contemporary changes, underscoring the long, intertwined history of environmental shifts and human adaptation across regions around the world.