An international team of scientists have examined the ancient history of atmospheric CO2 on Earth and unraveled its effects on the evolution of the species Homo sapiens.
Early human species included Neanderthals, Denisovans and Homo sapiens, with interbreeding among the species likely to be a common occurrence during the era of early hominins. This is evidenced by the presence of Neanderthal DNA in modern humans, as well as the recent discovery of an individual with a Denisovan father and Neanderthal mother who lived 90,000 years ago.
In a new study published in Science, researchers used paleo-anthropological evidence and genetic data, combined with computer models of past climate conditions, to track where and how Neanderthals and Denisovans preferred to live. They discovered that Denisovans were suited to cold environments, while Neanderthals were more adapted to the milder climates of temperate forests and grassland.
“This means that their habitats of choice were separated geographically, with Neanderthals typically preferring southwestern Eurasia and Denisovans the northeast," says study lead author Dr. Jiaoyang Ruan.
However, conditions occasionally brought the two species together. Warm interglacial periods and elevated levels of CO2 encouraged temperate forests to expand eastward into central Eurasia. This effectively created corridors leading Neanderthals into Denisovan habitat. "It is as if glacial-interglacial shifts in climate created the stage for a unique and long-lasting human love story, whose genetic traces are still visible today," says Dr. Ruan.
This study comes on the heels of another Science article which recently identified a massive cooling event 1.1 million years ago that disrupted early human occupation of Europe. Analyzing deep ocean sediment cores with the help of a new supercomputer climate model, researchers found a cooling event to the scale of 7℃. They then input their findings into a human habitat model and discovered that the environmental conditions were unsuitable for early Homo erectus, implying that early humans must have vacated Europe during this period. Their hypothesis correlates with a lack of stone tools and human remains in the area during a 200,000 year period surrounding the cold period, with repopulation of Europe occurring approximately 900,000 years ago.
"Our study on past climates documents the sensitivity of Southern European vegetation and human food resources to North Atlantic temperature changes,” says study author Prof. Timmermann. “This result adds to the mounting evidence that our human history has been shaped by past climate changes.”
Sources: Cell; Nature; Science, 2023a; ScienceDaily, 2023a; Science, 2023b; ScienceDaily, 2023b