Humans have been living on all but one of Earth’s continents for thousands of years, but how Homo sapiens spread across the planet remains a mystery.
Most models suggest that early humans relied on warmer climatic conditions to migrate north, but a new survey of archaeological materials suggests that humans were enduring frigid conditions – similar to those found in modern-day northern Scandinavia – much earlier than previously thought.
According to the new research, published Wednesday in the journal Science Advances, early human populations were surprisingly adaptable and resilient.
“Using these new insights, new models of the spread of our species across Eurasia will now need to be constructed, taking into account their higher degree of climatic flexibility,” study co-author Jean-Jacques Hublin, director of the Department of Human Evolution at the Max Planck Institute, said in a press release.
For the study, scientists focused on human habitation inside Bacho Kiro Cave, an important archaeological site in Bulgaria.
Researchers analyzed archaeological materials dating back thousands of years, including the remains of herbivores butchered by human occupants.
From these materials, scientists extracted paleoclimate data, which allowed researcher to produce a detailed record of what local climate conditions were like at the times when humans were occupying the cave.
The technique offers a better idea of the context of local climates, as opposed to more common correlations made between archaeological data and climatic archives from different locations, said study co-author Kate Britton.
“It really gives us insight into what life was like ‘on the ground,'” said Britton, who is also a researcher at Max Planck Institute for Evolutionary Anthropology and the University of Aberdeen
Few archaeological sites can offer both evidence of human habitation and reliable paleoclimate data, making it difficult to do the kinds of analysis conducted since Bacho Kiro Cave.
“Due to the time consuming nature of the analysis and the reliance on the availability of particular animal remains, oxygen isotope studies or other ways of generating climatic data directly from archaeological sites remain scarce for the time period when Homo sapiens first spread across Eurasia,” said lead study author Sarah Pederzani, who is also a researcher at the Max Planck and Aberdeen.
Pederzani spent a year drilling into the teeth of ancient animals recovered from the cave. Using stable isotope ratio mass spectrometry, researchers were able to precisely date the animals remains, as well as collect details about the local climate conditions.
“Through this time intensive analysis that included a total of 179 samples, it was possible to obtain a very highly resolved record of past temperatures, including summer, winter and mean annual temperature estimates for human occupations spanning more than 7,000 years,” said Pederzani.
The latest analysis followed a multiyear effort to recover archaeological materials from Bacho Kiro Cave. Deposits from the cave’s lowest portion yielded a variety of animal bones, stone tools, pendants and even human remains.
The artifacts suggest humans had begun spreading into southeastern Europe from the Levant as early as 45,000 years ago — tolerating subarctic conditions as they moved into the region.