Modelling ancient patterns
In ecology, species distribution models predict where a species could live based on where it has been observed. Burke and her team applied this logic to ancient hominids, using archaeological sites—rather than observation data from living animals—as “presence points” for Neanderthals and Homo sapiens.
The study involved a series of modelling steps. First, Burke created four habitat suitability models for both species, using tools from conservation biology and geomatics. These models incorporated archaeological data along with a suite of geographical and climate variability indices.
Burke then compared the results of the four models, creating new models that identified “core” regions—geographic areas large and productive enough to support stable populations and, crucially, connected to one another.
“Obviously, we don’t have precise demographic data for populations living 35,000 years ago, so we used ethnographic data from better-documented ancient hunter-gatherer groups to set parameters for the geomatics tools and generate these models,” Burke explained. “For example, these data show that the typical annual territory of a local group of 25 to 50 individuals, moving seasonally and maintaining regional connections with other groups, would be about 2,500 km².”
Resilience through connectivity
It was at this point in the analysis that differences between Neanderthals and Homo sapiens started to emerge.
For example, regions favourable to Homo sapiens were found to be more highly connected than those of Neanderthals. According to Burke, connectivity is crucial because interconnected populations form networks, allowing members to move to allied, related or partner groups in response to climatic, ecological or demographic shocks.
“These networks act as a safety net,” explained Burke. “They allow for the exchange of information on resources and animal migrations, the forming of partnerships, and temporary access to other territories in the event of a crisis.”
Burke was quick to point out that this does not mean Neanderthal groups were incapable of sustaining connections between groups. Archaeological data on the flow of material objects and other evidence indicate that they too developed interregional networks. However, according to the models, the regional connections within the Neanderthal network were relatively tenuous, particularly in Central and Eastern Europe.
Mix of factors
The study also showed that climate variability, or how rapidly and unpredictably conditions change, affected populations more than did absolute temperature or precipitation.
“Climate variability appears to have played a major role. So it turns out that humans have been sensitive to environmental variability throughout our history,” said Burke.
However, climate alone cannot explain why the Neanderthals went extinct, since fossil and archaeological evidence shows they survived earlier glacial cycles.
According to Burke, the Neanderthals disappeared due to a complex mix of interacting factors, including climate instability, demographic pressures and social organization. It is also possible that the exact combination of factors that drove their extinction differed between regions.
For example, the study shows that the Neanderthal population in Europe was divided into two groups, one in the west and another in the east.
In Eastern Europe, limited connectivity may have isolated Neanderthal populations as climatic conditions deteriorated. In contrast, on the Iberian Peninsula, at the western edge of their range, better-connected core regions may have enabled populations to persist longer.
But the story may not be so straightforward.
“In western areas, the arrival of Homo sapiens may have added further stress, especially for Neanderthal populations that were already demographically vulnerable,” said Burke. “Because the two species were capable of producing offspring together, their interactions were likely complex, involving competition, occasional interbreeding and other subtle population dynamics.”
Fundamental human need
Burke believes that these ancient dynamics invite reflection on some of humankind’s enduring challenges.
“Human migration has always existed, facilitated by mobility and social networks,” she noted. “Even today, despite the complexities of borders, population densities and social inequalities, humans continue to migrate for the same fundamental reasons: to find more favourable areas, reunite with loved ones and join mutual aid networks.”
It’s a timely reminder that, today as 40,000 years ago, our survival depends not only on technology and intelligence, but also on our ability to forge and maintain connections.
