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This paradigm-shifting research, published in the prestigious journal PLOS One, suggests that both Neanderthals and later Mesolithic hunter-gatherers significantly altered vegetation patterns across the European continent. This finding compels us to re-evaluate the deep history of human-environment interactions and consider the notion that anthropogenic landscapes are not a recent phenomenon but have roots stretching back tens of thousands of years into the Paleolithic era. The study provides compelling evidence that the human imprint on Europe’s ecosystems is far older and more extensive than previously understood, effectively pushing back the timeline for significant human influence on the planet.
Computer Models Unlock Secrets of Early Human Impact
The international team behind this pivotal research was led in part by researchers at Aarhus University in Denmark. Their methodology represents a sophisticated fusion of cutting-edge computational power and meticulous paleoenvironmental reconstruction. They utilized advanced computer simulations, a powerful tool for reconstructing complex past scenarios, to examine how a confluence of factors – including climate fluctuations, the presence and activities of large animals (megafauna), the occurrence of natural fires, and crucially, the actions of early human populations – collectively shaped European vegetation during two distinct warm periods in prehistory.
The true innovation of their approach lay in the subsequent step: comparing these intricate simulations with extensive and highly detailed fossil pollen data meticulously collected from the same eras across the continent. Fossil pollen, preserved in lake sediments and peat bogs, acts as a microscopic time capsule, offering invaluable insights into the types of plants that dominated ancient landscapes. By painstakingly matching the outcomes of their predictive models with this real-world botanical evidence, preserved for millennia in geological strata, the researchers were able to quantify and estimate the relative influence of each factor on the ancient plant cover. This rigorous validation process, pitting theoretical models against empirical data, lends immense credibility to their conclusions.
"The study paints a new picture of the past," explains Jens-Christian Svenning, a professor of biology at Aarhus University and a lead author on the study. He underscores the interdisciplinary nature of the project, which brought together a diverse consortium of experts from various fields, including archaeology, geology, and ecology, spanning institutions across The Netherlands, Denmark, France, and the UK. This collaborative spirit was essential for tackling such a multifaceted research question.
Professor Svenning elaborates on a key moment in their analytical process: "It became clear to us that climate change, large herbivores and natural fires alone could not explain the pollen data results. Factoring humans into the equation – and the effects of human-induced fires and hunting – resulted in a much better match." This realization was a critical turning point, indicating that human activities were not merely minor perturbations but rather essential variables required to accurately model the ancient European landscape.
Humans and the Decline of Megafauna: A Shifting Landscape
The researchers focused their investigations on two specific, ecologically significant warm intervals in European history, each characterized by different human inhabitants and environmental contexts.
The first period examined was the Last Interglacial, a warm phase occurring approximately 125,000 to 116,000 years ago. During this epoch, Neanderthals (Homo neanderthalensis) were the sole human species inhabiting Europe. This was a time of remarkable biodiversity, with Europe supporting a wide array of megafauna. Straight-tusked elephants (Palaeoloxodon antiquus), towering beasts that could reach over four meters in height and weigh up to 13 tonnes, roamed alongside rhinoceroses, European bison (Bison priscus), aurochs (Bos primigenius), wild horses, and various species of deer. These massive herbivores played crucial ecological roles, shaping vegetation through grazing and browsing, creating pathways, and disturbing soil.
The second period of focus was the Early Holocene, spanning approximately 12,000 to 8,000 years ago. This era immediately followed the Last Glacial Maximum (the peak of the most recent Ice Age) and witnessed a significant global warming trend and the re-establishment of temperate forests. During this time, Mesolithic hunter-gatherers from our own species, Homo sapiens, had spread across the region, having replaced Neanderthals.
A stark difference emerged when comparing the megafauna of these two periods. By the Mesolithic, the vibrant tapestry of megafauna that characterized the Last Interglacial had significantly altered. Many of the largest animals, such as the straight-tusked elephant and Merck’s rhinoceros, had vanished entirely, while the numbers of other large species had sharply declined. This shift reflects a broader, global pattern of megafauna losses that closely followed the global dispersal of Homo sapiens, a phenomenon often attributed, at least in part, to human hunting pressure – the so-called "overkill hypothesis." The study thus provides regional evidence that aligns with this larger narrative of human impact on global biodiversity.
A New View of Prehistoric Europe: Active Co-Creators
The quantitative results of the simulations are compelling. "Our simulations show that Mesolithic hunter-gatherers could have influenced up to 47% of the distribution of plant types," states Anastasia Nikulina, one of the lead researchers. This astonishing figure suggests a profound and widespread impact, indicating that nearly half of the observed vegetation patterns during the Early Holocene could be attributed to human activities. The Neanderthal effect, while smaller, was still measurable and significant, demonstrating their capacity to alter landscapes: "approximately 6% for plant type distribution and 14% for vegetation openness," Nikulina adds.
Human influence manifested in two primary, yet interconnected, ways. One direct mechanism was the deliberate or accidental use of fire. Early humans utilized fire for various purposes: clearing undergrowth to facilitate travel, driving game during hunts, creating open areas to encourage the growth of specific plants, or even for signaling. Such fires, whether natural or human-ignited, burned trees and shrubs, preventing forest regeneration in certain areas and promoting the expansion of grasslands or early successional plant communities.
The other crucial mechanism, often overlooked in previous studies, was the indirect effect of hunting large herbivores. This is a prime example of a trophic cascade, where the removal or reduction of one species has ripple effects throughout an ecosystem. "The Neanderthals did not hold back from hunting and killing even giant elephants," Professor Svenning emphasizes, highlighting the remarkable skill and coordination required for such feats. "And here we’re talking about animals weighing up to 13 tonnes." The implications of hunting these behemoths were far-reaching. Fewer grazing animals meant a reduction in the natural disturbance they inflicted on vegetation. Without the constant browsing and trampling pressure from large herbivores, areas that would otherwise have remained open or savanna-like would have experienced increased "overgrowth," leading to denser, more closed vegetation.
However, Svenning notes a crucial distinction between Neanderthal and Homo sapiens impact: "the effect [of Neanderthal hunting] was limited, because the Neanderthals were so few that they did not eliminate the large animals or their ecological role – unlike Homo sapiens in later times." This suggests a difference in scale and intensity of impact, possibly due to population densities, hunting technologies, or societal organization. Mesolithic Homo sapiens, with their likely larger populations, more sophisticated toolkits (e.g., microliths for composite weapons), and perhaps more systematic landscape management strategies, appear to have exerted a far greater and more pervasive influence.
According to Nikulina and Svenning, these findings fundamentally challenge the long-held idea that Europe was an untouched, pristine wilderness before the advent of agriculture around 8,000 years ago. This traditional view often casts prehistoric hunter-gatherers as living "in harmony" with nature, having minimal impact. This study strongly refutes that notion.
"The Neanderthals and the Mesolithic hunter-gatherers were active co-creators of Europe’s ecosystems," asserts Jens-Christian Svenning. This perspective reframes early humans not as passive inhabitants, but as integral, dynamic components of the ecological systems they occupied. Anastasia Nikulina elaborates, stating, "The study is consistent with both ethnographic studies of contemporary hunter-gatherers and archaeological finds, but goes a step further by documenting how extensive human influence may have been tens of thousands of years ago – that is, before humans started farming the land." This consistency with modern observations of hunter-gatherer societies, known for their sophisticated ecological knowledge and landscape management practices, further strengthens the study’s conclusions.
AI Simulations and Interdisciplinary Research: A New Frontier
Nikulina emphasizes the inherently interdisciplinary nature of the project, which seamlessly integrated multiple fields, including ecology (understanding species interactions and ecosystem dynamics), archaeology (providing evidence of human presence, tools, and activities), and palynology (the study of pollen for reconstructing past vegetation). This holistic approach was critical for building a comprehensive understanding of the complex interactions at play.
A significant technological leap for the team involved the development of highly detailed computer models specifically designed to simulate ancient ecosystems. "This is the first simulation to quantify how Neanderthals and Mesolithic hunter-gatherers may have shaped European landscapes," Nikulina highlights. She further explains the dual strengths of their innovative approach: "it brings together an unusually large set of new spatial data spanning the whole continent over thousands of years, and it couples the simulation with an optimization algorithm from AI. That let us run a large number of scenarios and identify the most possible outcomes." The use of artificial intelligence, likely through machine learning algorithms or Bayesian inference, allowed the researchers to process vast amounts of data, explore a multitude of environmental scenarios, and statistically determine the most probable drivers of vegetation change, thus increasing the robustness and reliability of their findings.
Professor Svenning reinforces the undeniable clarity provided by the modeling process: "The computer modeling made it clear to us that climate change, the large herbivores such as elephants, bison and deer, and natural wildfires alone cannot explain the changes seen in ancient pollen data." This reiterates the core message: to truly comprehend the vegetation patterns of prehistoric Europe, human impacts – both direct (like fire use) and indirect (like hunting-induced trophic cascades) – must be taken into account. He adds a particularly insightful point: "Even without fire, hunter-gatherers changed the landscape simply because their hunting of large animals made the vegetation denser." This highlights the often-underestimated power of indirect human influence on ecosystems.
While this study represents a monumental leap in our understanding, the researchers acknowledge that gaps remain in our knowledge about the nuanced ways early humans influenced their environments. The findings open up exciting avenues for future exploration.
Nikulina and Svenning suggest that similar sophisticated simulations could be applied to other regions and time periods globally. North and South America, as well as Australia, present particularly intriguing opportunities. These continents were not inhabited by earlier hominin species (like Neanderthals or Homo erectus) before the arrival of Homo sapiens. This unique historical context creates a kind of "natural experiment," allowing researchers to compare landscapes with and without the extended presence of earlier human ancestors, providing clearer insights into the specific impacts of Homo sapiens‘ arrival.
Finally, while these large-scale models paint a broad, continental picture, Professor Svenning stresses the enduring importance of granular, local studies. "And although the large models paint a broad picture, detailed local studies are absolutely essential to improve our understanding of the way humans shaped the landscape in prehistoric times," he concludes. Such localized investigations, perhaps involving high-resolution archaeological excavations, detailed paleoecological reconstructions of specific sites, and comparative analyses of adjacent areas with varying human presence, will be crucial for refining our understanding of this ancient and intricate human-environment dance. The revelation that prehistoric Europe was not a pristine wilderness, but a landscape actively shaped by its earliest human inhabitants, fundamentally alters our perception of history and compels us to rethink the very definition of "natural" ecosystems.