Early humans hunt the woolly mammoth. More and more research shows that this species—and at least 46 other species of megaherbivores—were driven to extinction by humans. (CREDIT: Engraving by Ernest Gris, photographed by William Henry Jackson. Courtesy of Getty’s Open Content)
AARHUS, Denmark — Imagine a world where elephants roamed Europe, giant ground sloths roamed the Americas, and armadillos the size of cars burrowed into the grasslands of South America. It wasn’t some fantasy realm from a Hollywood movie – it was Earth just 50,000 years ago. But then something happened. These megafauna—animals weighing over 100 pounds—began to disappear. By 10,000 years ago, most were gone forever.
What caused this mass extinction that reshaped life on our planet? It’s a question that has puzzled scientists for over 200 years. Now, an international team of researchers has conducted an exhaustive review of the evidence and concluded that prehistoric humans were probably the main culprits in the fall of the earth’s giants.
The study, led by scientists from the Danish National Research Foundation’s Center for Ecological Dynamics in the New Biosphere (ECONOVO) at Aarhus University, analyzed megafauna extinction patterns across continents and time periods. They found that large animals began disappearing shortly after humans arrived in new areas, with extinction rates highest where humans were newest.
“The large and highly selective loss of megafauna over the past 50,000 years is unique in the past 66 million years. Previous periods of climate change did not lead to large-scale selective extinctions, arguing against a major role for climate in megafauna extinctions,” says Professor Jens-Christian Svenning, lead author of the study, in a statement.
Scientists point out that climate change, long considered a potential cause of extinction, does not adequately explain the observed patterns. Although the Late Pleistocene epoch saw significant climate shifts, they were no more extreme than previous glacial cycles that did not lead to mass extinctions.
“Another significant pattern that argues against a role for climate is that recent megafauna extinctions have hit climate-stable areas as hard as unstable areas,” Svenning adds.
In addition, megafauna losses were highly selective, primarily affecting only the largest species. Smaller animals, plants and marine life were largely untouched. This size bias is what we would expect from human hunting pressure, not climate change.
The study reveals that at least 161 species of mammals went extinct during this period based on the remains found so far. The biggest animals were hit the hardest – terrestrial herbivores weighing over a ton, known as mega-herbivores. Fifty thousand years ago, 57 species of megaherbivores lived here. Today, only 11 remain, with even those survivors experiencing drastic population declines.
Interestingly, less severe extinction events occurred in areas where humans had a longer evolutionary history with large animals. In Africa and parts of Asia, where hominins were present for millions of years, fewer species of megafauna became extinct compared to the Americas and Australia. This suggests that animals in Africa and Asia may have evolved behaviors to avoid human predators over time. Scientists have found evidence of human hunting prowess in the archaeological record.
“Early modern humans were efficient hunters of even the largest animal species and clearly had the ability to reduce populations of large animals,” notes Svenning. “These large animals were and are particularly vulnerable to overexploitation because they have long gestation periods, produce very few offspring at a time, and take many years to reach sexual maturity.”
The loss of these ecosystem giants had a profound impact that continues to shape our world today. Large herbivores such as mammoths and ground sloths played a vital role in maintaining open habitats and dispersing nutrients across the landscape. Their disappearance likely contributed to forest expansion and changes in fire regimes in many regions.
“Species have become extinct on every continent except Antarctica and in every type of ecosystem, from tropical forests and savannas to Mediterranean and temperate forests and steppes to arctic ecosystems. Many extinct species were able to thrive in different types of environments. Therefore, their extinction cannot be explained by climate changes, which will cause the disappearance of a specific type of ecosystem, such as the mammoth steppe – where only a few species of megafauna were also found,” emphasizes Svenning.
The authors argue that understanding this extinction event is crucial as we face a biodiversity crisis today. By recognizing the long history of human impact on animal populations, we can better inform conservation efforts. They even suggest “rewilding,” the reintroduction of large animals to restore lost ecological functions, as a potential conservation strategy.
“Our results highlight the need for active conservation and restoration efforts. By reintroducing large mammals, we can help restore the ecological balance and support the biodiversity that has evolved in ecosystems rich in megafauna,” concludes Svenning.
The study is published in the journal Cambridge Prisms: The Demise.
Methodology
The researchers conducted an extensive literature review and examined evidence from paleontology, archaeology, genetics and ecology. They analyzed megafauna extinction patterns across different continents, time periods and body size classes. The team also evaluated various hypotheses for the extinction, including climate change and human impacts, against observed patterns. Their review spanned several research areas, including studies on the timing of species extinctions, animal dietary preferences, climate and habitat requirements, genetic estimates of past population sizes, and evidence of human hunting.
Result
The study found that megafauna extinctions were global in scale but varied in intensity across regions. They were strongly biased towards the largest species and temporally associated with the arrival of man in new areas. The extinctions were not well explained by climate change alone. The researchers found that at least 161 species of mammals went extinct during this period, with land-dwelling herbivores weighing over a ton (mega-herbivores) being the most severely affected.
Limitations
Among the possible limitations of this study is that the fossil record is incomplete, especially for smaller species, which may bias our understanding of extinction patterns. The dating of extinction events and human arrivals can be imprecise, making it difficult to establish precise temporal relationships. Moreover, it is difficult to fully unravel the complex interactions between people, climate and ecosystems, especially over such a long time horizon.
Discussion & Takeaways
The researchers concluded that human hunting and ecosystem modification were likely the main drivers of megafauna extinction in the Late Quaternary. They argue that this event represents an early example of human-driven environmental change on a global scale. The study highlights that humans have been shaping ecosystems for tens of thousands of years and that large animals are particularly vulnerable to human impacts. The loss of megafauna had cascading effects on landscapes and ecosystems, changing vegetation structure, seed dispersal patterns and nutrient cycling. The authors emphasize the importance of understanding past extinctions to inform modern conservation efforts. They suggest that survival with large animals can help restore lost ecological functions and promote biodiversity in ecosystems that evolved with megafauna.