Is the great mystery of the megafauna revealed? Humans really drove the ancient giants to extinction

AARHUS, Denmark – Imagine a world where elephants roam Europe, giant ground sloths roam the Americas, and car-sized armadillos burrow in the grasslands of South America. This wasn’t a 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 event that reshaped life on our planet? It’s a question that has puzzled scientists for more than 200 years. Now, an international team of researchers has conducted an exhaustive review of the evidence, concluding that prehistoric humans were probably the main culprits behind the downfall of Earth’s giants.

The study, led by scientists from the Danish National Research Foundation’s Center for Ecological Dynamics in a New Biosphere (ECONOVO) at Aarhus University, analyzed megafauna extinction patterns across continents and time periods. They found that large animals began to disappear soon after humans arrived in new regions, with the highest extinction rates where humans were younger.

“The massive and highly selective loss of megafauna over the past 50,000 years is unique over the past 66 million years. Previous periods of climate change did not lead to large, selective extinctions, which argues against a major role for climate in megafauna extinctions,” says Professor Jens-Christian Svenning, lead author of the study, in a statement.

The researchers point out that climate change, long considered a possible cause of the extinctions, does not adequately explain the observed patterns. While the late Pleistocene epoch saw significant climate changes, these were no more extreme than previous glacial cycles that did not result in mass extinctions.

“Another important pattern that argues against a role for climate is that recent megafauna extinctions hit climate-stable areas as hard as unstable areas,” Svenning adds.

Furthermore, megafauna losses were highly selective, mostly affecting only the largest species. Smaller animals, plants and marine life were largely untouched. This size bias is consistent with what we would expect from human hunting pressure, not climate change.

The study reveals that at least 161 species of mammals were driven to extinction during this period, based on remains found so far. The biggest animals were hit the hardest – ground-dwelling herbivores weighing over a ton, known as megaherbivores. Fifty thousand years ago, there were 57 species of megaherbivores. Today, only 11 remain, where even these survivors have suffered a drastic population decline.

Interestingly, regions where humans had a longer evolutionary history with large animals saw less severe extinction events. In Africa and parts of Asia, where hominins had been present for millions of years, fewer megafauna species went extinct than in the Americas and Australia. This suggests that animals in Africa and Asia may have developed behaviors to avoid human predators over time. Researchers found evidence of human hunting skills in the archaeological record.

“Early modern humans were efficient hunters of even the largest animal species and undoubtedly had the ability to reduce large animal populations,” 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 profound impacts that are still shaping our world today. Large herbivores such as mammoths and ground sloths played crucial roles in maintaining open habitats and distributing nutrients across landscapes. Their disappearance is likely to contribute to the spread of forests and changes in fire regimes in many regions.

“Species became extinct on all continents except Antarctica and in all types of ecosystems, from tropical forests and savannas to Mediterranean and temperate forests and steppes to arctic ecosystems. Many of the extinct species can thrive in different types of environments. Therefore, their extinction cannot be explained by climate change causing the extinction of a specific type of ecosystem, such as the mammoth steppe – which also housed only a few megafauna species,” Svenning points out.

The authors argue that understanding this extinction event is essential 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 “re-exchange,” reintroducing 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 ecological balances and support biodiversity, which evolved into megafauna-rich ecosystems,” concludes Svenning.

The study is published in the journal Cambridge Prisms: Extinction.

METHODOLOGY

The researchers conducted an extensive literature review, examining 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 extinctions, including climate change and human impacts, against observed patterns. Their review covered 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.

Results

The study found that megafauna extinctions were global in scope but varied in intensity across regions. They were strongly biased toward larger species and temporally associated with human arrivals in new areas. The disappearances were not well explained by climate change alone. The researchers noted that at least 161 mammal species were driven to extinction during this period, with land-dwelling herbivores weighing over a ton (megaherbivores) being the most affected.

RESTRICTIONS

Among the potential limitations of this study, 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. Furthermore, the complex interactions between humans, climate and ecosystems are difficult to fully disentangle, especially over such long time scales.

Discussion & Relationship

The researchers conclude that human hunting and ecosystem modification were likely the main drivers of the late Quaternary megafauna extinction. They argue that this event marks an early example of human-driven environmental change on a global scale. The study points out 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, altering vegetation structures, seed dispersal patterns, and nutrient cycling. The authors emphasize the importance of understanding past extinctions to inform modern conservation efforts. They suggest that restocking with large animals can help restore lost ecological functions and support biodiversity in ecosystems that evolved with megafauna.