The debate has raged for decades: Was it humans or climate change that led to the extinction of many large mammals, birds, and reptiles over the past 50,000 years? Researchers from the Danish National Research Foundation’s Center for Ecological Dynamics in a Novel Biosphere (ECONOVO) at Aarhus University now conclude that many of these species were hunted to extinction by humans. By “large,” we mean animals weighing at least 45 kilograms – known as megafauna. At least 161 mammal species were driven to extinction during this period, based on remains found so far.
MEGAHERBIVORES WERE THE HARDEST HIT
The largest of them, land-dwelling herbivores weighing over a ton, suffered the most. Fifty thousand years ago, there were 57 species of megaherbivores. Today, only 11 remain. These surviving species have also experienced drastic population declines, though not to the point of complete extinction. This conclusion is detailed in a review article published in the scientific journal Cambridge Prisms: Extinction, which synthesizes and analyzes existing research on this topic.
INTERDISCIPLINARY RESEARCH APPROACH
The researchers from Aarhus University incorporated several research fields to understand the extinction of large animals, including:
- Timing of species extinctions
- Animals’ dietary preferences
- Climate and habitat requirements
- Genetic estimates of past population sizes
- Evidence of human hunting
They also included studies from other relevant fields, such as:
- Climate history over the past 1-3 million years
- Vegetation history over the past 1-3 million years
- Evolution and dynamics of fauna over the past 66 million years
- Archaeological data on human expansion and lifestyle
CLIMATE CHANGE PLAYED A LESSER ROLE
Dramatic climate changes during the late Pleistocene (130,000 to 11,000 years ago) certainly affected populations and distributions of both large and small animals and plants worldwide. However, significant extinctions were observed only among the largest animals.
PREVIOUS ICE AGES DID NOT SELECTIVELY AFFECT MEGAFAUNA
An important observation is that previous dramatic ice ages and interglacials over the past couple of million years did not cause a selective loss of megafauna. While new cold and dry conditions caused large-scale extinctions in some regions, such as trees in Europe, there were no selective extinctions of large animals.
UNIQUE EXTINCTIONS IN THE PAST 50,000 YEARS
“The large and very selective loss of megafauna over the last 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 the megafauna extinctions,” says Professor Jens-Christian Svenning, lead author of the article. He adds, “Another significant pattern that argues against a role for climate is that the recent megafauna extinctions hit just as hard in climatically stable areas as in unstable areas.”
EFFECTIVE HUNTERS AND VULNERABLE GIANTS
Archaeologists have found traps designed for very large animals, and isotope analyses of ancient human bones and protein residues from spear points show that early modern humans hunted and ate the largest mammals.
HUMAN HUNTING WIDESPREAD AND CONSISTENT
“Early modern humans were effective hunters of even the largest animal species and clearly had the ability to reduce the populations of large animals. 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,” says Svenning.
The analysis shows that human hunting of large animals such as mammoths, mastodons, and giant sloths was widespread and consistent across the world. Species went extinct at different times and rates, but always after modern humans arrived, or in Africa’s case, after cultural advancements among humans.
EXTINCTIONS IN ALL TYPES OF ENVIRONMENTS
Species went 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 could thrive in various types of environments. Therefore, their extinction cannot be explained by climate changes causing the disappearance of a specific ecosystem type, such as the mammoth steppe – which also housed only a few megafauna species,” explains Svenning. “Most of the species existed under temperate to tropical conditions and should actually have benefited from the warming at the end of the last ice age.”
CONSEQUENCES AND RECOMMENDATIONS
The researchers point out that the loss of megafauna has had profound ecological consequences. Large animals play a central role in ecosystems by influencing vegetation structure, seed dispersal, and nutrient cycling. Their disappearance has resulted in significant changes in ecosystem structures and functions.
“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 in ecosystems rich in megafauna,” says Svenning.
