The evidence is mounting: humans were responsible for the extinction of large mammals

The debate has raged for decades: was it humans or climate change that caused many species of large mammals, birds and reptiles to disappear from the Earth over the past 50,000 years?

By “large” we mean animals that weighed at least 45 kilograms, also called megafauna. At least 161 species of mammals became extinct during this period. This number is based on the remains found so far.

The largest of these were hit hardest: land-dwelling herbivores that weighed more than a ton, the megaherbivores. Fifty thousand years ago, there were 57 species of megaherbivores. Today, only 11 remain. These remaining 11 species have also seen drastic declines in their populations, but not to the point of complete extinction.

A research group from the Center for Ecological Dynamics in a Novel Biosphere (ECONOVO) at the Danish National Research Institute at Aarhus University now concludes that many of these vanished species were driven to extinction by humans.

They present this conclusion in a review article published at the invitation of the journal Cambridge Prisms: ExtinctionA review article synthesizes and analyzes existing research within a particular field.

In this case, the researchers from Aarhus University combined several areas of research, including studies directly related to the extinction of large animals, such as:

• The timing of species extinctions
• The animals’ dietary preferences
• Climate and habitat requirements
• Genetic estimates of past population sizes
• Evidence of human hunting

In addition, they contain a wide range of research from other disciplines that is necessary to understand the phenomenon, such as:

• Climate history of 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, including dietary preferences

Climate change played a smaller role

The dramatic climate changes during the last interglacial and glacial periods (known as the late Pleistocene, from 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 large animals, especially the largest.

An important observation is that the preceding, equally dramatic ice ages and interglacials of the past few million years did not cause selective loss of megafauna. Especially at the beginning of the ice ages, the new cold and dry conditions caused large-scale extinctions in some regions, such as trees in Europe. However, there were no selective extinctions of large animals.

“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, selective extinctions, arguing against a major role for climate in megafauna extinctions,” says Professor Jens-Christian Svenning, who leads ECONOVO and is the lead author of the paper.

He adds: “Another important pattern arguing against a role for climate is that recent megafauna extinctions hit just as hard in climatically stable areas as in unstable areas.”

Effective hunters and vulnerable giants

Archaeologists have found traps specifically designed for very large animals. Isotope analyses of ancient human bones and protein residues from spear points show that they hunted and ate the largest mammals.

Svenning adds: “Early modern humans were effective hunters of even the largest animal species and clearly had the ability to reduce populations of large animals. These large animals were and are particularly vulnerable to overexploitation because they have long gestations, produce few offspring at a time, and take many years to reach sexual maturity.”

The analysis shows that human hunting of large animals such as mammoths, mastodons and giant sloths was widespread and consistent across the globe.

It also shows that the species became extinct at very different times and at different rates around the world. In some local areas it happened quite quickly, while in others it took over 10,000 years. But everywhere it happened after modern humans arrived, or in the case of Africa, after cultural advances among humans.

Species became extinct on every continent except Antarctica and in all types of ecosystems, from tropical forests and savannas to Mediterranean and temperate forests and steppes and Arctic ecosystems.

“Many of the extinct species were able to thrive in different types of environments. Therefore, their extinction cannot be explained by climate changes that caused the disappearance of a specific ecosystem type, such as the mammoth steppe, which also housed only a few megafauna species,” Svenning explains.

“Most species lived in 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 major ecological consequences. Large animals play a central role in ecosystems by influencing vegetation structure (e.g. the balance between dense forests and open areas), seed dispersal and nutrient cycling. Their disappearance has led to 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 the ecological balance and support the biodiversity that evolved in megafauna-rich ecosystems,” Svenning said.