Humans May Have Driven Mammoths Towards Extinction

Mammoths and the end of the Last Ice Age

Some 20,000 years ago, mammoths and related species were still fairly widespread. Yet by roughly 10,000 years ago, almost all had vanished - a remarkably abrupt disappearance after millions of years of success on Earth.

A widely accepted account has pointed to an enormous climatic shift. Earth’s latest glacial phase, the Last Ice Age, ended about 11,000 years ago.

However, new research indicates that increasing global temperatures were probably far less important to the mammoth’s disappearance than previously assumed.

The study links the dwindling of early proboscideans - the animal order encompassing elephants, woolly mammoths (Mammuthus primigenius) and other long-nosed relatives - to the arrival and expansion of early humans.

"The emergence of modern humans escalated extinction rates, causing recent diversity decline, while regional climate had a lesser impact," writes a team led by ecologist Torsten Hauffe of the University of Fribourg in Switzerland.

"Our model paves the way for an improved understanding of the intricate dynamics shaping clade diversification."

How humans may have driven proboscidean decline

A species’ extinction is rarely caused by one influence alone. Instead, its continuing survival can be undermined by a combination of circumstances, including increasingly hostile habitats, reduced food supplies, greater competition for those resources and predation from other species.

Early humans are known to have hunted mammoths. Numerous mammoth bones have been discovered with marks left by cutting tools and butchery. Even so, the extent to which hunting contributed to the animals’ extinction has remained disputed.

Hauffe and his team set out to determine whether there was a correlation between the arrival of modern humans and the mammoth’s decline.

They did so using a neural network. The researchers trained an algorithm to examine fossil records, measure the fall in proboscidean species and compare those declines with other environmental influences in order to identify possible causes.

Fossils, climate and the arrival of modern humans

The model received information from 2,118 fossils representing 175 proboscidean species that existed between 35 million and 10,000 years ago. This included morphological changes, such as variations in tusk size.

It also assessed 17 potential influences on these animals’ populations, among them climate and environmental information. Naturally, the dataset also included the emergence of early hominids around 1.8 million years ago and the appearance of modern humans (Homo sapiens) approximately 129,000 years ago.

At first, diversity was comparatively limited, although distinctive adaptations gradually appeared as populations evolved for new habitats and diets. Speciation became especially pronounced towards the close of the Neogene period, while the teeth of various species revealed considerable dietary adaptability.

After humans entered the picture, however, conditions deteriorated dramatically. Extinction rates climbed steeply and reached a 17-fold increase following the arrival of modern humans, regardless of the other factors involved. Climate, meanwhile, ranked fourth among the predictors and accounted for only a small rise in extinction rates.

This finding means that intensive hunting by humans is now a strong candidate for the principal driver behind the proboscideans’ decline.

"Our model… allows us to single out the effect of humans after accounting for all other factors, suggesting that the estimated 5- to 17-fold rate increase attributed to early and modern humans is not influenced by other factors considered here," the researchers write.

"We found that while humans exhibit the greatest impact in the past ca. 120,000 years, our results also point to a weaker yet significant influence of the human lineage at earlier times, thus supporting other studies suggesting a long-lasting detrimental anthropogenic effect on biodiversity."

The research was published in Science Advances.