Humans May Have Driven Mammoth Extinction More Than Climate

Some 20,000 years ago, mammoths and related species remained comparatively widespread. Yet by roughly 10,000 years ago, nearly all had vanished - a remarkably rapid disappearance for animals that had flourished on Earth for millions of years.

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

However, a fresh study suggests that increasing global temperatures probably played a far smaller part in the mammoth's extinction than previously assumed.

Humans and the decline of proboscideans

The new research links the dwindling of early proboscideans - the animal order encompassing elephants, woolly mammoths (Mammuthus primigenius) and their long-snouted relatives - with the appearance 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."

A species rarely becomes extinct because of one cause alone. Instead, its continued existence can be undermined by a combination of conditions: habitats becoming steadily less hospitable, food supplies declining alongside stronger competition for them, and hunting by other species can all play a part.

Early humans are known to have hunted mammoths. Numerous mammoth bones have been discovered bearing marks from cutting tools and butchery. Even so, the extent to which this hunting contributed to the animals' downfall has remained contested.

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

Neural network analysis of mammoth extinction

For the investigation, the researchers used a neural network. They trained the algorithm to examine fossil records, measure the loss of proboscidean species and compare those declines with other environmental influences in order to identify potential causes.

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

It also assessed 17 possible influences on the populations of these animals, including climate and environmental information. Naturally, these factors included the emergence of early hominids around 1.8 million years ago and the arrival of modern humans (Homo sapiens) approximately 129,000 years ago.

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

After humans entered the picture, however, the situation deteriorated dramatically. Extinction rates climbed steeply and reached a 17-fold increase with the arrival of modern humans, regardless of the other factors involved. Indeed, climate ranked fourth among the predictors and accounted for only a modest rise in the extinction rate.

This indicates that the powerful impact of human hunting is now a leading candidate for the principal cause of proboscidean 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 study has been published in Science Advances.