Humans, Not Climate Change, To Blame For Ice Age Animal Extinction

Jennifer Carole via flickr

Our last glacial period lasted from about 115,000-12,500 years ago. By the end, 177 large mammal species had gone extinct. There has been considerable debate over the last half century regarding what caused the loss of these animals, including saber-tooth cats, mastadons, and giant sloths. While many have argued that these animals simply weren’t able to adapt to the warmer climate, others blame human activity. A new study led by Jens-Christian Svenning of Aarhus University has strongly suggested that humans are squarely responsible for the disappearance of megafauna during the last 100,000 years. The results have been published in the Proceedings of the Royal Society B.

For this study, the researchers focused on megafauna, which is categorized as animals weighing at least 10 kg (22 lbs) that lived in the last 132,000 years. They also identified the regions where these animals lived, comparing the data with climate and human activity. While there are invariably going to be animals lost after a great climate change such as the ending of an ice age, the loss of megafauna that followed the most recent glacial event is an anomaly when compared to the ending of other ice ages.

“Our results strongly underline the fact that human expansion throughout the world has meant an enormous loss of large animals,” co-author Søren Faurby said in a press release.

The team had identified that out of the 177 large mammals that went extinct, 62 species were native to South America, 43 from North America, 38 from Asia, 26 from Australia and the surrounding region, 19 from Europe, and 18 of the extinct species were from Africa. Surprisingly,  the areas where the animals went extinct spanned all climate regions, even the warmer regions that hadn’t been particularly affected by the ice age. While there is a slight correlation between the changing climate and the animals dying out, the researchers feel it isn’t nearly strong enough to explain such a drastic series of events across the globe. If anything, it would only explain the extinctions in Eurasia.

"The significant loss of megafauna all over the world can therefore not be explained by climate change, even though it has definitely played a role as a driving force in changing the distribution of some species of animals,” lead author Christopher Sandom explained. “Reindeer and polar foxes were found in Central Europe during the Ice Age, for example, but they withdrew northwards as the climate became warmer.”

Unfortunately, the correlation between extinctions and human activity was quite strong. Hunting activity is believed to be the root cause of the animals’ extinction, through both direct and indirect methods. Humans either hunted the animals themselves, or competed with them for smaller prey. With the animals’ food source gone, they wouldn’t be able to sustain their populations.

"We consistently find very large rates of extinction in areas where there had been no contact between wildlife and primitive human races, and which were suddenly confronted by fully developed modern humans (Homo sapiens). In general, at least 30% of the large species of animals disappeared from all such areas,” stated Svenning.

The extinction of these ice age animals is not completely unlike the overhunting that has threatened the lives of modern megafauna, including sharks, rhinoceroses, elephants, and big cats, such as the tiger. These results also support a paper published in March in which genetic analyses revealed that humans drove Moas to extinction so quickly, it didn’t even have time to affect the birds’ biodiversity. An unrelated study a week later suggested that woolly mammoths suffered inbreeding depression, likely due to a declining population from human hunting, making severe birth defects common before the species went extinct.

[Header image “Spring Break 2013: Day 4” by Jennifer Carole via flickr, used in accordance with CC BY-ND 2.0 and has been cropped to fit]

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