Well it was nice while it lasted – we've had a whole three weeks of humans being cleared of responsibility for the extinction of the woolly mammoth, and now it looks like it's back to being partially our fault after all. A new paper makes the case that only a combination of human influence and a changing climate can explain mammoths’ decline to extinction. More broadly, the authors conclude species seldom go extinct from one cause alone.
Few conflicts in science are as bitter or as long-lasting as the question of human responsibility for the extinction of big animals outside Africa. So it's not really surprising the claim that one of the largest land animals to co-exist with humans died out from climate change would not stand unchallenged.
Dr Damien Fordham of the University of Adelaide led a team that took a broad view of woolly mammoth extinction, using data on what we know about mammoths' presence or absence across their original realm. In Ecology Letters they report human hunting pressure started the mammoth's decline 20,000 years ago. By looking at the conditions under which localized extinctions occurred the authors identified what they think are the requirements for mammoths to die out. They conclude that without human influence, the climate change over the last 10,000 years would have been insufficient to end these great beasts entirely.
“Our research shows that humans were a crucial and chronic driver of population declines of woolly mammoths, having an essential role in the timing and location of their extinction,” Fordham said in a statement.
Extinctions, like the dodo, that closely follow human arrival are easy to blame on us. Equally, animals that died out before there are signs humans reached them can probably be safely attributed to something else – usually climate change. Other cases are much more difficult to untangle, but Fordham and colleagues believe by identifying the circumstances in which localized extinctions occur the two can be separated. They explored 90,000 scenarios and, Fordham told IFLScience, “We can’t replicate the [mammoth] fossil record without an important role for humans.”
“Our analyses strengthens and better resolves the case for human impacts as a driver of population declines and range collapses of megafauna in Eurasia during the Late Pleistocene,” co-author Dr David Nogués-Bravo from the University of Copenhagen said. “And shows that species extinctions are usually the result of complex interactions between threatening processes.”
Although the last known mammoths died out 4,000 years ago, these were restricted to Wrangel island. It had been thought continental mammoths were extinct 4,000 years earlier still. However, Fordham and Nogués-Bravo’s modeling suggests the hairy beasts should have survived in certain poorly-explored Siberian refugia as long as they did on Wrangel.
When the team reached this conclusion they lacked field evidence to support it. Ironically, however, the paper published last month, while reaching entirely different conclusions about the case of the mammoths’ extinctions also provided DNA evidence for mammoths’ persistence in just the sort of places this paper predicted.
The research is not directly applicable to other megafauna species without a similarly detailed fossil record. However, Fordham told IFLScience it supports the conclusion “Extinctions are unlikely to occur from a single driver. It is usually because of multiple drivers working synergistically.”
Efforts are underway to clone mammoths and potentially bring them back. There is much debate both about the technical practicality and ethics of this. Some people consider the case for “de-extinction” much stronger where humans were the cause of the original extinction. However, Fordham told IFLScience he thinks “We have such an impending problem in terms of conserving existing biodiversity, resources need to focus on that.”