At least of killing megafauna in prehistory, according to Michael Slezak in NewScientist (1 August 2015, paywall):
HUMANS were not to blame for the extinction of prehistoric giant mammals after all – global warming was the real culprit, according to new evidence.
Ever since a giant sloth was uncovered more than 200 years ago, hinting at the existence of an ancient menagerie of megafauna, our ancestors have been on trial for their extinction.
“The overwhelming evidence is that the megafauna extinctions occur around the world whenever humans turn up,” says Alan Cooper, who researches ancient DNA at the University of Adelaide in Australia. But that’s not the whole story. Look closer and the pattern emerging is that climate change is linked to extinctions, regardless of whether humans were there or not, he says.
DNA was used to find extinctions and check whether the rate changed when humans appears on the scene:
Two strands of evidence allowed the team to figure this out. First, they compiled 10 years of work on ancient DNA that had uncovered a series of “invisible” extinctions. These are events involving two or more lineages with identical skeletons but different genomes – two species of bison, say. That means if both species lived in the same area, we could not tell just from the bones that a species had gone extinct.
Secondly, they created a new ancient climate record spanning the same time period that could be reliably linked with the carbon dates from bones to show when particular extinctions happened. Usually, timelines for climate change and carbon dating are independent and difficult to link. But Cooper’s team found a marine sediment that contains a record of both past climates and microfossils, allowing them to link climate and carbon dating.
However, there are still lessons for today. Some species can shift their ranges in response to global warming – and some cannot:
While humans probably did not hunt species to extinction, farming would have disrupted landscapes and prevented species fleeing to escape the effects of climate change.
Cooper’s findings also provide a stark warning for the future, according to Brian Huntley from Durham University, UK. “Human alteration or destruction of ecosystems is so pervasive that it is clear that many species are unable to shift their ranges sufficiently rapidly to match current anthropogenic climatic changes,” he says.
The Australian Museum gives a digest of Australian megafauna here; Medical Daily covered the Australian megafauna question in a little more detail more than a year ago:
An extensive review of available evidence suggests that the enormous megafauna wandering the Australian outback thousands of years ago were wiped out by climate change, long before Aboriginal humans arrived on the continent.
“The interpretation that humans drove the extinction rests on assumptions that increasingly have been shown to be incorrect,” said lead author Stephen Wroe, an associate professor at the University of New South Wales, in a statement.
Wroe argues that most of the 88 giant animal species that once existed on the continent of Sahul, which encompassed Australia, New Guinea, and Tasmania, went extinct long before humans arrived between 45,000 and 50,000 years ago.
While humans may have been involved in the extinction of the ones that remained after their arrival, his team finds no conclusive proof.
