A study led by Alan Cooper, a paleogeneticist at the University of Adelaide in Australia, has looked at the fossils of ancient mammoths, sloths, and other megafauna, and it determines that the reason for the extinction of such creatures has more to do with climate change than it has to do with hunting. While human activity may still have been a big factor in the climate change, this recent study sheds more light on the disappearance of so many species thousands of years ago. Science writes:
About 30,000 years ago, mammoths, giant sloths, and other massive mammals roamed the earth. Twenty thousand years later they were all gone. Some researchers blame human hunting, but a new study claims that abrupt shifts in climate set in motion a downward spiral for many of these species, one that humans aggravated. The results, the authors say, are a warning to modern humans that, if not slowed, current warming could doom many more species.
Until recently, researchers relied primarily on fossils to assess the rise and fall of big mammals over the past 60,000 years. But a team led by Alan Cooper, a paleogeneticist at the University of Adelaide in Australia, added ancient DNA—isolated from the same fossils—to the mix. Based on how diverse a species’ DNA is at a given site, he and his colleagues can estimate how plentiful the animals were at a particular point in time. They compiled material from thousands of sites across North America and Eurasia, focusing on DNA from ancient mammal bones that had been analyzed by radio carbon methods to determine their ages.
The analysis showed that various species were disappearing at different times from different sites over the past 60,000 years. Sometimes they were replaced by new populations moving in as the climate cooled; other times they were not—and the permanent loss may have represented one of the large mammals' extinction.
"This abrupt warming had a profound impact on climate that caused marked shifts in global rainfall and vegetation patterns," Alan Cooper, the lead author and director of the Australian Centre for Ancient DNA, said. "Even without the presence of humans we saw mass extinctions. When you add the modern addition of human pressures and fragmenting of the environment to the rapid changes brought by global warming, it raises serious concerns about the future of our environment."
