DUBLIN: Humans are off the hook, it seems, for the extermination of large Ice Age mammals, according to a new study.
Climate change was the primary cause of population declines, according to a new study published in Nature today which looks at genetic data, climate data and the archaeology of six large herbivores.
“Finding a smoking gun is very difficult,” said lead author Eline Lorenzen, researcher at the Centre for GeoGenetics in the University of Copenhagen in Denmark.
“The results are more complicated that we previously thought. Our study indicates that humans played no part in the extinction of the woolly rhinoceros or the musk ox in Eurasia and that their demise can be entirely explained by climate change,” said co-author Simon Ho from the University of Sydney’s School of Biological Sciences.
Towards the end of the Late Quaternary, beginning around 50,000 years ago, Eurasia and North America lost approximately 36% and 72% of their large bodied mammals, respectively. The role of humans in this has been contentious, but it seems our ancestors were not responsible, at least not for large herbivores.
The new picture that is emerging is complicated, with a mixture of climate change, environmental change and human impacts impacting on various species. And all species react differently to their changing world, which makes things even more complex.
The herbivores studied expanded their range, and their populations rose with the colder, drier conditions after 30,000 years ago (Last Glacial Maximum), which favoured an expanse of steppe tundra. But they did not expand at the same time – it was over a space of thousands of years, said Lorenzen.
Although the researchers set out to find similarities among six large herbivores, this proved impossible. “The surprise was how difficult it was to find a common story because they all showed such different patterns,” Lorenzen said.
There is no evidence that there was a human factor in the extinction of the woolly rhino around 14,000 years ago in Siberia. Climate change was to blame, according to the study. The Eurasian Musk oxen also went extinct 2,500 years ago due to climate change, with no evidence of human pressure for the last 20,000 years.
A combination of climatic and human impacts appears to have been responsible for the extinction of the Eurasian steppe bison and wild horse. Lorenzen believes humans had a hand in the horse’s decline; the species had a huge potential range 6,000 years ago, yet it dwindled in number. At the same time, it is very common in human archaeological sites. “Humans likely played a role in the extinction of bison in Siberia,” she said.
To reveal the processes underlying population fluctuation and extinction, the researchers investigated the demographic histories of woolly rhino, woolly mammoth, wild horse, reindeer, bison and musk ox. The analyses were based on 846 radiocarbon-dated mitochondrial DNA sequences, 1,439 megafaunal bones, and 6,291 radiocarbon dated remains associated with Upper Palaeolithic human sites in Eurasia.
Lorenzen believes there are lessons to be learnt for conservation today. “Our data suggests care should be taken in making generalisations not just regarding past and present species extinctions but also those of the future,” she noted. The impacts of climate change and human encroachment on extinctions really depends on the species.
The late, and sudden, arrival of humans in North America, coincident with Late-Post Glacial warming, has strongly suggested human involvement in Post-Glacial ‘mass extinction’ there, but the story has never been convincing for Eurasia, commented Derek Yalden, zoologist from the University of Manchester in Britain. “The discovery that woolly mammoths survived so late on Wrangel, and of Irish Elk in the Urals, much later, suggests climate or habitat change, not overhunting,” he said.
“People, with flint arrows and spears, dependant on hunting, are always likely to have been limited by availability of their prey, and unlikely to have limited them, let alone exterminated them. So the idea of multiple causes, complex mixtures of climate and habitat change, always seemed more likely,” he added. “Any involvement of humans is probably coincidental, but without some measure of relative densities, I can’t see how one would make a convincing argument.”
Mike Bunce, head of the ancient DNA lab in Murdoch University in Perth, described this new multi-species approach to shed light on the question of whether humans or climate caused either local or total extinctions as “refreshing”.
“The magnitude of the ancient DNA data, carbon dating and climate modeling that has been compiled here is staggering – a veritable tour de force in the field of palaeontology – and the team should be commended for tackling the research in this fashion,” he said.
Once the data comes online, scientists can build a good picture of how these regions responded to past changes in climate, he said. “Importantly this kind of data may help us ‘retrodict’ what might happen as our own planet warms.”