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Climate change caused extinction of woolly mammoths, University of Cambridge scientists prove



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Woolly mammoths went extinct after five million years of roaming the Earth because of climate change, scientists have proven.

The huge hairy cousins of today’s elephants died out nearly 4,000 years ago, but the question of how has been hotly debated.

A woman with three woolly mammoths
A woman with three woolly mammoths

Now geneticists who analysed ancient environmental DNA have shown it was because when the icebergs melted, it became far too wet for them to survive as the vegetation they fed on was practically wiped out.

Prof Eske Willerslev, a fellow of St John’s College at the University of Cambridge, and director of The Lundbeck Foundation GeoGenetics Centre, University of Copenhagen, led the 10-year research project.

“Scientists have argued for 100 years about why mammoths went extinct. Humans have been blamed because the animals had survived for millions of years without climate change killing them off before, but when they lived alongside humans they didn’t last long and we were accused of hunting them to death.

“We have finally been able to prove was that it was not just the climate changing that was the problem, but the speed of it that was the final nail in the coffin – they were not able to adapt quickly enough when the landscape dramatically transformed and their food became scarce.

“As the climate warmed up, trees and wetland plants took over and replaced the mammoth’s grassland habitats. And we should remember that there were a lot of animals around that were easier to hunt than a giant woolly mammoth – they could grow to the height of a double decker bus!”

For the study, published in Nature, the team used DNA shotgun sequencing to analyse environmental plant and animal remains, including urine, faeces and skin cells, taken from soil samples collected over 20 years from sites in the Arctic where mammoth remains were found.

Prof Willerslev believes soil will replace fossils for such studies because sequencing DNA from soil samples provides superior detail. Illumina sequencers were used to analyse the DNA from 50,000 years ago.

Herds of mammoths, reindeer and woolly rhinoceroses thrived in cold and snowy conditions during several Ice Ages.

A lot of vegetation grew, in spite of the cold. Grass, flowers, plants and small shrubs would have been eaten by the vegetarian mammoths, which are thought to have used their tusks to shovel snow aside and their trunks to uproot tough grasses.

Their enormous size is put down to their need for huge stomachs to digest the grass.

They lived on all continents except Australia and South America and could roam the equivalent of twice around the world in their lifetime.

Populations of them are known to have initially survived the end of the last Ice Age lived in small pockets off the coasts of Siberia and Alaska – on Wrangel Island and St Paul Island.

The latest research found they lived longer elsewhere too and showed the breeds of mammoths on both the islands were closely related, despite being geographically separated. The sequencing technology was also used to sequence the DNA of 1,500 Arctic plants for the very first time too.

The researchers, including Prof Eske Willerslev, of St John's College, Cambridge
The researchers, including Prof Eske Willerslev, of St John's College, Cambridge

Dr Yucheng Wang, first author of the paper and a research associate at the Department of Zoology, University of Cambridge, said: “The most recent Ice Age – called the Pleistocene – ended 12,000 years ago when the glaciers began to melt and the roaming range of the herds of mammoths decreased. It was thought that mammoths began to go extinct then but we also found they actually survived beyond the Ice Age all in different regions of the Arctic and into the Holocene – the time that we are currently living in – far longer than scientists realised.

“We zoomed into the intricate detail of the environmental DNA and mapped out the population spread of these mammals and show how it becomes smaller and smaller and their genetic diversity gets smaller and smaller too, which made it even harder for them to survive.

“When the climate got wetter and the ice began to melt it led to the formation of lakes, rivers, and marshes. The ecosystem changed and the biomass of the vegetation reduced and would not have been able to sustain the herds of mammoths. We have shown that climate change, specifically precipitation, directly drives the change in the vegetation – humans had no impact on them at all based on our models.”

A woolly mammoth
A woolly mammoth

Mammoths were still around when the pyramids were being built, and humans lived alongside them for at least 2,000 years.

Prof Willerslev said: “This is a stark lesson from history and shows how unpredictable climate change is – once something is lost, there is no going back. Precipitation was the cause of the extinction of woolly mammoths through the changes to plants. The change happened so quickly that they could not adapt and evolve to survive.

Prof Eske Willerslev, of St John's College, Cambridge
Prof Eske Willerslev, of St John's College, Cambridge

“It shows nothing is guaranteed when it comes to the impact of dramatic changes in the weather. The early humans would have seen the world change beyond all recognition – that could easily happen again and we cannot take for granted that we will even be around to witness it. The only thing we can predict with any certainty is that the change will be massive.”

Read more on Prof Willerslev’s research

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