Fri, Oct 19, 2018 - Page 9 News List

Humanity is ‘cutting down the tree of life,’ scientists warn

Researchers say more than 300 mammal species have been eradicated by human activities

By Damian Carrington  /  The Guardian

Illustration: Mountain people

Humanity’s ongoing annihilation of wildlife is cutting down the tree of life, including the branch we are sitting on, a new analysis shows.

More than 300 mammal species have been eradicated by human activities, the researchers said.

The authors calculated the total unique evolutionary history that has been lost as a result at 2.5 billion years.

Even if the destruction of wild areas, poaching and pollution were ended within 50 years and extinction rates fell back to natural levels, it would still take 5 million to 7 million years for the natural world to recover, they said.

Many scientists think a sixth mass extinction of life on Earth has begun, propelled by human destruction of wildlife, and 83 percent of wild mammals have already gone.

The new work puts this in the context of the evolution and extinction of species that occurred for billions of years before modern humans arrived.

“We are doing something that will last millions of years beyond us,” said Matt Davis at Aarhus University in Denmark, who led the new research. “It shows the severity of what we are in right now. We’re entering what could be an extinction on the scale of what killed the dinosaurs.

“That is pretty scary. We are starting to cut down the whole tree [of life], including the branch we are sitting on right now,” Davis said.

Ecosystems around the world have already been significantly affected by the extermination of big animals, such as mammoths, he said.

The research, published in the Proceedings of the National Academy of Sciences, did not simply add up the number of lost species, as this fails to capture how unique each species is in evolutionary terms.

Instead, the researchers added up the amount of time each lost species had spent evolving since it emerged, a measure called phylogenetic diversity.

There are hundreds of species of shrew, for example, but just two species of elephant, Davis said, adding that losing elephants would therefore be like chopping a large branch off the tree of life, whereas losing a shrew species would be like trimming off a small twig.

From the rise of modern humans to the year 1500, 2 billion years of evolutionary history was lost due to mammal extinctions, the researchers calculated, adding that since 1500, another 500 million years have been lost.

If the current high rate of extinctions continues for 50 years, a further 1.8 billion years of phylogenetic diversity could disappear, they said.

There are still many mammal species left, but all of these would have to evolve for 5 million to 7 million years into the future to get back to the level of diversity present before modern humans arrived, the researchers estimated.

Davis said each lost species had its own intrinsic value, but the loss of the most distinct creatures was most damaging.

“Typically, if you have something that is off by itself, it does some job that no other species is doing,” he said.

The losses are already affecting ecosystems, particularly the vanishing of “megafauna,” he said.

These huge creatures roamed much of Earth until humans arrived and included giant cats, deer, beavers and armadillos.

“We are now living in a world without giants,” Davis said. “So the seeds of big fruit are not dispersed anymore because we don’t have mammoths or Gomphotheres or giant ground sloths eating those fruits.”

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