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

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

More than 300 different mammal species have been eradicated by human activities. The new research calculates the total unique evolutionary history that has been lost as a result at a startling 2.5bn years.

Furthermore, 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 5-7 million years for the natural world to recover.

Many scientists think a sixth mass extinction of life on Earth has begun, propelled by human destruction of wildlife, and 83% 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.

The new 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.

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. Losing elephants would therefore be like chopping a large branch off the tree of life, said Davis, whereas losing a shrew species would be like trimming off a small twig.

From the rise of modern humans to the year 1500,2bn years of evolutionary history was lost due to mammal extinctions, the researchers calculated. Since 1500, another 500m years has been lost. If the current high rate of extinctions continues for 50 years, a further 1.8bn years of phylogenetic diversity will disappear, the scientists found.

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