Prof Douglas Futuyma at Stony Brook University in the United States, who was not part of the research team, said: "They have made a dramatic and convincing statement of how much evolutionary diversity has already been lost".
It will take more than five million years to regenerate what was lost from giant Ice Age species.
The extinctions are moving too rapidly for evolution to keep up, because if mammals diversify at their normal rates, fifty years later, it will still take them 5 to 7 million years to restore biodiversity to its level before modern humans evolved, and 3 to 5 million years to reach current biodiversity levels.
There have been five upheavals over the past 450 million years when the environment on our planet has changed so dramatically that the majority of Earth's plant and animal species became extinct.
According to the study published in Proceedings of the National Academy of Sciences, iconic species such as the black rhino could become extinct within the next 50 years, while Asian elephants have only a 33% chance of surviving past this century.
Rebecca Naden/Reuters The endangered red panda, threatened by climate change and habitat destruction, has been identified by researchers as a creature with an especially rich and unique evolutionary history.
Extinction on Earth happening faster than evolution?
The researchers used a huge database that included hundreds of species of mammals that existed prior to the spread of homo sapiens. Experts have combined these data with information about the extinctions that will occur in the next 50 years, and used advanced simulation of evolution to predict how long it will take for the species recovery. If the extinction rate doesn't start falling for another 20-100 years, more species will likely disappear, causing greater diversity loss, the study said.More news: Flu shot clinic now open
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Paleontologist and lead researcher Matt Davis of Denmark's Aarhus University warned, "We are starting to cut down the whole tree [of life], including the branch we are sitting on right now". There are hundreds of species of shrew, for example, but just two species of elephant.
Regenerating 2.5 billion years of evolutionary history is hard enough, but today's mammals are also facing increasing rates of extinction. "There were only four species of sabre-toothed tiger; they all went extinct". The upcoming sixth mass extinction, however, is largely the work of humans.
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".
They inspected several scenarios, modeling the complex evolutionary relationships between existing and extinct mammals, finding that even under the most optimistic scenario, it would still take up to five million years for the mammalian life to regenerate its lost branches and twigs of the evolutionary tree.
"Although we once lived in a world of giants: giant beavers, giant armadillos, giant deer, etc., we now live in a world that is becoming increasingly impoverished of large wild mammalian species".
"It is much easier to save biodiversity now than to re-evolve it later", Davis said in a statement.
'The few remaining giants, such as rhinos and elephants, are in danger of being wiped out very rapidly'.
"Our paper particularly suggests that we should be using phylogenetic diversity more to prioritize conservation of evolutionary distinct species that are at risk of extinction", said Davis.