Humans are exterminating mammals so quickly that evolution would need five million years to recover, a scientific study has reported. People on Earth have wiped out so many mammals so that the planet Earth will need 5 million years to evolve replacements, a study concluded.
Humans will cause so many mammal species to go extinct in the next 50 years that the planet’s evolutionary diversity won’t recover for 3 to 5 million years, a team of researchers has found.
The Earth may be entering its sixth mass extinction: an era in which the planet’s environments change so much that most animal and plant species die out.
The International Union for the Conservation of Nature predicts that 99.9 percent of critically endangered species and 67 percent of endangered species will be lost within the next 100 years.
The five other times a mass extinction has occurred over the past 450 million years, natural disasters were to blame. But now, human activity is killing mammal species.
In a study published Monday in the journal PNAS, scientists from Aarhus University in Denmark calculated how fast extinctions are happening, and how long it would take for evolution to bring Earth back to the level of biodiversity it currently has.
The scientists concluded that in a best-case scenario, nature will need 3-5 million years to get back to the level of biodiversity we have on Earth today. Returning to the state Earth’s animal kingdom was in before modern humans evolved would take 5-7 million years.
5 million years to recover
Danish and Swedish researchers said that many mammal species would be extinct during the next five decades but nature need 3 to 5 million years to recover.
The study published on Monday in the Proceedings of the National Academy of Sciences showed that the sixth mass extinction was happening now, not caused by natural disasters but by humans.
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.
Some species face extinction.
Researchers said that not all species have the same significance. Some extinct animals with few close relatives, like the Australian leopard-like marsupial lion or the strange South American Macrauchenia (imagine a lama with an elephant trunk) were evolutionary distinct lineages.
Therefore, when these animals became extinct, they took whole branches of the evolutionary tree of life with them, so the unique ecological functions and the millions of years of evolutionary history were lost, according to the study.
“There are hundreds of species of shrew, so they can weather a few extinctions. There were only four species of a saber-toothed tiger; they all went extinct,” said paleontologist Matt Davis from Aarhus University.
The researchers came up with a best-case scenario of the future, where humans have stopped destroying habitats and eradicating species.
However, even with this overly optimistic scenario, it will take mammals 3 to 5 million years just to diversify enough to regenerate the branches of the evolutionary tree that they are expected to lose over the next 50 years.
THE BOTTOM LINE: Indeed, our actions have been far more destructive than if we’d just killed off species at random. That’s because, as another group showed earlier this year, we have disproportionately targeted the largest species. They used to be giant ground sloths and car-size armadillos; they’re all gone. There used to be six species of elephant-like mammals in North America alone; now there are just three left in the entire world.
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