A team of researchers believes human-induced extinction on Earth is occurring much faster than evolution. They expect that in the next 50 years, our planet’s evolutionary diversity will be so destroyed that it will take it millions of years to recover.
They argue that Earth entering its sixth mass extinction, an event in which the planet’s environments change to the point that life can’t continue as it should and most animal and plant species die. The International Union for the Conservation of Nature estimates that 99% of critically endangered species and 67% of endangered species will die out within the next 100 years.
Natural disasters can be blamed for the previous five mass extinctions, but researchers say humans would be the main culprit in the sixth mass extinction on Earth because human activity has begun killing mammal species.
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Extinction on Earth happening faster than evolution?
Scientists from Aarhus University in Denmark published a study in the journal Proceedings of the National Academy of Sciences of the United States of America. They calculated the pace of extinction on Earth and how much faster than evolution it could be occurring. Their main question is how long it would take for evolution to restore Earth’s biodiversity to how it is currently.
According to their calculations, in the best-case scenario, nature would need 3 million to 5 million years to get back to the level of biodiversity we have on Earth today. They estimate that if Earth were to return to the state it was in before modern humans evolved, it would take 5 million to 7 million years.
Scientists have long believed that evolution is the planet’s way of defending itself from the loss of biodiversity. When habitats and climates change, species which die out are replaced by newly-emerging species. Nevertheless, it takes time for new species to fill in the gaps.
To make their calculations, the scientists from Aarhus University referred to a database which contains extinct mammal species and mammals that went extinct as humans spread out. After combining that data with information about extinctions they expect in the coming years, they used advanced simulations to see how long it could take for extinction on Earth to be surpassed by evolution.
Even in the best-case scenario, the recovery time depends on how quickly mammals start to recover. If the extinction rate doesn’t begin to fall in the next 20 to 100 years, the scientists say extinction on Earth will likely occur faster than evolution and more species will disappear, causing a much greater loss in biodiversity.
Matt Davis, an Aarhus University paleontologist who was leading the study, pointed to the shrew as an example. There are hundreds of species of shrew, so if half of them should become extinct, it wouldn’t kill out the entire shrew population on Earth. On the other hand, scientists say there were only four species of saber-toothed tigers, so when they became extinct, many years of evolution disappeared with them.
“Large mammals, or megafauna, such as giant sloths and sabre-toothed tigers, which became extinct about 10,000 years ago, were highly evolutionarily distinct,” Davis said in a press release. “Since they had few close relatives, their extinctions meant that entire branches of Earth’s evolutionary tree were chopped off.”
“We now live in a world that is becoming increasingly impoverished of large wild mammalian species,” Aarhus University Professor Jens-Christian Svenning said in a statement. “The few remaining giants, such as rhinos and elephants, are in danger of being wiped out very rapidly.”
Though their calculations regarding extinction on Earth are still dire, the scientists think their work could be used to figure out which endangered species are evolutionarily unique and represent the most important parts of evolutionary history on Earth. That should help them focus their efforts so that more extinctions can be avoided.