Monday, 27 May, 2019

Scientists said that the Earth is waiting for another great extinction

Mammals cannot evolve fast enough to escape current extinction crisis Research: Mammals cannot evolve fast enough to escape current extinction crisis —
Sandy Nunez | 19 October, 2018, 05:57

It will take mammals 5-7 million years to rebuild diversity to its level before humans evolved.

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.

Like many scientists, Davis believes the world is now in the midst of a sixth mass extinction, also known as the anthropocene extinction or one caused by human activity.

A team of researchers believes human-induced extinction on Earth is occurring much faster than evolution.

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 now has. However, even with this overly optimistic scenario, it will take mammals 3-5 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. 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.

Evolution is the planet's defense mechanism against the loss of biodiversity.

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. In those cases, evolution allowed new species to replace those that were lost.

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Researchers from Aarhus University and the University of Gothenburg examined a massive database of both existing and extinct mammals. 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.

The team considered a few scenarios: mammals start to recover immediately - a situation that would require a dramatic change to conservation norms-or after 20, 50 or 100 years of current conservation efforts. Since then, humans have helped erase another 500 million years ― and an additional 1.8 billion years could be lost in the next five decades if the high rate of mammal extinctions continues. The five million will go on restoration of the ice age megafauna. Now, researchers say that recovering the lost biodiversity will take millions of years. Matt Davis, a paleontologist at Aarhus University who led the study, cited the shrew as an example. Today, meanwhile, "there are hundreds of species of shrew, so they can weather a few extinctions". In contrast, "there were only four species of sabre-toothed tiger; they all went extinct".

"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.

For the study, Davis and his colleagues focused not just on the number of species that have gone extinct but also on how much evolutionary history they represent (or the amount of time each species had spent evolving before it was wiped out).

And we have done such a convincing job, scientists are labelling this the sixth mass extinction. Asian elephants' chance of making it to the 22nd century is less than 33%, the study found.

"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".