The sixth mass extinction, the extinction of many mammals


Since life flourished on Earth 4 billion years ago, the planet has experienced five mass extinctions of living things, one extinction after another. The latest – and best known – 65 million years olddate on which the dinosaurs disappeared with more than 70% of terrestrial species.

However, many scientists point out that we are currently immersed in the sixth extinction massivewhich has a difference compared to others: it is not a phenomenon of nature, but we ourselves, human beings, are directly responsible for it.

So much so that we cause the environmental defense mechanism To overcome these changes, evolutionunable to follow us.


sixth mass extinction

This is the main conclusion of a study on the Aarhus University (Denmark) and the University of Gothenburg (Sweden), recently published in “Proceedings of the National Academy of Sciences” (PNAS), which indicates that this will be the cause of the extinction of many species of mammals during the next five decades if current conservation efforts do not improve.

At this rate, and after only 50 years, nature would need between 3 to 5 million years to return to current levels (where in the last five centuries 322 species of vertebrates have disappeared) and of 5 to 7 million years to restore biodiversity before the emergence of Homo sapiens.

The researchers used an extensive database of mammals, which includes not only the species that still exist, but also the hundreds of species that lived in the recent past and became extinct when humans spread across the world, like mammoths or saber-toothed tigers. .

“The large mammalsThat is megafauna, such as giant sloths and saber-toothed tigers, which died out around 10,000 years ago, were evolutionarily very different. As they had few close relatives, their extinctions meant that entire branches of Earth’s evolutionary tree were severed.” it is said Matt Davis, paleontologist at Aarhus University, who led the study.

And adds: “There are hundreds of species of shrews, so they can withstand some extinctions. There were only four species of saber-toothed tigers and they are all dead.

Species now threatened

But beyond the species that have become extinct, there are now many types of animals that are threatened. For example, he black rhino it is very likely to disappear in the next 50 years. Or the asian elephantone of only two surviving species descended from species as large as mammoths and mastodons, has less than a 33% chance of surviving this century.

The researchers therefore also wondered whether existing mammals could naturally regenerate lost biodiversity and how long the process would take.

In the best-case scenario, where humans have stopped destroying habitats and eradicating species, it will take 3-5 million years for mammals to diversify enough to regenerate the branches of the evolutionary tree they are expected to lose in the next 50 years. .

But it will take more than 5 million years to regenerate what was lost by giant Ice Age species, where the world was populated by giant beavers, giant armadillos or giant deeramong others.

Giant mammals: a past that will never come back

“Although we once lived in a world of giants, we now live in a world increasingly depleted of large wild mammal species. The few remaining giants, such as rhinos and elephants, are in danger of extinction.” alert the teacher Jens-Christian Svenningfrom Aarhus University, which runs an extensive megafauna research program included in the study.

However, there is something positive to take away: all this data could be used to quickly identify species in danger of extinction and with a different evolutionso that conservation efforts can be prioritized and focused on preventing the most severe extinctions. “Now it is much easier to save biodiversity than to evolve it again later,” Davis concludes.

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