Friday, September 29, 2023

Scientists warn of threat of sixth mass extinction

But there is “urgency”, because what is at stake is “the future of humanity”, he told AFP.

There are already numerous studies on the disappearance of species, but the specificity of this one is that it has analyzed the extinction of entire genera.

In the classification of living beings, the genus is situated between the range of species and family. For example, the dog is a species belonging to the genus Canis, in turn belonging to the family Canidae.

“I think this is the first time we’ve tried to evaluate the extinction rate at a higher level than the species,” Robert Cowie, a biologist at the University of Hawaii who was not involved in the study, told AFP. “This demonstrates the loss of entire branches of the tree of life,” a representation of life first developed by Charles Darwin.

The study shows that “we’re not just cutting off twigs, we’re using a chainsaw to get rid of the big branches,” added Anthony Barnosky, professor emeritus at the University of California, Berkeley.

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73 extinct genera

The researchers relied in particular on the lists of extinct species from the International Union for Conservation of Nature (IUCN). They focused on vertebrate species (excluding fish), for which more data is available.

Of some 5,400 genera (comprising 34,600 species), they concluded that 73 of them had become extinct in the last 500 years, most in the last two centuries. First of all, birds, followed by mammals, amphibians and reptiles.

To understand whether this rate is higher than normal, the researchers compared this result with the extinction rate estimated using very long-term trace fossils.

“Based on the extinction rate over the last few million years, you would expect two genera to go extinct, but we lost 73,” said Gerardo Ceballos.

According to the study, the extinction of these 73 genera should have taken 18,000 years, not 500.

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These estimates remain uncertain, many species are not even known and the fossil records are incomplete. But, according to the researcher, they are probably underestimated.

The cause of these extinctions? Human activities, which destroy habitats for crops, infrastructure and other needs, but also overexploitation (overfishing, hunting, animal trafficking, etc.).

However, the loss of a genus can have consequences on the functioning of an entire ecosystem. With a possible “collapse of civilization” in the long term, argues Gerardo Ceballos.

“If you have a wall made of bricks, and each brick is one type, removing a brick is not going to cause the wall to collapse,” he compares. “But if you remove too many more, then the wall falls.”

The five great mass extinctions ©Our world in data

“There is still time” to act

According to him, there is no doubt that this is the sixth mass extinction. However, it remains a matter of debate whether it has already begun, although all experts agree that the current rate of extinction is alarming.

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The last mass extinction was 66 million years ago, when an asteroid impact caused the disappearance of the dinosaurs.

“An arbitrary value of 75% of species lost in a short period of time is widely used to define a mass extinction,” explains Robert Cowie. According to this threshold, the sixth mass extinction “has not yet occurred.”

But if “species continue to become extinct at the current rate (or faster), then this will happen,” he says. “We can say that we are at the beginning of a possible sixth mass extinction.”

Its particularity? Which is triggered by a species, the human, also having the power to remedy it.

“The window for action is closing quickly,” warns Gerardo Ceballos, “but we still have time to save many genres.”

The priority is to stop the destruction of natural habitats and restore those lost, insists the researcher, who hopes for rapid awareness: “Governments, companies and people need to know what is happening and what the consequences are.”

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