Branches of the ‘tree of life’ are being extinct, says study – 09/19/2023 – Environment

Human beings are causing the loss of entire branches of the “tree of life”, according to a scientific study published this Monday (18). The research warns of the threat of a sixth mass extinction.

“The extinction crisis is as serious as that of climate change”, emphasized Gerardo Ceballos, professor at Unam (National Autonomous University of Mexico) and co-author of the research published in the journal Proceedings of the National Academy of Sciences (PNAS). ).

“What is at stake is the future of humanity,” he said.

The study not only analyzes the loss of a species, but the extinction of entire genera. In the classification of living beings, the genus is located between the range of species and family. For example, dogs are a species belonging to the genus Kennelswhich, in turn, belongs to the canid family.

“It’s a really significant contribution, I think it’s the first time anyone has tried to evaluate modern extinction rates at a level higher than that of species,” said Robert Cowie, a biologist at the University of Hawaii (USA), who was not involved in the study.

Therefore, “it actually demonstrates the loss of entire branches of the ‘tree of life'”, a famous representation of living beings initially developed by Charles Darwin.

For Anthony Barnosky, professor emeritus at the University of California at Berkeley, the analysis shows that “not only are we just trimming terminal branches, but using a chainsaw to get rid of big arms.”

73 extinct genera

The researchers were mainly based on species considered extinct by the International Union for Conservation of Nature (IUCN). They focused on vertebrates (excluding fish), for which more data are available.

Of the nearly 5,400 genera (comprising 34,600 species), they concluded that 73 became extinct in the last 500 years, the majority in the last 200 years. Scientists then compared this number to the extinction rate estimated from existing fossil records.

“Based on the extinction rate in the previous millions of years, we expected to lose two genera. But we lost 73,” Ceballos explained.

The study calculates that these losses should have occurred over 18,000 years, not 500, although estimates remain uncertain since not all species are known and the fossil record is incomplete.

The loss of these genera is associated with human activities such as the destruction of habitats for agriculture or construction of infrastructure, as well as predatory fishing, hunting, among others.

This puts the entire ecosystem at risk, warns Ceballos. “Our concern is that we are losing things so fast that, to us, this is a sign of the collapse of civilization,” he said.

Time to act

All the experts interviewed by the report agreed that the current rate of extinction is alarming, but they continue to debate whether this situation represents the beginning of a sixth mass extinction — the last corresponds to the one generated by the asteroid that exterminated the dinosaurs, 66 million years ago.

Broadly speaking, scientists define a mass extinction as the loss of 75% of species in a short period of time. Using this “arbitrary” definition, Cowie said, a new one has not yet been produced.

However, if we assume that “species will continue to go extinct at the current rate, then this will happen”, he warned, extolling that “this is the beginning of a potential sixth mass extinction”.

But, for him, there is still time to save many genres. To achieve this, it is necessary to stop the destruction of natural habitats and restore those that have been lost, he highlighted.