Human actions destroy entire branches of the tree of life

The passenger pigeon, the Tasmanian tiger, the baiji and the Yangtze dolphin are some of the latest victims of what many scientists have called the sixth mass extinction; This time produced by humans.

To the consensus that the human action is destroying vertebrate species much faster than they would otherwise disappear, add the results of an analysis by Stanford University (USA) and the National Autonomous University of Mexico (UNAM), published this week in Proceedings of the National Academy of Sciences.

The work shows that the crisis may be even more serious, as most of the focus so far has been on animal extinctions species. However, this investigation confirms that some of the recent disappearances also involved individuals last member of its genusthe highest category into which taxonomists classify species.

According to the study, the current extinction rate of vertebrate species is 35 times higher than in the last million years

Gerardo CeballosPrincipal Investigator at the UNAM Institute of Ecology, and Paul EhrlichProfessor Emeritus of Population Studies at the Stanford School of Humanities and Sciences, have found that entire branches in a so-called “mutilation of tree of Life“.

The current extinction rate of the genera of Vertebrates exceeds 35 times that of the last million years, according to the study. Given the rate at which wildlife has been wiped out over the last five centuries, the human impact on the current environmental crisis is undeniable.

When asked by SINC, researcher Gerardo Ceballos assures that using the term “tree of life”, as Charles Darwin called it, is a simple way to understand the “complexity” of life.

“The Tree of Life basically means two things,” he continues; The first is this evolutionary relationship of living thingsthat is, at the tree of life, the Location of branches indicates how closely related a species or genus is to others.”

On the other hand, “the thickness and position of the branches “They determine what impact the extinction of genera or species has on the development of life on Earth and on human well-being,” he explains.

What we are losing are our only known living companions in the entire universe

Paul Ehrlich (Stanford)

“Using the tree of life in this study allows us to visualize that species extinctions have serious implications for humanity Biological Diversity of the planet,” he emphasizes.

As Ceballos describes: “In the long term, we are opening up a big gap in the evolution existence on the planet.” But also “in this century, what we are doing to the tree of life will have a big impact.” suffering for humanity“.

For his part, Ehrlich, who is also an emeritus member of the Stanford Woods Institute for the Environment, adds: “What we are losing is our only living companions known throughout the universe.”

biological destruction

The authors were able to do this thanks to information on the conservation status of species compiled by the International Union for Conservation of Nature (IUCN) and Birdlife International, as well as other reliable lists and databases Assessing extinction at the genus level.

The authors come from these sources They examined 5,400 genres of animals Land vertebrateswhich include 34,600 species. As stated in the work, they have disappeared since the 16th century 73 genres this group of animals. The Birds suffered the greatest losses, with 44 extinct genera, followed by mammals; then amphibians and reptiles.

The article focuses on the trend or size Ceballos confirms the loss: “The extinction that occurred millions of years ago is called a normal extinction.” background death. “In the study, we pointed out that birds, for example, have recently suffered an extinction rate 50 times higher than in the last million years.”

If one had followed the historical trend, “one genus of birds would be expected to have become extinct in the last 500 years; However, 44 genes were lost,” he argues.

The genera that went extinct in the last five centuries “should have disappeared in 26,100 years,” meaning that “extinctions have increased in a really alarming way in the Anthropocene,” he says.

In other words, in five centuriesThe human action triggered one wave of extinction of genres that would otherwise have taken thousands of years to emerge. This phenomenon is referred to in the article as “biological annihilation.”

The extinction of genera affects more than the extinction of species: when a species disappears, others in its genus may take over some of its role in the ecosystem

“As scientists, we have to be careful not to sound the alarm,” admits Ceballos. However, the “seriousness of the results” in this case requires stronger language than usual, he admits. “It would be unethical not to explain the extent of the problem, as we ourselves and other researchers are alarmed,” he admits.

Losses for which there are no words

On many levels, the extinction of genera has a greater impact than the extinction of species. If a species disappears, the expert explains, other species in its genus can take over at least part of its role in the ecosystem. And because these species retain some of the genetic material of their extinct relatives, they also retain some of their evolutionary potential.

As with the Tree of Life, when a single “branch” (species) falls, others nearby can branch out relatively quickly and fill the gap, as would have been the case with the original. In this case, the planet’s biodiversity remains more or less stable.

Two specimens of the Tasmanian tiger (or thylacine), photographed in 1902. This animal was the last living member of its genus. / Source: Smithsonian Institution / CC Wikipedia.

However, when entire “branches” (genera) fall off, a huge hole is created in the plant cover, a loss of biodiversity that can take several million years to “grow back” through the evolutionary process of speciation.

According to Ceballos, humanity cannot wait that long for its health to recover. Life support systemssince the stability of our civilization depends to a large extent on the achievements of the Earth’s biological diversity.

“The wild plants and animalsintegrated into Ecosystemsthey provide these Environmental Services“, he specifies. To illustrate the value that these have, the expert puts them with “benefits such as the appropriate combination of gases in the atmosphere to make the Earth habitable, the pollination of 70% of the plants we use and countless products such as wood, Essences,” food, honey, etc. Therefore, “every time we lose a gender, we lose the planet’s ability to sustain life in general and human well-being in particular,” he clarifies.

Consequences of an evolutionary gap

The author calls for understanding that “the disappearance of a species or genus of plants or animals has implications for the history of life on Earth, for the future of evolution and for our well-being, which depends on the proper functioning of nature.”

The disappearance of a species or genus of plants or animals has implications for the history of life on Earth, for the future of evolution, and for our well-being.

Gerardo Ceballos (UNAM)

However, the term “well-being” does not seem to be sufficient to warn against this Effects on human health that can result in the disappearance of a single species of animal. For example, when the increasing prevalence of Lyme disease is noted because white-footed mice – the main vectors of the disease – used to compete with passenger pigeons for food such as acorns. With the disappearance of these birds and the decline of predators such as wolves and pumas, mouse populations have skyrocketed, and with them the number of cases of the disease in humans.

But in addition to the proportional explosion of Disasters for humanityMass extinction also brings with it an irreparable result Loss of knowledge. Ceballos and Ehrlich point this out Stomach brooding frog, also the last member of an extinct genus, as a missed opportunity to further research stomach diseases. It turns out that these female frogs swallowed their own fertilized eggs and raised tadpoles in their stomachs, all while deactivating stomach acid.

All this without counting on it worsening climate crisis: “Climate change is accelerating extinction, and Extinction interacts with climateBecause the nature of the plants, animals and microbes on the planet is one of the major determinants of our climate,” warns Ehrlich.

A crucial answer that is still missing

For his part, Ceballos emphasizes the Effects that “this extinction has and can have taken place in the….” civilization“. These losses, “combined with climate change and other environmental problems,” could, in his own words, lead to “a collapse of civilization in the coming decades.”

In order to avoid new species extinctions and the resulting social crises, Ceballos and Ehrlich are calling for one immediate political, economic and social actionon an unprecedented scale.

The priority of efforts, in his opinion, should be Tropicsas tropical regions have the highest concentration of extinct genera and genera and only one species remains.

“The size and growth of the human population, the increasing extent of its consumption and the fact that consumption is very unequal “are important parts of the problem,” say the authors.

However, Ceballos explains that “we still have time to avoid the most serious consequences of biodiversity extinction.” Although the Window of opportunity Because climate change is small and closing rapidly, what we do in the next two decades will determine the future of biodiversity and civilization,” he concludes.

Ceballos, G. et al. “Mutilation of the tree of life through mass extinction of animal species.” Proceedings of the National Academy of Sciences (2023)

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