Human action is destroying entire branches of the tree of life

2023-09-19 13:50:04

The passenger pigeon, the Tasmanian tiger, the baiji or Yangtze River dolphin are some of the recent victims of what many scientists have declared as the sixth mass extinction; this time, produced by man.

To the consensus that the human action is destroying vertebrate species at a much faster rate than they would otherwise disappear, adds 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 deeper, since, until now, the emphasis was mainly on the extinctions of species. This investigation verifies, however, that some of the most recent disappearances were also the last member of its genusthe highest category into which taxonomists classify species.

The current rate of extinction of vertebrate genera is 35 times that of the last million years, according to the study

Gerardo Ceballosprincipal researcher at the UNAM Institute of Ecology, and Paul Ehrlichprofessor emeritus of population studies in the Stanford School of Humanities and Sciences, have found that entire branches are being lost in what they call a “mutilation of the tree of Life”.

The current rate of extinction of genera of vertebrates exceeds 35 times that of the last million years, according to the study. At the rate of wildlife annihilation over the past five centuries, the human influence on the current environmental crisis is undeniable.

When asked by SINC, researcher Gerardo Ceballos assures that using the notion of the “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 the evolutionary relationship of living beingsthat is, on the tree of life, the position of branches indicates how close the relationship of a species or genus is with others.”

On the other hand, “the thickness and position of the branches “They determine the impact that the extinction of genera or species has on the evolution of life on Earth, as well as on the well-being of humans,” 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 the extinction of genera is causing a severe impact on the biological Diversity of the planet,” he emphasizes.

As Ceballos describes, “in the long term, we are opening a big gap in the evolution of existence on the planet.” But, also, “in this century, what we are doing to the tree of life will cause a lot suffering to 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 annihilation

Thanks to the information on the conservation status of the species prepared by the International Union for Conservation of Nature (IUCN) and Birdlife International, among other reliable lists and databases, the authors have been able assess extinction at the genus level.

From these sources, the authors They examined 5,400 genres of animals terrestrial vertebrateswhich include 34,600 species. As outlined in the work, since the 16th century they have disappeared 73 genres of this group of animals. The birds suffered the greatest losses, with 44 genus extinctions, followed by mammals; then, amphibians and reptiles.

The article focuses on the trend or magnitude of the loss, Ceballos confirms: “The extinctions of millions of years ago are called normal extinctions or background extinctions. “In the study we indicated that, for example, birds suffered an extinction rate 50 times higher in recent times than what occurred during the last million years.”

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

The genera that became extinct in the last five centuries “should have disappeared in 26,100 years,” which means that “in the Anthropocene, extinctions have accelerated in a truly alarming way,” he says.

In other words, in five centuriesthe human action has triggered a wave of extinctions of genres that would otherwise have taken thousands of years to accumulate. This phenomenon is what the article calls a “biological annihilation.”

Extinctions of genera affect more than those of species: when a species disappears, others of its genus can play part of their role in the ecosystem

“As scientists, we have to be careful not to be alarmist,” acknowledges Ceballos. However, the “seriousness of the findings,” in this case, requires stronger language than usual, as he admits. “It would be unethical to fail to explain the magnitude of the problem, since we ourselves, as well as other researchers, are alarmed,” he confesses.

Losses for which words are missing

At many levels, genus extinctions affect more than species extinctions. When a species disappears, the expert explains, other species of its genus can play at least part of its role in the ecosystem. And since these species retain a portion of the genetic material of their extinct cousins, they also maintain some of their evolutionary potential.

As on the tree of life, if a single “twig” (a species) falls, others nearby can branch out relatively quickly, filling the gap, as the original would have done. In that case, the planet’s species diversity 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.

But when entire “branches” (genera) fall, a huge hole is left in the plant cover, a loss of biodiversity that can take tens of millions of years to “regrow,” through the evolutionary process of speciation.

According to Ceballos, humanity cannot wait that long for its health to recover. life support systemsgiven that the stability of our civilization depends, to a large extent, on the services provided by the Earth’s biodiversity.

“Las wild plants and animalsintegrated into ecosystemsthey provide those environmental services”, he specifies. To illustrate the value that these have, the expert equates them with “benefits such as the adequate combination of gases in the atmosphere to make the Earth habitable, the pollination of 70% of the crops we use, and countless products such as wood , essences, forage, honey, etc. Hence, “every time we lose a gender, we are losing the planet’s capacity to maintain 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 repercussions on the history of life on Earth, on the future of evolution and on our well-being, which depends on the proper functioning of the nature”.

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

Gerardo Ceballos (UNAM)

However, the term “wellbeing” seems insufficient to warn about the impact on human health that the disappearance of a single animal genus can have. For example, when the increasing prevalence of Lyme disease is noted, because white-footed mice—the main carriers 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, human cases of this ailment.

But, in addition to the proportional explosion of disasters for humanitymass extinction also entails an irreparable loss of knowledge. Ceballos and Ehrlich point to the gastric brooding frog, also the last member of an extinct genus, as a missed opportunity to continue investigating stomach diseases. It turns out that those female frogs swallowed their own fertilized eggs and raised tadpoles in their stomachs, while deactivating stomach acid.

All this without counting on the worsening climate crisis: “Climate alteration is accelerating extinction, and extinction is interacting with the climatebecause the nature of the plants, animals and microbes on the planet constitutes one of the great determinants of the type of climate we have,” warns Ehrlich.

A crucial answer, and still absent

For his part, Ceballos emphasizes the impact that “these extinctions have and can have in the civilization”. These losses, “in combination with climate change and other environmental problems,” can lead to “a collapse of civilization in the coming decades,” in his own words.

To avoid new extinctions and the resulting social crises, Ceballos and Ehrlich call for a immediate political, economic and social actionon unprecedented scales.

The priority of the effort should be, in his opinion, the tropicssince tropical regions have the highest concentration of both genus extinctions and genera with only one species remaining.

“The size and increase of the human population, the increasing scale of its consumption and the fact that consumption is very unequal “are important parts of the problem,” in the opinion of the authors.

However, Ceballos declares that “we still have time to avoid the most severe impacts of the extinction of biodiversity.” Although, “the window of opportunity is small and closing rapidly, what we do in the next two decades will determine the future of biodiversity and civilization,” he concludes.