Life on Earth is diverse and complex, with millions of species belonging to different groups that share common ancestors and characteristics.
These groups are organized into a hierarchical system called the Tree of life, which represents the evolutionary history and relationships of all living organisms.
However, this tree of life is under threat from human activities that are causing a rapid and unprecedented loss of biodiversity.
A new study has revealed that human-driven mass extinction is not only wiping out individual species but also entire branches of the tree of life, reducing the diversity and complexity of life on Earth.
This article will summarize the main findings and implications of this study, which was published in the Proceedings of the National Academy of Sciences.
The sixth mass extinction
LUIS TATO/AFP via Getty Images
The Earth has experienced five major mass extinctions in its history, each one wiping out a large proportion of the planet's biodiversity.
The most recent one, the Cretaceous-Paleogene event, occurred 66 million years ago and killed off the dinosaurs and many other species.
Now, many scientists believe that we are in the midst of the sixth mass extinction, caused by human activities such as habitat destruction, overexploitation, pollution, climate change, and invasive species.
Unlike previous mass extinctions, which were driven by natural factors such as asteroid impacts or volcanic eruptions, the current one is entirely anthropogenic, meaning that it is caused by humans. This makes it unique and unprecedented in the history of life on Earth.
Moreover, the rate and magnitude of the current mass extinction are much higher than those of the past ones.
According to a recent study by Stanford University and the National Autonomous University of Mexico, published in the Proceedings of the National Academy of Sciences, human actions are wiping out vertebrate animal species hundreds of times faster than they would otherwise disappear.
A genus is a higher category into which taxonomists sort species that share common characteristics and evolutionary origins.
For example, the genus Homo includes humans and several extinct relatives, such as Neanderthals and Homo erectus.
The study found that 73 genera of land-dwelling vertebrates have gone extinct since 1500 AD, with birds suffering the heaviest losses with 44 genus extinctions, followed in order by mammals, amphibians, and reptiles.
Some of the well-known examples of extinct genera include the passenger pigeon (Ectopistes), the Tasmanian tiger (Thylacinus), and the Yangtze river dolphin (Lipotes).
Each of these species was also the last member of its genus, meaning that they represented an entire branch of the tree of life that was cut off by human-driven mass extinction.
The study calls this phenomenon a "mutilation of the tree of life", as it reduces the diversity and complexity of life on Earth.
The study also compared the current rate of vertebrate genus extinction with that of the last million years, based on the fossil record of mammals.
It found that the current rate exceeds that of the last million years by 35 times.
This means that, without human influence, Earth would likely have lost only two genera during that time.
In five centuries, human actions have triggered a surge of genus extinctions that would otherwise have taken 18,000 years to accumulate. This is what the study calls a "biological annihilation".
The implications for humanity and nature
The loss of entire genera has serious implications for both humanity and nature. As Ceballos and Ehrlich point out, "What we're losing are our only known living companions in the entire universe".
Each genus represents a unique evolutionary history and a potential source of scientific knowledge and biotechnological innovation.
For example, some extinct genera had remarkable adaptations to their environments, such as echolocation in bats or electroreception in sharks. These traits could inspire new inventions or solutions to human problems.
Moreover, each genus plays a role in maintaining the functioning and stability of ecosystems, which provide essential services to humanity such as food production, water purification, climate regulation, pollination, pest control, and recreation.
For example, some extinct genera were important seed dispersers or predators that influenced the structure and composition of plant communities.
Their disappearance could have cascading effects on other species and processes in their habitats.
The study warns that if human-driven mass extinction continues at its current pace, it could lead to a collapse of civilization and a deterioration of human well-being.
The authors urge immediate action to halt and reverse the loss of biodiversity, such as expanding protected areas, restoring degraded habitats, reducing consumption and waste, promoting sustainable agriculture and energy sources, and enhancing environmental education and awareness.
The study concludes that "the survival of humanity depends on preserving biodiversity". Therefore, we must respect and protect all forms of life on Earth before it is too late.
