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Sixth mass extinction is wiping out entire branches of Earth's tree of life

The sixth mass extinction, primarily driven by human activities, is more dire than previously anticipated. Not only are we seeing a rapid extinction of species, but entire branches on the tree of life are now disappearing.

Researchers from Stanford University and the National Autonomous University of Mexico have recently revealed these alarming findings in a study published in the journal Proceedings of the National Academy of Sciences

Tree of life is vanishing

While the extinction of species like the passenger pigeon and the Yangtze river dolphin is deeply concerning, the loss is more profound. 

Each of these species was the last of its genus, marking an entire branch of life’s tree wiped out.

Lead researchers, Gerardo Ceballos and Paul Ehrlich, assessed 5,400 genera of terrestrial vertebrates, including 34,600 species. 

Their results were staggering: 73 genera have become extinct since 1500 AD. 

Genus extinctions 

Birds were hardest hit with 44 genus extinctions, trailed by mammals, amphibians, and reptiles. This rate of extinction surpasses the last million years by 35 times. 

In other words, without human influence, in just five centuries, human actions have triggered a surge of genus extinctions that would have otherwise taken 18,000 years. The researchers refer to this as a “biological annihilation.”

“In the long term, we’re putting a big dent in the evolution of life on the planet,” said Ceballos. “But also, in this century, what we’re doing to the tree of life will cause a lot of suffering for humanity.”

“What we’re losing are our only known living companions in the entire universe,” added Ehrlich..

Alarming repercussions 

When a species vanishes, others within its genus can potentially compensate for its ecological function. 

However, the extinction of an entire genus creates an irreparable gap in the ecosystem that could require tens of millions of years to restore through natural evolution. 

This imbalance impacts humanity significantly. For example, the eradication of passenger pigeons, a control on the population of white-footed mice (primary carriers of Lyme disease), has led to a surge in Lyme disease cases among humans.

“As scientists, we have to be careful not to be alarmist,” said Ceballos. But, he explained, the gravity of the findings in this case called for more powerful language than usual. “We would be unethical not to explain the magnitude of the problem, since we and other scientists are alarmed.”

Further implications

The loss of genera means losing invaluable knowledge. The gastric brooding frog, now extinct and the last of its genus, could have offered insights into human diseases like acid reflux.

Loss of genera could also exacerbate the worsening climate crisis. “Climate disruption is accelerating extinction, and extinction is interacting with the climate, because the nature of the plants, animals, and microbes on the planet is one of the big determinants of what kind of climate we have,” said Ehrlich.

Extinction crisis and the tree of life

To prevent further extinctions, the researchers are calling for immediate political, economic, and social action on unprecedented scales.

Increased conservation efforts should prioritize the tropics. This is due to the fact that the tropical regions have the highest concentration of both genus extinctions and genera with only one remaining species. The experts are also calling for increased public awareness of the extinction crisis, especially given how deeply it intersects with the more-publicized climate crisis.

“The size and growth of the human population, the increasing scale of its consumption, and the fact that the consumption is very inequitable are all major parts of the problem,” said the researchers.

“The idea that you can continue those things and save biodiversity is insane,” Ehrlich added. “It’s like sitting on a limb and sawing it off at the same time.”

More about the sixth mass extinction

Throughout Earth’s vast history, five significant mass extinctions have punctuated the otherwise slow and methodical evolution of life. These catastrophic events have wiped out between 50% to more than 90% of Earth’s species, reshaping the trajectory of evolution each time.

Today, we are on the precipice of what scientists have dubbed the “Sixth Mass Extinction,” a widespread decline in species predominantly driven by human activities. Unlike previous extinctions caused by natural cataclysms, humans are responsible. This new wave of biodiversity loss is emblematic of the Anthropocene epoch – a proposed epoch that emphasizes the significant and enduring impact humans have on our planet.

Causes and consequences

Human-driven causes

  1. Habitat Destruction: The expansion of agriculture, infrastructure, and urbanization have led to significant habitat loss and fragmentation, making it difficult or impossible for many species to survive.
  2. Overexploitation: Overfishing, hunting, and poaching have led to rapid declines in many species.
  3. Pollution: From plastics choking marine life to chemicals contaminating water sources, pollution poses a direct threat to biodiversity.
  4. Climate Change: Rising temperatures, ocean acidification, and extreme weather events disrupt habitats and stress ecosystems.
  5. Invasive Species: The movement of species to new areas, often due to human actions, can lead to the decline or extinction of native species.


  1. Loss of Biodiversity: Species extinctions lead to the degradation of ecosystems, which can result in decreased ecosystem resilience and functionality.
  2. Disruption of Food Webs: As key species go extinct, the effects cascade throughout the ecosystem, affecting predator-prey dynamics and resource availability.
  3. Economic Impact: Biodiversity loss can affect industries like agriculture, pharmaceuticals, and tourism.
  4. Loss of Ecosystem Services: Clean water, pollination of crops, and disease control are some services that are compromised with decreasing biodiversity.

Responding to the crisis

To mitigate the effects of the sixth mass extinction, comprehensive and immediate action is required. Some steps include:

  1. Protected Areas: Expanding and connecting protected areas can provide refuges for species and preserve vital habitats.
  2. Sustainable Development: Balancing human needs with the conservation of the natural world is crucial. This involves sustainable farming, fishing, and forestry practices.
  3. Public Awareness: Educating the public about the importance of biodiversity can foster a culture of conservation.
  4. Legislation and Global Agreements: International cooperation, backed by effective policies and regulations, can drive large-scale conservation efforts.

The sixth mass extinction, unlike its predecessors, is a testament to humanity’s profound influence on the planet. It serves as a dire reminder of the interconnectedness of life and the responsibility we bear as stewards of the Earth.

Addressing the crisis demands collective global action, informed decisions, and a commitment to preserving the intricate web of life for future generations.

The study is published in the journal Proceedings of the National Academy of Sciences.

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