The Three Types of Extinction: Natural, Mass, and Human-Driven

Species extinction is not a new phenomenon. Life on Earth has always involved the disappearance of some species and the emergence of others. But what we’re witnessing today is fundamentally different from what nature intended. Current extinction rates are estimated to be 1,000 times higher than natural background rates, and future rates are likely to be 10,000 times higher. Understanding the three types of extinction – natural, mass, and human-driven – is essential to grasping the scale of the biodiversity crisis unfolding around us.

Natural extinction: the slow rhythm of life and death 🔗

Extinction, in its most basic sense, is a natural process. Species evolve, thrive, and eventually fade away as their environment changes over millions of years. This steady, slow loss of species over geological time is known as the background extinction rate.

Scientists measure this rate in several ways. For instance, at the background rate, one bird species is expected to go extinct roughly every 400 years. Another way to look at it: if you tracked a million species over time, you would expect to observe roughly 0.1 to 1 extinction per year under normal conditions.

Different groups of organisms have different natural lifespans before they go extinct. Invertebrates typically last about 11 million years, mammals around 1 million years, and marine animals about 4 to 5 million years. These figures come from fossil records and give scientists a baseline for understanding what “normal” species turnover looks like.

Natural extinction typically happens because of gradual environmental shifts, competition with other species, or evolutionary failure to adapt to slow changes in habitat or climate. Many past extinctions were caused by gradual environmental shifts, evolutionary competition, or local interspecific dynamics. It is, in essence, evolution’s pruning mechanism – clearing space for new species to arise and fill ecological roles.

The key word here is gradual. Natural extinction unfolds over thousands to millions of years, giving ecosystems time to adjust. New species step in to fill the roles left behind, and the overall balance of life remains intact.

Mass extinction events: when catastrophe reshuffles life 🔗

While natural extinction is a quiet, steady process, mass extinction is something else entirely. A mass extinction occurs when a large percentage of Earth’s species disappear in a geologically short period – typically defined as the loss of about 75% or more of species in under 2.8 million years.

There have been five major mass extinction events in Earth’s history over the past 500 million years, collectively known as the “Big Five.” Each of these events dramatically reshaped life on the planet.

The Big Five mass extinctions 🔗

1. End-Ordovician (about 443 million years ago): This was the first major mass extinction event, wiping out roughly 85% of all species. Scientists believe it was triggered by plummeting temperatures and massive glaciation, which caused dramatic drops in sea level.

2. Late Devonian (about 372 million years ago): Despite eliminating around 70% of all marine species, this event was one of the least severe among the Big Five. It unfolded gradually over millions of years, likely driven by ocean oxygen depletion.

3. End-Permian (about 252 million years ago): Known as the “Great Dying,” this was the deadliest extinction in Earth’s history. Roughly 96% of all marine species and about three out of every four land species perished. The primary culprits were massive volcanic eruptions in Siberia, which poisoned the atmosphere and acidified the oceans. It took a staggering 30 million years for vertebrate life to fully recover.

4. End-Triassic (about 200 million years ago): This event eliminated about 80% of Earth’s species, probably caused by intense volcanic activity that raised carbon dioxide levels, global temperatures, and ocean acidification.

5. End-Cretaceous (about 66 million years ago): The most famous of the Big Five, this is the event that ended the reign of the dinosaurs. An asteroid roughly 10 kilometres wide struck Earth near what is now the Yucatán Peninsula in Mexico. The impact sent massive waves of heat, dust, and soot around the planet, blocking sunlight and collapsing ecosystems.

All of the Big Five were caused by some combination of rapid, dramatic changes in climate along with significant shifts in the composition of land and ocean environments. Whether it was volcanic eruptions releasing toxic gases, asteroid impacts blocking sunlight, or glaciation freezing over the seas, each event pushed the planet’s biodiversity past a breaking point.

But here’s a crucial detail: after each mass extinction, life recovered. It took millions of years, but new species evolved to fill the vacated ecological roles. For example, the extinction of non-avian dinosaurs cleared the way for mammals to rise and eventually dominate the land.

Anthropogenic extinction: the human fingerprint on biodiversity loss 🔗

We now come to the third and most urgent type of extinction – anthropogenic (human-caused) extinction. Unlike natural extinction, which takes millions of years, and mass extinctions, which are triggered by catastrophic natural events, anthropogenic extinction is driven by the everyday activities of a single species: us.

According to the landmark 2019 IPBES Global Assessment, around 1 million animal and plant species are now threatened with extinction, many within decades – more than ever before in human history. The report, compiled by 145 experts from 50 countries, paints an alarming picture of how human activity is unravelling the web of life at a pace never seen before.

The main drivers of human-caused extinction 🔗

According to the IPBES, the main direct threats to biodiversity, in order of importance, are: land and sea use change, direct exploitation, pollution, invasive alien species, and climate change.

Habitat destruction and land use change is by far the biggest driver. When forests are cleared for agriculture, wetlands are drained for development, or oceans are trawled to exhaustion, the species that depend on those habitats lose their homes. The E.O. Wilson Biodiversity Foundation identifies habitat loss as the single greatest threat to species worldwide.

Overexploitation – including overfishing, poaching, and the illegal wildlife trade – directly removes species from their environments faster than they can reproduce. Pollution from industrial chemicals, agricultural runoff, and plastics contaminates habitats and poisons wildlife. Invasive species, introduced by human trade and travel, outcompete and prey upon native species. And climate change, driven by greenhouse gas emissions, is altering habitats and weather patterns faster than many species can adapt.

The IPBES report noted that the average abundance of native species in most major land-based habitats has fallen by at least 20%, mostly since 1900. More than 40% of amphibian species, nearly 33% of reef-forming corals, and over a third of all marine mammals are currently threatened.

How fast are we losing species? 🔗

The numbers are sobering. In the case of vertebrates alone, scientists expected about nine species to go extinct over the 20th century at background rates. In reality, 390 vertebrate species disappeared since 1900 – more than 40 times the natural rate.

A study published in Science Advances compared observed vertebrate extinctions over the past 114 years against background rates. What would have taken 2,000 to 10,000 years under normal conditions has happened in just over a century. This acceleration is why many scientists argue we have entered a sixth mass extinction – one driven not by asteroids or volcanoes, but by human actions.

Why extinction is irreversible – and why it matters 🔗

When a species goes extinct, it doesn’t just vanish as a name on a list. It takes with it millions of years of unique evolutionary history, a distinct genetic makeup, and a specific role within its ecosystem. Extinction is permanent. There is no bringing back a species once it is gone.

Every species plays a role in its ecosystem – as a pollinator, a predator, a decomposer, a seed disperser. When one species disappears, the effects ripple outward. Predators lose prey. Plants lose pollinators. Soil loses the organisms that keep it fertile. These cascading effects can destabilise entire ecosystems, sometimes in ways that are difficult to predict.

As researchers at Science Advances noted, the loss of biodiversity affects human well-being by disrupting crucial ecosystem services such as crop pollination and water purification, and by destroying the culturally and scientifically important living world around us.

The economic implications are also significant. Ecosystems provide “services” – clean water, air purification, flood control, pollination of food crops – that underpin human economies and survival. As the United Nations Foundation noted, the loss of clean air, drinkable water, pollinating insects, and forests poses as serious a threat to human survival as climate change itself.

There is also the loss of potential. Many modern medicines originate from compounds found in plants and animals. Each species that goes extinct takes with it potential cures, materials, and biological insights we may never discover.

The urgency of conservation efforts 🔗

Given the scale and speed of the current extinction crisis, conservation has never been more important. But the good news is that conservation works when it is properly funded and implemented.

The IPBES assessment found that the extinction risk of birds, mammals, and amphibians would have been at least 20% greater without conservation actions taken in recent decades. Protected areas, captive breeding programs, anti-poaching laws, and habitat restoration projects have pulled numerous species back from the brink.

Several key strategies are essential going forward:

Protecting and restoring habitats remains the single most effective way to prevent extinctions. Expanding protected areas on land and at sea gives species the space they need to survive and recover.

Tackling climate change is inseparable from biodiversity conservation. Healthy ecosystems naturally absorb carbon from the atmosphere, making biodiversity protection one of our most effective climate solutions.

Strengthening legal protections through international agreements like the Convention on Biological Diversity and national wildlife laws is vital for holding governments and industries accountable.

Monitoring and research through tools like the IUCN Red List help scientists track which species are most at risk and where conservation resources are most needed. The Red List has now assessed over 172,600 species and serves as the world’s most comprehensive source on global extinction risk.

Addressing root causes – unsustainable agriculture, overfishing, unchecked urban expansion, and consumer-driven demand for wildlife products – requires systemic change in how societies produce, consume, and value nature.

Natural, mass, and human-driven extinction compared 🔗

To put everything in perspective, here’s how the three types of extinction differ:

Natural (background) extinction is slow, steady, and part of the normal evolutionary cycle. Species go extinct over millions of years, and new species evolve to take their place. The rate is roughly one extinction per million species per year.

Mass extinction is catastrophic but rare – it has happened only five times in the last 500 million years. Triggered by natural disasters like asteroid strikes or massive volcanic eruptions, these events wiped out 70-96% of species but were followed by eventual recovery over millions of years.

Anthropogenic extinction is rapid, ongoing, and caused by human activities. Species are disappearing at rates tens to hundreds of times higher than the average over the past 10 million years. Unlike previous mass extinctions, this one is being driven by a single species and is, in theory, entirely preventable.

The critical difference with anthropogenic extinction is that we have the knowledge and tools to stop it. Past mass extinctions were beyond any creature’s control. The current crisis is within ours.

What do you think? If human-driven extinction is the only mass extinction event that could potentially be prevented, what responsibility do individuals, governments, and corporations each bear in reversing the trend? And how might our relationship with nature need to change for future generations to inherit a biodiverse planet?

References

1. https://www.ipbes.net/news/Media-Release-Global-Assessment
2. https://eowilsonfoundation.org/what-is-the-half-earth-project/the-extinction-crisis/
3. https://www.science.org/doi/10.1126/sciadv.1400253
4. https://unfoundation.org/blog/post/key-findings-to-know-from-the-ipbes-report-on-biodiversity/
5. https://www.nhm.ac.uk/discover/what-is-mass-extinction-and-are-we-facing-a-sixth-one.html
6. https://iucn.org/resources/conservation-tool/iucn-red-list-threatened-species