Species extinction occurs when the last individual of a species dies, ending its evolutionary lineage permanently. Current extinction rates are estimated at 100 to 1,000 times the natural background rate — a pace not seen since the asteroid impact that wiped out the dinosaurs 66 million years ago. The IUCN Red List 2025 classifies 47,957 species as threatened with extinction out of 164,912 assessed, while the Living Planet Index documents a 73 per cent average decline in vertebrate populations since 1970. Habitat destruction is the primary driver, followed by overexploitation, climate change, invasive species, pollution, and disease — but conservation action has proven that extinctions can be prevented when resources and commitment align.
What is species extinction?
Extinction takes several forms. Biological extinction — the complete and irreversible loss of a species — occurs when the last individual dies. Functional extinction happens when so few individuals remain that reproduction becomes impossible or the species can no longer fulfil its ecological role. The northern white rhino, with only five individuals in captivity and none capable of natural breeding, is functionally extinct. Local extinction (extirpation) means a species disappears from a specific area while surviving elsewhere — as happened with the red kite in England before its successful reintroduction.
The IUCN formally declares a species extinct only after exhaustive surveys over a 50-year period fail to locate any individuals. This conservative approach means confirmed extinction figures almost certainly undercount the true number of species lost, particularly among invertebrates and fungi in tropical regions.
The background extinction rate — the natural pace at which species disappear through evolution and environmental change — is approximately 0.1 to 1 species per million species per year, based on the fossil record. A mass extinction event occurs when more than 75 per cent of species are lost within a geologically brief period. Earth has experienced five such events in 4.5 billion years.
What were the five mass extinctions?
| Event | When | Species lost | Primary cause | Recovery |
|---|---|---|---|---|
| Ordovician–Silurian | ~445 Mya | ~85% | Glaciation, ocean anoxia | 5–10 million years |
| Late Devonian | ~375 Mya | ~75% | Climate change, ocean dead zones | 7–10 million years |
| Permian–Triassic ("The Great Dying") | ~252 Mya | ~96% | Siberian volcanism, ocean acidification | 8–10 million years |
| Triassic–Jurassic | ~201 Mya | ~76% | Volcanism, climate warming | 4–5 million years |
| Cretaceous–Paleogene | ~66 Mya | ~75% | Chicxulub asteroid impact | 10+ million years |
Each mass extinction reshaped life on Earth. The Permian–Triassic event — "The Great Dying" — eliminated 96 per cent of marine species and 70 per cent of terrestrial vertebrate families, making it the most catastrophic event in our planet's history. The Cretaceous–Paleogene event, triggered by a 10-kilometre asteroid, ended the reign of non-avian dinosaurs and opened the way for mammalian diversification. In every case, recovery took millions of years.
Are we in a sixth mass extinction?
The scientific evidence is compelling. A landmark 2015 study by Ceballos and colleagues found that current extinction rates are approximately 100 times the background rate — a conservative estimate. The IPBES Global Assessment (2019), the most comprehensive biodiversity evaluation ever conducted, concluded that around one million species are threatened with extinction, many within decades.
The Living Planet Report 2024 documented a 73 per cent average decline in monitored vertebrate populations since 1970, based on tracking 35,428 populations across 5,871 species. Freshwater ecosystems have been hardest hit (83 per cent decline), with Latin America experiencing a staggering 94 per cent loss. These population collapses precede formal extinction and signal how many species are approaching the point of no return.
The IUCN Red List 2025 assessed 164,912 species and classified 29.1 per cent as threatened. Amphibians are the most imperilled vertebrate group (41 per cent threatened), followed by plants (41 per cent), mammals (25 per cent), reptiles (21 per cent), and birds (14 per cent).
Important nuances exist. Assessment efforts are heavily biased toward vertebrates and well-studied regions — tropical invertebrates, which comprise the vast majority of species diversity, remain vastly under-assessed. "Dark extinction" — the loss of species never described by science — means the true toll is likely five to ten times higher than documented figures suggest. Against this, approximately 20 species are rediscovered annually, offering both hope and a reminder of how incomplete our knowledge remains.
What causes species to go extinct?
Six interconnected drivers are responsible for the current extinction crisis. Critically, these threats rarely act alone — they interact synergistically, creating feedback loops that push species past recovery thresholds.
Habitat destruction and fragmentation is the dominant driver, implicated in roughly 50 per cent of threatened species declines. Around 40 per cent of terrestrial habitats have been converted to agriculture, urban development, or resource extraction. Tropical rainforests — home to over 80 per cent of terrestrial species — are shrinking by approximately 10 million hectares per year. Fragmented habitats isolate populations, preventing gene flow and reducing viable population sizes.
Overexploitation through hunting, fishing, and wildlife trade drives extinction of large-bodied and slow-reproducing species. The passenger pigeon, once numbering three to five billion individuals, was hunted to extinction by 1914. Today, pangolins are the world's most trafficked mammals, with over one million traded annually — all eight species are now threatened.
Invasive species contribute to 15 to 20 per cent of extinction cases globally, particularly on islands. Brown tree snakes introduced to Guam eliminated nine of 13 native forest bird species. In the UK, the grey squirrel has driven the red squirrel to endangered status through competition and disease transmission.
Climate change is projected to become the dominant driver by 2050. Species are attempting to track suitable conditions — terrestrial species are shifting poleward at 17 km per decade — but fragmented habitats and barriers prevent many from keeping pace. The Bramble Cay melomys became the first mammal officially attributed to climate change-driven sea-level rise in 2016.
Pollution causes sublethal effects — reduced reproduction, immune suppression — that often precede extinction. Neonicotinoid pesticides are driving pollinator decline, microplastics have been detected in 346 species, and nitrogen deposition degrades freshwater habitats across the UK and Europe.
Disease is an increasingly important factor. Chytrid fungus (Batrachochytrium dendrobatidis) has driven more than 500 frog species toward extinction and is responsible for approximately 7 per cent of amphibian extinctions since 1500. White-nose syndrome has caused bat population declines exceeding 90 per cent in affected North American hibernacula.
Which species have recently gone extinct?
At least 1,199 species have been documented as extinct since 1500, with the rate accelerating sharply since 1900. The 21st century has already recorded over 300 documented extinctions.
- Bramble Cay melomys (2016) — first mammal officially attributed to climate change; endemic to a tiny island in Torres Strait, Australia
- Spix's macaw (~2000 in the wild) — extinct in the wild; fewer than 400 survive in captivity with reintroduction efforts underway
- Christmas Island pipistrelle (2009) — last recorded individual detected in 2009; declared extinct by Australian authorities
- Golden toad (~2004) — Panamanian endemic driven to extinction by chytrid fungus
Some species teeter on the very edge. The vaquita porpoise, with approximately 10 individuals remaining, faces near-certain extinction from illegal gillnet fishing. The northern white rhino is functionally extinct, with five individuals in captivity and no prospect of natural breeding. The spoon-billed sandpiper survives with an estimated 100 to 500 individuals in Asian wetlands.
Occasionally, species thought lost reappear. The Wollemi pine, a "living fossil" presumed extinct for 150 million years, was rediscovered in Australian rainforest in 1994. The ghost orchid was found in an English woodland in 2024 after a 15-year absence. These "Lazarus species" offer hope but also underscore how much we still don't know about the natural world.
How does extinction affect the UK?
Britain has a long history of species loss. Wolves, lynx, and brown bears were all driven to extinction through hunting and persecution by the 18th century. The bittern disappeared as a breeding bird by 1868. More recently, the State of Nature 2023 report found that 16 per cent of UK species assessed are at risk of extinction — up from 13 per cent in 2016 — with farmland birds declining by 57 per cent and insects by 59 per cent since 1994.
Section 41 of the NERC Act 2006 identifies 943 priority species in England requiring conservation attention. The drivers of decline are familiar: agricultural intensification, habitat fragmentation, pollution, invasive species, and climate change.
But the UK also demonstrates that extinction can be reversed at the local level. Red kites now number approximately 1,800 breeding pairs following reintroduction from 1990. Beavers have been restored as a legally protected native species. The large blue butterfly, extinct in Britain in 1979, now thrives at 11 sites with populations exceeding 10,000. These successes prove that sustained conservation investment works.
Can we bring extinct species back?
De-extinction — using genetic technology to resurrect lost species — has captured public imagination. Colossal Biosciences is working to create a woolly mammoth–elephant hybrid using CRISPR gene editing, while the University of Melbourne's Extinct Diseases Group is attempting to reconstruct the thylacine (Tasmanian tiger) genome for insertion into marsupial surrogates.
The limitations are substantial. Ancient DNA is degraded and fragmentary. Gene sequences alone cannot specify behaviour, immunity, or ecosystem integration. Suitable surrogate species may not exist. And de-extincted animals would inhabit modern ecosystems vastly different from those in which they evolved.
The economics are telling: de-extinction projects cost £10 to £100 million per species with speculative success rates, while habitat protection for living species costs £100,000 to £1 million with proven 80 per cent effectiveness. Preventing extinction is orders of magnitude more cost-effective than attempting to reverse it — which is why the conservation community overwhelmingly prioritises protecting species we still have over resurrecting those we have lost.
Frequently asked questions
How fast are species going extinct today?
Current extinction rates are estimated at 100 to 1,000 times the natural background rate of 0.1 to 1 species per million species per year. A 2015 study by Ceballos and colleagues in Science Advances calculated a conservative estimate of 100 times the background rate. The IPBES Global Assessment (2019) concluded that approximately one million species are threatened with extinction, many within decades. At least 1,199 species have been documented as extinct since 1500, with the rate accelerating significantly since 1900.
What is the main cause of species extinction?
Habitat destruction and fragmentation is the single largest driver of modern species extinction, implicated in roughly 50 per cent of threatened species declines according to the IPBES Global Assessment. Approximately 40 per cent of terrestrial habitats have been converted to agriculture, urban development, or resource extraction. Other major drivers — overexploitation, climate change, invasive species, pollution, and disease — often interact synergistically, compounding the threat.
How many mass extinctions have there been?
Earth has experienced five mass extinctions over 4.5 billion years: the Ordovician–Silurian (~445 million years ago, ~85% of species lost), Late Devonian (~375 Mya, ~75%), Permian–Triassic (~252 Mya, ~96% — the worst), Triassic–Jurassic (~201 Mya, ~76%), and Cretaceous–Paleogene (~66 Mya, ~75%). Many scientists argue we are now in a sixth mass extinction driven by human activity, with current extinction rates 100 to 1,000 times the background rate.
What was the worst mass extinction?
The Permian–Triassic extinction approximately 252 million years ago — known as "The Great Dying" — was the most devastating, eliminating roughly 96 per cent of marine species and 70 per cent of terrestrial vertebrate families. It was triggered by massive volcanic eruptions in Siberia that released enormous quantities of CO₂, hydrogen sulphide, and methane, causing ocean acidification and anoxia. Recovery took 8 to 10 million years.
Can extinct species be brought back to life?
De-extinction research using CRISPR gene editing is underway for species like the woolly mammoth and thylacine, but remains experimental with no viable specimens produced as of 2026. Technical challenges include degraded ancient DNA, inability to replicate behaviour and immunity from genetics alone, and lack of suitable surrogate species. Critically, de-extinction costs £10–100 million per species with uncertain success, while habitat protection for living species costs £100,000–1 million with proven effectiveness. The scientific consensus is that preventing extinction is far more effective than reversing it.
Which animal groups are most at risk of extinction?
According to the IUCN Red List 2025, amphibians are the most threatened vertebrate group with 41 per cent of assessed species at risk, followed by mammals (25 per cent), reptiles (21 per cent), fish (16 per cent), and birds (14 per cent). Among plants, 41 per cent are threatened. Freshwater species are particularly vulnerable, with the Living Planet Index showing an 83 per cent population decline in freshwater ecosystems since 1970 — the steepest of any habitat type.
Extinction is not inevitable
The evidence for a sixth mass extinction is sobering — but the critical difference from the previous five is that this one is caused by human activity, and therefore within human power to stop. Every mass extinction in Earth's history was triggered by forces beyond any species' control: asteroid impacts, volcanic catastrophe, runaway climate change. Today's extinction crisis is driven by choices about land use, consumption, pollution, and carbon emissions — choices that can be changed.
The success of species recovery programmes worldwide demonstrates that extinction is not a one-way process when intervention comes in time. The challenge is scaling these successes — through habitat protection, policy reform, reduced consumption, and sustained investment in conservation — before we lose species that no amount of de-extinction technology will ever truly replace.
