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A sixth mass extinction?
since c. 1500 (debated)· Extinction or crisis· Animals
DebatedScientists disagree about when, how or why.
Many scientists argue human activity is driving a sixth mass extinction; others say losses so far fall short of that label.
See it on the Life map →What happened
Since 1500, about 900 species are documented as extinct, from the dodo to the passenger pigeon, and the true number is surely higher because most species have never been described. Current extinction rates are estimated at tens to hundreds of times the natural background rate. A 2019 UN-backed assessment (IPBES) estimated about one million species are threatened. The main causes are habitat loss, hunting and fishing, invasive species, pollution and climate change.
Why it matters
Losing species weakens the ecosystems that supply food, clean water, pollination and fisheries, and extinction, unlike most environmental damage, cannot be reversed.
Think of it like
Like rising vacancy across a portfolio: not yet a collapse, but if the trend holds long enough, it ends in one.
The evidence (fossils, genes, rocks)
The IUCN Red List tracks the status of more than 160,000 species; fossil records give background rates for comparison; field surveys show steep declines in many populations.
Still debated
Whether it counts as a 'mass' extinction: each of the Big Five removed roughly three-quarters of species, and documented losses so far are a small fraction of that.
Inside this (1)
Connections (6)
▸A sixth mass extinction? may have begun with Ice-age megafauna extinctionsDebated
The connection
Some scientists argue today's extinction crisis did not start in 1500 but with the ice-age megafauna losses, as modern humans spread across continents. On this view, one human-driven wave continued through island extinctions, such as Madagascar's giant lemurs and New Zealand's moa, to habitat loss and climate change today.
When and how
From about 50,000 years ago in Australia and about 13,000 in the Americas, to about 1,000–600 years ago on Madagascar and New Zealand.
How sure are we?
Extinction waves repeatedly follow human arrival on continents and islands; the pattern is clearest on islands, where timing is best known.
Debates and open questions
How much of the ice-age losses were human-caused, and whether lumping them with modern extinctions clarifies or blurs very different processes.
▸Human-caused climate change worsens A sixth mass extinction?Strong evidence
The connection
Climate change adds to habitat loss, hunting and invasive species. Warming pushes species toward the poles and uphill; those with nowhere to go, such as mountaintop and polar species, are squeezed. Reef corals bleach in marine heatwaves. The Bramble Cay melomys, a small Australian rodent, is considered the first mammal extinction caused mainly by climate change.
When and how
Worldwide; the Bramble Cay melomys, in Australia's Torres Strait, was confirmed extinct in 2016; global coral bleaching events struck in 1998, 2010, 2014–17 and 2023–25.
How sure are we?
Field studies document thousands of species shifting ranges; repeated reef bleaching tracks measured heatwaves; rising sea and storm surges wiped out the melomys's tiny island habitat.
Debates and open questions
How many species warming will eliminate; the IPCC puts about 3–14% of land species at very high risk at 1.5°C, rising steeply with further warming.
▸A sixth mass extinction? is often cited as a sign of The AnthropoceneDebated
The connection
Species are now vanishing far faster than the natural background rate, through habitat loss, hunting, invasive species and climate change. These losses, plus the global mixing of species, will leave a fossil record that future geologists could read as a boundary, much as past mass extinctions mark the boundaries between geological periods.
When and how
Worldwide, since about 1500; popularized by Richard Leakey and Roger Lewin's The Sixth Extinction (1995) and Elizabeth Kolbert's book of the same name (2014).
How sure are we?
The IUCN Red List documents roughly 900 extinctions since 1500, and a 2019 UN-backed assessment (IPBES) estimated about a million species are threatened.
Debates and open questions
Whether losses have reached mass-extinction scale, usually about 75% of species, or are only heading there; the proposed formal marker was plutonium fallout, not extinctions.
▸Dodo extinction became a symbol of A sixth mass extinction?Well established
The connection
The dodo's rapid disappearance after people reached Mauritius, through hunting, introduced animals and forest loss, captures the main drivers of modern extinctions in one story. Its fame, from Lewis Carroll's Alice in Wonderland (1865) to the phrase 'dead as a dodo', made it the symbol of human-caused extinction and the emblem of Mauritius.
When and how
Mauritius, Indian Ocean, from the Dutch arrival in 1598 to the last confirmed sighting in 1662; its symbolic role grew in the 1800s.
The evidence
Historical accounts and fossils document the extinction; its symbolic role shows in literature, Mauritius's coat of arms and conservation logos such as the Durrell trust's.
Debates and open questions
Whether hunting or introduced animals did more harm, and whether planned de-extinction efforts honor the symbol or distract from protecting living species.
▸A sixth mass extinction? would add a sixth to Extinction & mass extinctionsDebated
The connection
Each of the Big Five removed roughly three-quarters or more of species within a geologically short time. Some biologists argue that current loss rates, if continued, would reach that level within a few centuries. That would make the present the sixth mass extinction, and the first caused by a single species.
When and how
Term popularized by Richard Leakey and Roger Lewin's The Sixth Extinction (1995) and Elizabeth Kolbert's 2014 Pulitzer-winning book; quantified by Anthony Barnosky's team in Nature, 2011.
How sure are we?
Comparisons of modern extinction rates with fossil background rates; Barnosky's 2011 study estimated Big Five-level loss could come in about 240–540 years if threatened species are lost.
Debates and open questions
Comparing modern and fossil rates is tricky, since fossils miss many species and short time spans; some scientists argue the 'mass extinction' label is premature.
▸A sixth mass extinction? spurs attempts at De-extinction & the 2025 'dire wolf' claimWell established
The connection
Accelerating species losses motivate de-extinction groups, which pitch their tools as conservation aids too. Revive & Restore helped clone a black-footed ferret from cells frozen in 1988, adding genetic diversity to an endangered species. Colossal likewise says its methods can help threatened animals, not only lost ones.
When and how
Revive & Restore, founded 2012 by Stewart Brand and Ryan Phelan; Colossal, 2021; the cloned ferret Elizabeth Ann was born in Colorado in December 2020.
The evidence
The groups state this rationale openly, and the ferret clone and a cloned Przewalski's horse (2020) are real conservation results.
Debates and open questions
Critics warn it may divert funding from protecting habitat, or make extinction seem reversible and therefore less urgent.