Species extinction rates
We Are Not in a Mass Extinction. We Are in the Prelude.
The fossil record has witnessed five mass extinctions, and the scientists who study them most closely are the ones most disturbed by what they see happening right now.
The Idea
When palaeontologists talk about mass extinctions, they mean events that wiped out more than 75% of Earth's species — the end-Cretaceous asteroid, the Permian die-off so catastrophic it's called 'the Great Dying'. By that benchmark, what we're living through looks modest. A few hundred documented species lost in the last century. Surely that's not in the same conversation? The trap is timescale. In the fossil record, those ancient catastrophes look instantaneous — a sharp boundary in the rock. But they unfolded over thousands to tens of thousands of years. We are roughly a century into an acceleration, which means we are watching the opening movement of something that will only be legible in the geological record long after we're gone. The baseline extinction rate — the background hum of species loss that characterises stable geological periods — is roughly one to five species per year across all life on Earth. Current estimates, published in journals like Science and PNAS, put the actual rate somewhere between 100 and 1,000 times that. The IUCN Red List logs around 900 confirmed extinctions since 1500, but this almost certainly understates reality: most species go extinct before they are formally described. We are cataloguing a library while it burns. The deeper strangeness is that we are not just losing species — we are losing populations within species, which hollows out ecological function long before a creature technically disappears.
In the World
In 2017, biologists Gerardo Ceballos, Paul Ehrlich, and Rodolfo Dirzo published a paper in PNAS that introduced a term designed to stop people hiding behind the species-count debate: 'biological annihilation'. Their argument was that focusing on species extinction missed the real story. They looked at 27,600 terrestrial vertebrate species and found that nearly a third had declining populations. They then examined 177 mammal species in granular detail and discovered that all of them had lost at least 30% of their geographic range since 1900. Many had lost over 80%. Their case study for a species the world assumed was fine: the lion. Lions are not on the brink of extinction by most formal measures. But in the 1990s, lion populations collapsed by around 43% in just two decades. Today, they are absent from over 90% of their historical range. The species persists — the ecological reality of the lion in the world has been devastated. This distinction matters because a species reduced to a remnant population has already lost most of what it contributed: its seed dispersal, its predation pressure, its role in nutrient cycling. Biological annihilation describes a world that still technically contains lions and elephants and sharks, but functions as if it doesn't — a planet running on ecological fumes while the headline species count flatters us into complacency.
Why It Matters
The honest reason this is hard to sit with is that extinction is irreversible in a way that almost nothing else in environmental science is. Carbon can, in principle, be pulled from the atmosphere. Rivers can be cleaned. Forests can regrow. A species, once gone, takes evolution millions of years to approximate again — and the web of relationships it anchored cannot be reconstructed on any human timescale. Knowing this sharpens a particular kind of attention. It makes the presence of other living things feel less like backdrop and more like company — company that is quietly, steadily becoming rarer. It also reframes what 'nature' means: the ecosystems most of us have access to are already impoverished versions of what existed two or three centuries ago. We calibrate our sense of normal to a world already in loss. That recalibration — called 'shifting baseline syndrome' by the marine biologist Daniel Pauly — might be one of the most important concepts in conservation. Recognising it doesn't necessarily lead to despair. It can lead to genuine curiosity about what was, and what still could be.
A Question to Ponder
If most extinctions happen before a species is even named, what does it mean to try to protect something you don't yet know exists?
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