Wikipedia Deep Dive

Holocene extinction

13 min read

We are living through a mass extinction. Right now. As you read this sentence, species are vanishing from Earth at a rate not seen since an asteroid slammed into the Yucatán Peninsula sixty-six million years ago and ended the reign of the dinosaurs.

That's not hyperbole. That's the scientific consensus.

The Numbers Are Staggering

The normal rate at which species go extinct—what scientists call the "background extinction rate"—is a slow, steady trickle. Species evolve, flourish for a while, and eventually disappear, replaced by their descendants or competitors. This has been happening for billions of years. It's the natural heartbeat of evolution.

Today, that heartbeat has become a cardiac arrest. Current extinction rates are estimated at one hundred to one thousand times higher than normal. Some researchers put the figure even higher—up to ten thousand times the background rate. Even the most conservative estimates paint a picture of biological catastrophe.

A 2023 study published in the Proceedings of the National Academy of Sciences calculated that at least seventy-three genera of animals have vanished since 1500. A genus is the taxonomic category above species—think of it as an entire branch of the tree of life rather than a single twig. Without human interference, those same seventy-three genera would have taken eighteen thousand years to disappear naturally. The authors concluded that we are causing "the rapid mutilation of the tree of life."

What Makes This a Mass Extinction?

Mass extinctions aren't just periods of elevated species loss. They're defined by a specific, terrifying threshold: the disappearance of at least seventy-five percent of all species within a geologically brief period—less than two million years. Earth has experienced five of these apocalyptic events before.

The most famous is the Cretaceous-Paleogene extinction, the one that killed the non-avian dinosaurs. But there have been others. The Permian-Triassic extinction, sometimes called "the Great Dying," wiped out roughly ninety percent of all species on Earth. The oceans became so hostile to life that coral reefs disappeared entirely for millions of years.

The question scientists have debated isn't whether we're losing species at an alarming rate. We clearly are. The debate is whether we've crossed the threshold into a true mass extinction, or whether we're merely on the precipice.

In 2017, over fifteen thousand scientists from one hundred eighty-four countries signed a document called "World Scientists' Warning to Humanity: A Second Notice." Their conclusion was unambiguous: "We have unleashed a mass extinction event, the sixth in roughly 540 million years."

Some researchers prefer more cautious language. Stuart Pimm, a theoretical ecologist who has spent his career studying extinction rates, argues that the sixth mass extinction "is something that hasn't happened yet—we are on the edge of it." But even Pimm acknowledges that extinction rates for plants alone are one hundred times higher than normal.

Whether we've crossed the line or merely have one foot over it seems like a distinction without much practical difference.

The Guilty Party

There's no mystery about what's causing this extinction. We are.

The Holocene is the current geological epoch, which began roughly twelve thousand years ago at the end of the last ice age. Some scientists prefer the term "Anthropocene extinction" because it emphasizes the role of anthropos—the Greek word for human. The Anthropocene, a proposed new geological epoch, would mark the point at which human activity became the dominant force shaping Earth's geology and ecosystems. The term was coined in 2000, and while it hasn't been officially adopted—the International Commission on Stratigraphy rejected the proposal in 2024—the concept captures something real about our moment in history.

The mechanisms of destruction are familiar: habitat destruction, deforestation, overfishing, pollution, the introduction of invasive species, the spread of diseases through livestock and crops, and increasingly, climate change. What's less familiar is the sheer scale.

A 2018 study found that since the dawn of human civilization, the total mass of wild mammals on Earth has decreased by eighty-three percent. Let that sink in. More than four-fifths of wild mammal biomass has vanished since we started building cities and planting crops.

The breakdown is even more striking. Today, livestock make up sixty percent of all mammalian biomass on Earth. Humans account for thirty-six percent. Wild mammals? Just four percent.

Birds tell a similar story. Seventy percent of all birds on Earth are now domesticated poultry—chickens, mostly. Only thirty percent are wild.

We haven't just become the dominant species on the planet. We've reshaped the entire animal kingdom in our image.

A History of Destruction

Human-caused extinction isn't a modern phenomenon. It's been happening since the Late Pleistocene, more than twelve thousand years ago, when our ancestors first spread across the globe.

Everywhere humans went, megafauna—large animals—disappeared. The correlation is too consistent to be coincidental. When humans arrived in Australia roughly fifty thousand years ago, giant wombats the size of cars and marsupial lions went extinct. When humans crossed into the Americas perhaps fifteen thousand years ago, mammoths, mastodons, giant ground sloths, and saber-toothed cats vanished. When Polynesians reached new islands across the Pacific, flightless birds and endemic species disappeared within centuries or even decades.

The pattern repeated on every continent except Africa, where megafauna had co-evolved with humans and learned to fear us. Even there, Africa's large animals are now in steep decline.

Over the past one hundred twenty-five thousand years, the average body size of wildlife has fallen by fourteen percent as prehistoric and modern humans eliminated large animals worldwide. Big animals make tempting targets—they provide more meat per hunt—and they tend to reproduce slowly, making their populations vulnerable to even modest hunting pressure.

The arrival of agriculture accelerated the destruction. Farming requires land, and the more land under cultivation, the more people a civilization can support. For ten thousand years, humans have been converting forests and wetlands—biodiversity hotspots teeming with countless species—into fields and pastures, which support far fewer wild creatures. This process has dramatically reduced Earth's capacity to sustain wild bird and mammal populations.

Only in more recent centuries have plants suffered extensive losses as well, as deforestation and land conversion have accelerated beyond anything our ancestors could have imagined.

The Global Superpredator

A 2015 study in the journal Science introduced a striking concept: humans are "global superpredators," unlike anything that has existed before.

Normal predators don't eliminate their prey entirely—doing so would be evolutionary suicide. Predator and prey populations tend to oscillate in a dynamic equilibrium. When prey becomes scarce, predators starve and their numbers decline, allowing prey populations to recover.

Humans broke this pattern. We hunt apex predators—the top predators in their ecosystems—at rates that no natural system can sustain. We kill adult animals in their prime, which is the opposite of how natural predation usually works. We don't stop hunting when prey becomes scarce; we just move on to something else, or we subsidize our hunting with agriculture.

We are predators with refrigerators, and that makes us uniquely dangerous.

What We're Losing

The 2019 Global Assessment Report on Biodiversity and Ecosystem Services, published by the United Nations, estimated that one million species are currently at risk of extinction within decades. A 2023 follow-up study doubled that estimate to two million species.

The World Wide Fund for Nature's 2020 Living Planet Report found that wildlife populations have declined by sixty-eight percent since 1970. Their 2022 update found the decline had reached almost seventy percent. That's not sixty-eight percent of species gone—it's sixty-eight percent of individual animals.

Imagine a forest with a thousand birds in 1970. Today, that same forest has roughly three hundred.

A 2023 study examining seventy thousand monitored species found that forty-eight percent are experiencing population declines due to human pressures. Only three percent have increasing populations.

Edward O. Wilson, the legendary biologist who died in 2021, predicted in his 2002 book "The Future of Life" that if current trends continue, half of Earth's higher lifeforms could be extinct by 2100. More recent studies support his grim forecast. A 2022 study projected that if global warming continues unchecked, between thirteen and twenty-seven percent of terrestrial vertebrate species could be driven to extinction by century's end.

But extinction is only part of the story. A 2021 study found that only around three percent of Earth's terrestrial surface remains "ecologically and faunally intact"—meaning areas that still have healthy populations of native species with minimal human footprint. Ninety-seven percent of the land has been significantly degraded.

The Heart of the Crisis

Some researchers argue that focusing on species extinction misses the more immediate catastrophe: population extinction.

Paul Ehrlich, the Stanford biologist famous for his controversial 1968 book "The Population Bomb," has spent recent decades studying what he calls "biological annihilation." His argument, developed with collaborators including Rodolfo Dirzo, is that the disappearance of local populations—even when the species itself survives somewhere—represents an "existential threat" that most people, including many scientists, don't fully grasp.

Think of it this way: if elephants go extinct in Kenya but survive in a zoo in San Diego, the species technically persists. But the ecological role that elephants played in Kenya—dispersing seeds, creating water holes, shaping vegetation patterns—is gone. The ecosystem that depended on those elephants is diminished.

Multiply this by thousands of species and millions of local populations, and you begin to see the scope of what we're losing: not just species, but the intricate web of relationships that makes ecosystems function.

Why This Matters

The UNDP's 2020 Human Development Report put it bluntly:

Numerous experts believe we are living through, or on the cusp of, a mass species extinction event, the sixth in the history of the planet and the first to be caused by a single organism—us.

The 2019 UN report on biodiversity was even more alarming, warning that "organized human existence" itself is "jeopardised by increasingly rapid destruction of the systems that support life on Earth."

This isn't tree-hugging sentimentality. Ecosystems provide services that human civilization depends on: pollination of crops, purification of water, regulation of climate, cycling of nutrients, control of pests and diseases. When ecosystems collapse, these services disappear, and no amount of technology has yet proven capable of replacing them at scale.

The 2021 Economics of Biodiversity review, commissioned by the UK government, concluded that "biodiversity is declining faster than at any time in human history" and warned of severe economic consequences.

The Drivers of Destruction

In 2022, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services—known by its acronym IPBES—listed the primary drivers of the extinction crisis: unsustainable fishing, hunting, and logging; habitat destruction; pollution; climate change; and invasive species.

Agriculture looms behind many of these factors. Farming is the single largest cause of habitat destruction. The demand for meat drives deforestation, as forests are cleared for cattle ranching or to grow feed crops for livestock. Fertilizer runoff from farms creates dead zones in coastal waters. Pesticides kill far more than their intended targets.

Climate change adds another layer of stress. As temperatures rise, species must migrate to survive, but habitat fragmentation often blocks their path. Coral reefs are bleaching as ocean temperatures climb. Ocean acidification—caused by the absorption of excess carbon dioxide—threatens shellfish and the entire marine food web.

Human population growth and increasing consumption, particularly among affluent societies, amplify all of these pressures. There are now eight billion humans on Earth, each demanding resources, space, and energy.

Can We Stop It?

The honest answer is: we don't know.

We know what's causing the crisis. We know many of the solutions: protecting and restoring habitats, reducing consumption, transitioning away from fossil fuels, reforming agriculture, controlling invasive species, ending overfishing. These aren't mysteries.

The challenge is implementation. Every solution requires changing how billions of people live, and how powerful economic interests operate. The forces driving extinction—economic growth, population growth, consumption—are the same forces that many societies equate with progress and prosperity.

The scientists who signed the 2017 "Warning to Humanity" laid out a stark choice: "Soon it will be too late to shift course away from our failing trajectory, and time is running out."

Five years later, in 2022, a follow-up study in Science Advances warned that current trends "could result in the loss of more than a tenth of plant and animal species by the end of the century." That's a best-case scenario that assumes we make significant changes.

The worst-case scenarios are much darker.

Living in the Sixth Extinction

What does it mean to live through a mass extinction?

For most people, most of the time, it means nothing perceptible. The species disappearing are mostly ones we've never heard of—invertebrates, amphibians, plants in tropical forests. Even the more charismatic losses often happen far away, to creatures most of us will never see in person.

This invisibility is part of the problem. A 1998 survey found that seventy percent of biologists acknowledged an ongoing anthropogenic extinction event, but the general public remains largely unaware. Ehrlich and Dirzo argue that even many scientists don't fully grasp the scale of the crisis because they focus on species extinction rather than the more immediate collapse of populations.

But the effects are there if you know where to look. The decline in insect populations—sometimes called the "insect apocalypse"—is visible to anyone old enough to remember car windshields covered in bug splatter on summer drives. The silence in forests that once rang with birdsong. The empty nets of fishermen who remember more abundant catches.

Perhaps most haunting is what we'll never know we lost. Every species that goes extinct takes with it evolutionary innovations honed over millions of years—chemical compounds that might have become medicines, ecological relationships we never studied, beauty we never witnessed.

The tree of life that took four billion years to grow is being pruned in decades, and we're holding the shears.

A Note on Terminology

You may encounter different names for this phenomenon. "Holocene extinction" emphasizes that it's happening during the current geological epoch. "Anthropocene extinction" emphasizes human causation. "Sixth extinction" places it in the context of Earth's five previous mass extinctions. Some use "sixth mass extinction" to emphasize the severity, while others argue we haven't quite reached mass extinction thresholds yet and prefer "biodiversity crisis" or "extinction event."

These distinctions matter to scientists, but they can obscure the underlying reality: we are causing the most rapid loss of species in sixty-six million years, and possibly ever, given that no previous mass extinction had a single biological cause with the capacity to understand what it was doing.

We are the asteroid. But unlike the asteroid, we have a choice.