Extinction happens when the last member of a species dies. A species may be functionally extinct before the last member dies if it can no longer reproduce or recover. Determining when a species becomes extinct is difficult because its potential range may be very large. This is usually decided later, after the fact. This difficulty can lead to Lazarus taxa, where a species thought to be extinct is found again (often in fossils) after a long time of not being seen.
It is estimated that over five billion species have gone extinct. Scientists think there are about 8.7 million eukaryotic species today, and the number may be much higher when prokaryotes are included. Some well-known extinct animals include non-avian dinosaurs, saber-toothed cats, and mammoths. Species form through evolution, a process called speciation. Species become extinct when they can no longer survive due to changes in their environment or competition. The connection between animals and their roles in ecosystems is well understood. Most species disappear within 10 million years after they first appear, but some, called living fossils, remain almost unchanged for hundreds of millions of years, though this idea has been debated.
Mass extinctions are rare, but the loss of individual species or groups is common and part of natural evolution. Extinctions have only recently been recorded in detail, and a current mass extinction is happening because of human activities. Most extinct species are not officially documented. Some scientists predict that up to half of all plant and animal species may go extinct by 2100. A 2018 report said that the loss of 300 mammal species since the Late Pleistocene would take 5 to 7 million years to recover.
According to the 2019 Global Assessment Report by IPBES, wild mammal populations have dropped by 82%, natural ecosystems have lost about half their area, and one million species are at risk of extinction—mostly because of human actions. Twenty-five percent of plant and animal species are in danger of extinction. A later IPBES report said unsustainable fishing, hunting, and logging are major causes of the extinction crisis. In June 2019, one million species were at risk of extinction. At least 571 plant species have been lost since 1750. The main reason for these extinctions is habitat destruction from human activities, such as cutting down forests and turning land into farmland.
A dagger symbol (†) next to a species or group name usually means it is extinct.
Definition
A species is extinct when the last member of that species dies. Extinction is certain when no members of the species remain who can reproduce and create new offspring. A species may be functionally extinct if only a few individuals survive, but they are unable to reproduce due to poor health, old age, being spread out over a large area, not having enough individuals of both sexes (in species that reproduce sexually), or other reasons.
To determine if a species is extinct, scientists must have a clear definition of that species. For a species to be declared extinct, it must be clearly different from any ancestor or descendant species, as well as from closely related species. The extinction of a species or its replacement by a descendant species is an important idea in the punctuated equilibrium hypothesis, which is a theory about how species change over time.
In ecology, the term "extinction" is sometimes used to describe local extinction, where a species no longer lives in a specific area being studied, even though it still exists elsewhere. Local extinctions can sometimes be reversed by bringing individuals from other areas back to the original location. For example, wolves were reintroduced to certain regions after becoming locally extinct there. Species that are not globally extinct are called extant. Species that are extant but at risk of becoming extinct are called threatened or endangered species.
Today, an important focus is on efforts to protect species that are critically endangered. This is shown by the conservation status "extinct in the wild" (EW). Species listed as EW by the International Union for Conservation of Nature (IUCN) have no living members in the wild and are kept only in zoos or other artificial environments. Some of these species are functionally extinct because they no longer live in their natural habitat, and it is unlikely they will be returned to the wild. When possible, zoos and other institutions work to keep a healthy population of these species through planned breeding programs, which may help reintroduce them to the wild in the future.
The extinction of one species can lead to the extinction of other species, creating a "chain of extinction." This is especially common when a keystone species, which plays a critical role in its ecosystem, becomes extinct.
A 2018 study suggested that the sixth mass extinction, which began in the Late Pleistocene, could take up to 5 to 7 million years to restore mammal diversity to levels seen before the human era.
The extinction of a parent species, while its descendant species or subspecies still exist, is called pseudoextinction or phyletic extinction. In this case, the older species disappears and is either transformed into a new species (anagenesis) or split into multiple new species (cladogenesis).
Pseudoextinction is hard to prove unless there is strong evidence linking a living species to a previous one. For example, some scientists argue that Hyracotherium, an early horse, may be pseudoextinct instead of extinct because modern horses (like zebras and donkeys) still exist. However, since fossil species usually do not leave genetic material behind, it is unclear whether Hyracotherium evolved into modern horses or simply shared a common ancestor with them. Pseudoextinction is easier to confirm for larger groups of species, such as families or orders.
A Lazarus taxon or Lazarus species is a term used when a species or group of species thought to be extinct is later found to still exist. It can also describe cases where a species appears in the fossil record again after a long gap, even if it eventually becomes extinct.
The coelacanth, a fish related to lungfish and tetrapods, is an example of a Lazarus species. It was only known from fossils and thought to be extinct since the end of the Cretaceous Period. However, a living coelacanth was discovered in 1938 off the coast of South Africa. Another example is Calliostoma bullatum, a deepwater sea snail. It was originally described from fossils in 1844 but was rediscovered in 2019.
Attenborough's long-beaked echidna (Zaglossus attenboroughi), a mammal from Papua New Guinea, was last seen in 1962 and thought to be extinct. It was rediscovered in 2023.
Some species once thought to be extinct are still the subject of speculation about their possible existence. If they are found again, they would be considered Lazarus species. Examples include the thylacine (or Tasmanian tiger), which was last seen in 1936; the Japanese wolf, last sighted over 100 years ago; the American ivory-billed woodpecker, last confirmed in 1944; and the slender-billed curlew, not seen since 2007.
Causes
Species have been disappearing throughout their history as they evolved. Scientists believe that more than 99.9% of all species that ever existed are no longer alive. On average, a species lives for 1 to 10 million years, though this time varies depending on the type of organism. Many factors can cause a species to go extinct, either directly or indirectly. Beverly and Stephen C. Stearns wrote, "Each extinction has unique causes—some are complex, others are simple." A species becomes extinct when it cannot survive or reproduce in its environment and cannot move to a new environment where it can. Extinction can happen suddenly, such as when pollution makes an entire habitat uninhabitable, or it can occur slowly over thousands or millions of years, such as when a species loses competition for food to better-adapted species. Sometimes, extinction happens long after the event that started it, a process called extinction debt.
Scientists debate whether genetic factors or environmental factors are more important in causing extinction, similar to the discussion about whether nature or nurture influences human traits. Some argue that extinctions in the fossil record were caused by evolution, competition, predation, disease, or disasters, but no single explanation fits all cases. Conservation biology uses a model called the extinction vortex to classify causes of extinction. Concerns about human extinction, as discussed in books like Our Final Hour, focus on climate change or technological disasters.
Human-driven extinction began when humans migrated out of Africa more than 60,000 years ago. Today, environmental groups and governments work to prevent species loss through conservation programs. Humans cause extinction by overharvesting, pollution, habitat destruction, introducing invasive species, and overhunting. Rapid human population growth and high consumption rates are major causes of the current extinction crisis. According to the International Union for Conservation of Nature (IUCN), 784 species have gone extinct since 1500, though many more may have been missed. Some species have been listed as extinct since 2004.
If a population cannot adapt quickly enough to environmental changes or the buildup of harmful genetic changes, it may go extinct. Smaller populations have fewer beneficial genetic changes and are more likely to accumulate harmful mutations, which can lead to a cycle of reduced fitness and extinction. Limited geographic range is a key factor in extinction during normal times but becomes less important during mass extinctions.
Extinction rates depend not only on population size but also on factors that affect a species’ ability to adapt, such as genetic diversity, competition, and environmental changes. A population with a wide variety of genes has a better chance of surviving sudden changes. Loss of genetic diversity, such as through population bottlenecks, increases the risk of extinction.
Extinction can occur when species adapted to specific environments face genetic pollution, such as uncontrolled mixing with other species. This can happen when humans introduce new species or alter habitats, bringing previously isolated species together. Rare species are especially vulnerable to being outcompeted or hybridized by more common species. These extinctions may not always be obvious from physical traits alone.
The gene pool of a species includes all the genetic information in its members. A large gene pool helps populations survive intense selection pressures, while low genetic diversity weakens a species’ ability to adapt. Replacing native genes with foreign ones reduces genetic diversity, increasing the risk of extinction.
Habitat degradation is the leading human-caused reason for species extinction. Agriculture is the main cause of habitat degradation worldwide, followed by urban development, logging, mining, and certain fishing practices. Degraded habitats can make survival impossible for species by making environments toxic or reducing their ability to compete for resources.
Habitat destruction, such as removing plants that hold soil together, increases erosion and reduces nutrients in ecosystems. This can lower agricultural productivity and harm water quality by increasing sediment and pollution in rivers. Toxic habitats can kill species quickly or over time by affecting their lifespan, reproduction, or ability to compete.
Habitat degradation can also destroy specific environments, such as tropical rainforests replaced by open land. Species that depend on dense forests, like shade-loving plants, may not survive without shelter. Similarly, ocean floor destruction from fishing practices can eliminate habitats for marine life.
Degraded habitats often lead to fewer resources or new competitors. Global warming has allowed some species to move into new areas, where they may outcompete or prey on local species. Vital resources like water may also become scarcer, further threatening survival.
Mass extinctions
There have been at least five mass extinctions in Earth's history, and four of these happened in the last 350 million years. During these events, many species disappeared quickly in geological terms. One possible cause of the Permian–Triassic extinction event, which occurred about 250 million years ago, was a large volcanic eruption that sent a lot of volcanic ash into the atmosphere. This event is believed to have caused the extinction of about 90% of species at that time. Evidence also suggests that this event followed another mass extinction called Olson's Extinction. The Cretaceous–Paleogene extinction event, which happened 66 million years ago, is best known for ending the age of non-avian dinosaurs, along with many other species.
A 1998 survey of 400 biologists by the American Museum of Natural History in New York found that nearly 70% believed Earth is now in the early stages of a mass extinction caused by humans, called the Holocene extinction. The same number of scientists thought that up to 20% of all living species might go extinct by 2028. A 2014 issue of the journal Science noted that many scientists agree humans are causing large-scale species loss. A 2020 study in PNAS said the current extinction crisis could be the most serious environmental threat to human civilization because it cannot be reversed. A 2025 study found that human activities are responsible for the loss of biodiversity across all species and ecosystems.
In 2002, biologist E. O. Wilson estimated that if humans continue destroying the environment at the current rate, half of all plant and animal species could be extinct in 100 years. Scientists also say the current rate of species extinction is 100 to 1,000 times faster than the average rate in Earth's history, and future rates could be 10,000 times higher. Some species are disappearing even faster. Scientists like Paul R. Ehrlich and Stuart Pimm say human population growth and overuse of resources are the main causes of the modern extinction crisis.
In January 2020, the UN's Convention on Biological Diversity created a plan to reduce the extinction crisis. The plan aims to protect 30% of Earth's land and oceans by 2030, cut pollution by 50%, and restore ecosystems by 2050. A 2020 report by the United Nations said only six of 20 biodiversity goals set in 2010 were "partially achieved" by 2020. The report warned that biodiversity loss will continue unless current habits change, especially overuse of resources, population growth, and technology. A 2021 study in Frontiers in Conservation Science said even meeting the 2010 goals would not have stopped biodiversity loss. The report also said countries have not prioritized biodiversity protection, focusing more on jobs, health, and economic growth instead.
History of scientific understanding
For much of history, the idea that extinction means the end of a species was not widely accepted. Before the 19th century, many people in Western societies believed the world was created by God and was complete and perfect. This belief was especially strong in the 1700s, when a religious idea called the "great chain of being" was popular. This idea suggested all living things, from tiny microbes to God, were connected in a single, unbroken chain. Under this model, extinction was impossible because it would create gaps in the chain and break the natural order. Thomas Jefferson supported this idea and denied the extinction of the woolly mammoth, believing nature would never allow an animal species to disappear.
In the late 17th century, scientists discovered fossils that looked unlike any living species. To explain these findings, scientists tried to fit them into existing ideas that did not allow for total extinction. In 1686, Robert Hooke showed the Royal Society a fossil of a nautilus that was over two feet in size and looked different from any known living species. He thought the species might still exist in the deep ocean. Similarly, in 1695, Sir Thomas Molyneux described large antlers found in Ireland that did not match any living species. He believed the antlers came from a North American moose that once lived in the British Isles. Molyneux argued that while species could disappear from certain areas, they could never be completely lost and would exist elsewhere. These ideas were hard to prove wrong because many parts of the world were not yet fully explored.
In 1796, Georges Cuvier introduced the modern idea of catastrophic extinction in a lecture to the French Institute. He spent much of his career trying to convince scientists of his theory. Cuvier was a respected paleontologist who could reconstruct the anatomy of unknown species from bone fragments. His main evidence for extinction came from mammoth skulls found near Paris. He noticed these skulls were different from living elephants and argued it was unlikely such a large animal would be unknown. In 1798, he studied a fossil from the Paris Basin, originally found by Robert de Lamanon in 1782. At first, he thought it belonged to a dog, but later decided it was from an unknown animal. This led to the naming of the extinct mammal genus Palaeotherium in 1804. Cuvier also identified another extinct genus, Anoplotherium, which shared some traits with living animals like ruminants and rhinoceroses but had unique features. In 1812, Cuvier and other scientists mapped the layers of rock in the Paris Basin. They found alternating saltwater and freshwater deposits and patterns of fossils appearing and disappearing. From this, Cuvier concluded that the Earth had experienced cycles of catastrophic flooding, extinction, and the return of new species.
Cuvier’s fossil evidence showed that life on Earth had changed over time, a fact most scientists accepted. However, they debated whether these changes happened gradually or suddenly. Cuvier believed extinction was caused by large, sudden events that wiped out many species at once. In his 1813 book Essay on the Theory of the Earth, he argued that extinct species were destroyed by repeated catastrophic floods. His ideas faced opposition from scientists who supported the theory of uniformitarianism, which suggested that past events followed the same slow processes seen today.
Jean-Baptiste Lamarck, a scientist who worked with Cuvier, believed species could change over time. While he did not deny extinction, he thought it was rare and that most changes in species happened gradually. Unlike Cuvier, Lamarck doubted that large-scale disasters could cause total extinction. In his work Hydrogeologie, he argued that Earth’s surface was shaped by slow water erosion and that species adapted to changing environments over time.
Charles Lyell, a geologist and founder of uniformitarianism, believed past events should be explained using present-day processes. He acknowledged extinction, citing examples like the dodo and the loss of horses in the British Isles. However, he rejected the idea of mass extinctions, believing all changes happened slowly. Lyell also showed that Cuvier’s interpretation of the Paris Basin’s layers was incorrect. Instead of catastrophic floods, Lyell explained the saltwater and freshwater deposits as the result of slow changes in sea levels.
The idea of extinction was central to Charles Darwin’s On the Origin of Species, where he described how less fit species disappeared due to competition. Darwin believed extinction was a natural result of species competing for resources. His work led to the widespread acceptance of gradual extinction, now called "background extinction." It was not until 1982, when David Raup and Jack Sepkoski published their research on mass extinctions, that Cuvier’s theory of catastrophic extinction was supported again. Today, scientists understand extinction as a combination of both sudden, large-scale events and slower, ongoing changes.
Human attitudes and interests
Extinction is a key topic studied in zoology and biology. It has also become a concern for people outside the scientific community. Organizations like the Worldwide Fund for Nature work to protect species from disappearing. Governments have passed laws to stop habitat destruction, overuse of land for farming, and pollution. Many extinctions caused by humans have been accidental, but some species have been deliberately destroyed, such as dangerous viruses. Other species have been driven to extinction due to poaching or because they were considered "undesirable" for human goals. For example, the American bison was nearly wiped out by government-sanctioned hunts to force Native Americans to leave their lands, as many relied on bison for food.
Biologist Bruce Walsh explains that scientists care about preserving species for three reasons: genetic resources, ecosystem stability, and ethics. Today, scientists emphasize the importance of keeping biodiversity alive.
In modern times, businesses must deal with how their activities affect plants and animals. Some technologies, like DDT, have little harm to humans but can be harmful to wildlife. Biogeographer Jared Diamond notes that while companies may dismiss environmental concerns as exaggerated, some choose to protect nature by supporting conservation efforts.
Governments sometimes view the loss of native species as a loss to ecotourism and create strict laws to stop the trade of native species. Nature preserves are established to provide habitats for species pushed out by human growth. The 1992 Convention on Biological Diversity led to international plans to guide governments in protecting biodiversity. Groups like The Wildlands Project and the Alliance for Zero Extinctions educate the public and push governments to act.
People living close to nature depend on all species for survival, making them vulnerable to extinction risks. However, people often prioritize daily needs over conservation. In tropical developing countries, human overpopulation has led to deforestation through farming methods like slash-and-burn, which harms endangered species’ habitats.
Antinatalist philosopher David Benatar says concerns about species extinction usually come from worries about how losing species might affect humans. He argues that people rarely consider the loss of non-human species in the same way as human losses. Anthropologist Jason Hickel suggests humans are indifferent to large-scale species extinction because we see ourselves as separate from nature, influenced by capitalism’s view of nature as resources to exploit.
The smallpox virus is extinct in the wild, though samples remain in labs. The rinderpest virus, which infected cattle, is also extinct in the wild. Poliovirus is now limited to small areas due to eradication efforts. The Guinea worm, which causes a disease, is nearly eradicated thanks to work by the Carter Center. A bacterium that causes yaws is being eradicated.
Biologist Olivia Judson has proposed deliberately eliminating certain disease-carrying mosquitoes. She suggests using genetic changes to reduce their populations, arguing that removing 30 mosquito species could save millions of lives while only slightly reducing genetic diversity. She claims ecosystems can adapt to species loss without major harm. Anti-malarial programs have limited success in helping people in developing nations. If these efforts fail, she suggests considering extreme measures.
Biologist E. O. Wilson supports eradicating mosquitoes that spread diseases like malaria. He argues it is reasonable to remove species that harm humans.
Efforts have successfully reduced tsetse flies and their parasites in parts of Africa, including the island of Príncipe. Current efforts aim to eliminate them across Africa, seen as beneficial and morally necessary.
Some scientists, like Harvard’s George M. Church, believe technology may allow extinct species to be brought back through cloning using DNA from remains. Proposed candidates include the mammoth, thylacine, dodo, and Pyrenean ibex. For cloning to work, enough individuals would need to be created from DNA of different animals to form a sustainable population. Though some question the ethics, cloning extinct species is theoretically possible.
In 2003, scientists tried to clone the Pyrenean ibex. Of 285 cloned embryos, only two survived for two months before dying. A second attempt produced one live clone, which died seven minutes later due to lung defects.