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Extinction

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Conservation status
Bufo periglenes, the Golden Toad, was last recorded on May 15, 1989
Extinct
Threatened
Lower Risk

Other categories

Related topics

IUCN Red List category abbreviations (version 3.1, 2001)
Comparison of Red List classes above
and NatureServe status below
NatureServe category abbreviations
The thylacine (Thylacinus cynocephalus) is an example of an extinct species.
The thylacine (Thylacinus cynocephalus) is an example of an extinct species.

Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "reappears" (typically in the fossil record) after a period of apparent absence.

More than 99% of all species that ever lived on Earth, amounting to over five billion species,[1] are estimated to have died out.[2][3][4][5] It is estimated that there are currently around 8.7 million species of eukaryote globally,[6] and possibly many times more if microorganisms, like bacteria, are included.[7] Notable extinct animal species include non-avian dinosaurs, saber-toothed cats, dodos, mammoths, ground sloths, thylacines, trilobites, and golden toads.

Through evolution, species arise through the process of speciation—where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche—and species become extinct when they are no longer able to survive in changing conditions or against superior competition. The relationship between animals and their ecological niches has been firmly established.[8] A typical species becomes extinct within 10 million years of its first appearance,[5] although some species, called living fossils, survive with little to no morphological change for hundreds of millions of years.

Mass extinctions are relatively rare events; however, isolated extinctions of species and clades are quite common, and are a natural part of the evolutionary process.[9] Only recently have extinctions been recorded and scientists have become alarmed at the current high rate of extinctions.[10][11][12][13][14] Most species that become extinct are never scientifically documented. Some scientists estimate that up to half of presently existing plant and animal species may become extinct by 2100.[15] A 2018 report indicated that the phylogenetic diversity of 300 mammalian species erased during the human era since the Late Pleistocene would require 5 to 7 million years to recover.[16]

According to the 2019 Global Assessment Report on Biodiversity and Ecosystem Services by IPBES, the biomass of wild mammals has fallen by 82%, natural ecosystems have lost about half their area and a million species are at risk of extinction—all largely as a result of human actions. Twenty-five percent of plant and animal species are threatened with extinction.[17][18][19] In a subsequent report, IPBES listed unsustainable fishing, hunting and logging as being some of the primary drivers of the global extinction crisis.[20]

In June 2019, one million species of plants and animals were at risk of extinction. At least 571 species have been lost since 1750, but likely many more. The main cause of the extinctions is the destruction of natural habitats by human activities, such as cutting down forests and converting land into fields for farming.[21]

A dagger symbol (†) placed next to the name of a species or other taxon normally indicates its status as extinct.

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Death

Death

Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including the brainstem, and brain death is sometimes used as a legal definition of death. The remains of a former organism normally begin to decompose shortly after death. Death is an inevitable process that eventually occurs in all organisms. Some organisms, such as Turritopsis dohrnii, are biologically immortal. However, they can still die from other means than aging.

Endling

Endling

An endling is the last known individual of a species or subspecies. Once the endling dies, the species becomes extinct. The word was coined in correspondence in the scientific journal Nature. Alternative names put forth for the last individual of its kind include ender and terminarch.

Functional extinction

Functional extinction

Functional extinction is the extinction of a species or other taxon such that:It disappears from the fossil record, or historic reports of its existence cease; The reduced population no longer plays a significant role in ecosystem function; or The population is no longer viable. There are no individuals able to reproduce, or the small population of breeding individuals will not be able to sustain itself due to inbreeding depression and genetic drift, which leads to a loss of fitness.

Fossil

Fossil

A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the fossil record.

Eukaryote

Eukaryote

Eukaryota, whose members are known as eukaryotes, is a diverse domain of organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacteria and Archaea make up the other two domains.

Dinosaur

Dinosaur

Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 245 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is a subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 mya and their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage known to have survived the Cretaceous–Paleogene extinction event approximately 66 mya. Dinosaurs can therefore be divided into avian dinosaurs—birds—and the extinct non-avian dinosaurs, which are all dinosaurs other than birds.

Dodo

Dodo

The dodo is an extinct flightless bird that was endemic to the island of Mauritius, which is east of Madagascar in the Indian Ocean. The dodo's closest genetic relative was the also-extinct Rodrigues solitaire. The two formed the subfamily Raphinae, a clade of extinct flightless birds that were a part of the family which includes pigeons and doves. The closest living relative of the dodo is the Nicobar pigeon. A white dodo was once thought to have existed on the nearby island of Réunion, but it is now believed that this assumption was merely confusion based on the also-extinct Réunion ibis and paintings of white dodos.

Evolution

Evolution

In biology, evolution is the change in heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation tends to exist within any given population as a result of genetic mutation and recombination. Evolution occurs when evolutionary processes such as natural selection and genetic drift act on this variation, resulting in certain characteristics becoming more common or more rare within a population. The evolutionary pressures that determine whether a characteristic is common or rare within a population constantly change, resulting in a change in heritable characteristics arising over successive generations. It is this process of evolution that has given rise to biodiversity at every level of biological organisation.

Ecological niche

Ecological niche

In ecology, a niche is the match of a species to a specific environmental condition. It describes how an organism or population responds to the distribution of resources and competitors and how it in turn alters those same factors. "The type and number of variables comprising the dimensions of an environmental niche vary from one species to another [and] the relative importance of particular environmental variables for a species may vary according to the geographic and biotic contexts".

Competition (biology)

Competition (biology)

Competition is an interaction between organisms or species in which both require a resource that is in limited supply. Competition lowers the fitness of both organisms involved since the presence of one of the organisms always reduces the amount of the resource available to the other.

Extinction event

Extinction event

An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the background extinction rate and the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity.

Dagger (mark)

Dagger (mark)

A dagger, obelisk, or obelus † is a typographical mark that usually indicates a footnote if an asterisk has already been used. The symbol is also used to indicate death or extinction. It is one of the modern descendants of the obelus, a mark used historically by scholars as a critical or highlighting indicator in manuscripts..

Examples

Examples of species and subspecies that are extinct include:

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Dodo

Dodo

The dodo is an extinct flightless bird that was endemic to the island of Mauritius, which is east of Madagascar in the Indian Ocean. The dodo's closest genetic relative was the also-extinct Rodrigues solitaire. The two formed the subfamily Raphinae, a clade of extinct flightless birds that were a part of the family which includes pigeons and doves. The closest living relative of the dodo is the Nicobar pigeon. A white dodo was once thought to have existed on the nearby island of Réunion, but it is now believed that this assumption was merely confusion based on the also-extinct Réunion ibis and paintings of white dodos.

Chinese paddlefish

Chinese paddlefish

The Chinese paddlefish, also known as the Chinese swordfish, is an extinct species of fish that was formerly native to the Yangtze and Yellow River basins in China. With records of specimens over three metres and possibly 7 m (23 ft) in length, it was one of the largest species of freshwater fish. It was the only species in the genus Psephurus and one of two recent species of paddlefish (Polyodontidae), the other being the American paddlefish. It was an anadromous species, meaning that it spent part of its adult life at sea, while migrating upriver to spawn.

Great auk

Great auk

The great auk is a species of flightless alcid that became extinct in the mid-19th century. It was the only modern species in the genus Pinguinus. It is not closely related to the birds now known as penguins, which were discovered later by Europeans and so named by sailors because of their physical resemblance to the great auk.

Hobart Zoo

Hobart Zoo

The Hobart Zoo was an old-fashioned zoological garden located on the Queen's Domain in Hobart, Tasmania, Australia. The Zoo site is very close to the site of the Tasmanian Governor's House, and the Botanical Gardens. Although its location is now primarily the site of a Hobart City Council depot, some remnants and archaeological remains of the original Zoo can still be seen.

Kauaʻi ʻōʻō

Kauaʻi ʻōʻō

The Kauaʻi ʻōʻō or ʻōʻōʻāʻā was the last member of the ʻōʻō (Moho) genus within the Mohoidae family of birds from the islands of Hawaiʻi. The entire family is now extinct. It was previously regarded as a member of the Australo-Pacific honeyeaters.

Mohoidae

Mohoidae

Mohoidae, also known as the Hawaiian honeyeaters, is a family of Hawaiian species of recently extinct, nectarivorous songbirds in the genera Moho (ʻōʻō) and Chaetoptila (kioea). These now extinct birds form their own family, representing the only complete extinction of an entire avian family in modern times, when the disputed family Turnagridae is regarded as invalid. The last surviving species in the family, the Kauai O'o, became extinct after 1987.

Carolina parakeet

Carolina parakeet

The Carolina parakeet, or Carolina conure, is an extinct species of small green neotropical parrot with a bright yellow head, reddish orange face and pale beak that was native to the Eastern, Midwest and Plains states of the United States. It was the only indigenous parrot within its range, as well as one of only three parrot species native to the United States. It was called puzzi la née or pot pot chee by the Seminole and kelinky in Chickasaw. Though formerly prevalent within its range, the bird had become rare by the middle of the 19th century. The last confirmed sighting in the wild was of the ludovicianus subspecies in 1910. The last known specimen, a male named Incas, perished in captivity at the Cincinnati Zoo in 1918, and the species was declared extinct in 1939.

Incas (Carolina parakeet)

Incas (Carolina parakeet)

Incas was a male Carolina parakeet and the last member of his species known with certainty. Though probable sightings of wild Carolina parakeets continued into the 1930s, and the American Ornithologists Union accepted a sighting in 1920, no specimens were collected after 1904 and he is often cited as the last individual in existence. Incas died in the Cincinnati Zoo in 1918, in the same enclosure as Martha, the last passenger pigeon, who died in 1914. He died within one year of his mate, Lady Jane.

Passenger pigeon

Passenger pigeon

The passenger pigeon or wild pigeon is an extinct species of pigeon that was endemic to North America. Its common name is derived from the French word passager, meaning "passing by", due to the migratory habits of the species. The scientific name also refers to its migratory characteristics. The morphologically similar mourning dove was long thought to be its closest relative, and the two were at times confused, but genetic analysis has shown that the genus Patagioenas is more closely related to it than the Zenaida doves.

Martha (passenger pigeon)

Martha (passenger pigeon)

Martha was the last known living passenger pigeon ; she was named "Martha" in honor of the first First Lady Martha Washington.

Schomburgk's deer

Schomburgk's deer

The Schomburgk's deer is an extinct species of deer once endemic to central Thailand. It was described by Edward Blyth in 1863 and named after Sir Robert H. Schomburgk, who was the British consul in Bangkok from 1857 to 1864. It is thought to have gone extinct by 1938, when the last records of the species were published.

Extinct in the wild

Extinct in the wild

A species that is extinct in the wild (EW) is one that has been categorized by the International Union for Conservation of Nature as known only by living members kept in captivity or as a naturalized population outside its historic range due to massive habitat loss.

Definition

External mold of the extinct Lepidodendron from the Upper Carboniferous of Ohio[22][23]
External mold of the extinct Lepidodendron from the Upper Carboniferous of Ohio[22][23]

A species is extinct when the last existing member dies. Extinction therefore becomes a certainty when there are no surviving individuals that can reproduce and create a new generation. A species may become functionally extinct when only a handful of individuals survive, which cannot reproduce due to poor health, age, sparse distribution over a large range, a lack of individuals of both sexes (in sexually reproducing species), or other reasons.

Pinpointing the extinction (or pseudoextinction) of a species requires a clear definition of that species. If it is to be declared extinct, the species in question must be uniquely distinguishable from any ancestor or daughter species, and from any other closely related species. Extinction of a species (or replacement by a daughter species) plays a key role in the punctuated equilibrium hypothesis of Stephen Jay Gould and Niles Eldredge.[24]

Skeleton of various extinct dinosaurs; some other dinosaur lineages still flourish in the form of birds
Skeleton of various extinct dinosaurs; some other dinosaur lineages still flourish in the form of birds

In ecology, extinction is sometimes used informally to refer to local extinction, in which a species ceases to exist in the chosen area of study, despite still existing elsewhere. Local extinctions may be made good by the reintroduction of individuals of that species taken from other locations; wolf reintroduction is an example of this. Species that are not globally extinct are termed extant. Those species that are extant, yet are threatened with extinction, are referred to as threatened or endangered species.

The dodo of Mauritius, shown here in a 1626 illustration by Roelant Savery, is an often-cited example of modern extinction.[25]
The dodo of Mauritius, shown here in a 1626 illustration by Roelant Savery, is an often-cited example of modern extinction.[25]

Currently, an important aspect of extinction is human attempts to preserve critically endangered species. These are reflected by the creation of the conservation status "extinct in the wild" (EW). Species listed under this status by the International Union for Conservation of Nature (IUCN) are not known to have any living specimens in the wild and are maintained only in zoos or other artificial environments. Some of these species are functionally extinct, as they are no longer part of their natural habitat and it is unlikely the species will ever be restored to the wild.[26] When possible, modern zoological institutions try to maintain a viable population for species preservation and possible future reintroduction to the wild, through use of carefully planned breeding programs.

The extinction of one species' wild population can have knock-on effects, causing further extinctions. These are also called "chains of extinction".[27] This is especially common with extinction of keystone species.

A 2018 study indicated that the sixth mass extinction started in the Late Pleistocene could take up to 5 to 7 million years to restore 2.5 billion years of unique mammal diversity to what it was before the human era.[16][28]

Pseudoextinction

Extinction of a parent species where daughter species or subspecies are still extant is called pseudoextinction or phyletic extinction. Effectively, the old taxon vanishes, transformed (anagenesis) into a successor,[29] or split into more than one (cladogenesis).[30]

Pseudoextinction is difficult to demonstrate unless one has a strong chain of evidence linking a living species to members of a pre-existing species. For example, it is sometimes claimed that the extinct Hyracotherium, which was an early horse that shares a common ancestor with the modern horse, is pseudoextinct, rather than extinct, because there are several extant species of Equus, including zebra and donkey; however, as fossil species typically leave no genetic material behind, one cannot say whether Hyracotherium evolved into more modern horse species or merely evolved from a common ancestor with modern horses. Pseudoextinction is much easier to demonstrate for larger taxonomic groups.

Lazarus taxa

The coelacanth, a fish related to lungfish and tetrapods, was considered to have been extinct since the end of the Cretaceous Period. In 1938, however, a living specimen was found off the Chalumna River (now Tyolomnqa) on the east coast of South Africa.[31] Museum curator Marjorie Courtenay-Latimer discovered the fish among the catch of a local trawler operated by Captain Hendrick Goosen, on December 23, 1938.[31] A local chemistry professor, JLB Smith, confirmed the fish's importance with a famous cable: "MOST IMPORTANT PRESERVE SKELETON AND GILLS = FISH DESCRIBED".[31]

Far more recent possible or presumed extinctions of species which may turn out still to exist include the thylacine, or Tasmanian tiger (Thylacinus cynocephalus), the last known example of which died in Hobart Zoo in Tasmania in 1936; the Japanese wolf (Canis lupus hodophilax), last sighted over 100 years ago; the American ivory-billed woodpecker (Campephilus principalis), with the last universally accepted sighting in 1944; and the slender-billed curlew (Numenius tenuirostris), not seen since 2007.[32]

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Lepidodendron

Lepidodendron

Lepidodendron is an extinct genus of primitive vascular plants belonging to order Lepidodendrales, part of a group of Lycopodiopsida known as scale trees or arborescent lycophytes, related to quillworts and lycopsids. They were part of the coal forest flora. They sometimes reached heights of 50 metres, and the trunks were often over 1 m (3.3 ft) in diameter. They thrived during the Carboniferous Period. Sometimes erroneously called "giant club mosses", the genus was actually more closely related to modern quillworts than to modern club mosses. Within the form classification system used within paleobotany, Lepidodendron is both used for the whole plant as well as specifically the stems and leaves.

Ohio

Ohio

Ohio, officially the State of Ohio is a state in the Midwestern United States. Of the fifty U.S. states, it is the 34th-largest by area. With a population of nearly 11.8 million, Ohio is the seventh-most populous and tenth-most densely populated state. Its capital and largest city is Columbus, with the Columbus metro area, Greater Cincinnati, and Greater Cleveland being the largest metropolitan areas. Ohio is bordered by Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the west, and Michigan to the northwest. Ohio is nicknamed the "Buckeye State" after its Ohio buckeye trees, and Ohioans are also known as "Buckeyes". Its state flag is the only non-rectangular flag of all the U.S. states.

Functional extinction

Functional extinction

Functional extinction is the extinction of a species or other taxon such that:It disappears from the fossil record, or historic reports of its existence cease; The reduced population no longer plays a significant role in ecosystem function; or The population is no longer viable. There are no individuals able to reproduce, or the small population of breeding individuals will not be able to sustain itself due to inbreeding depression and genetic drift, which leads to a loss of fitness.

Pseudoextinction

Pseudoextinction

Pseudoextinction of a species occurs when all members of the species are extinct, but members of a daughter species remain alive. The term pseudoextinction refers to the evolution of a species into a new form, with the resultant disappearance of the ancestral form. Pseudoextinction results in the relationship between ancestor and descendant still existing even though the ancestor species no longer exists.

Punctuated equilibrium

Punctuated equilibrium

In evolutionary biology, punctuated equilibrium is a theory that proposes that once a species appears in the fossil record, the population will become stable, showing little evolutionary change for most of its geological history. This state of little or no morphological change is called stasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and geologically rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which a species splits into two distinct species, rather than one species gradually transforming into another.

Niles Eldredge

Niles Eldredge

Niles Eldredge is an American biologist and paleontologist, who, along with Stephen Jay Gould, proposed the theory of punctuated equilibrium in 1972.

Dinosaur

Dinosaur

Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 245 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is a subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 mya and their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage known to have survived the Cretaceous–Paleogene extinction event approximately 66 mya. Dinosaurs can therefore be divided into avian dinosaurs—birds—and the extinct non-avian dinosaurs, which are all dinosaurs other than birds.

Ecology

Ecology

Ecology is the study of the relationships among living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps with the closely related sciences of biogeography, evolutionary biology, genetics, ethology, and natural history. Ecology is a branch of biology, and it is not synonymous with environmentalism.

Local extinction

Local extinction

Local extinction, also extirpation, is the termination of a species in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinctions.

Endangered species

Endangered species

An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and invasive species. The International Union for Conservation of Nature (IUCN) Red List lists the global conservation status of many species, and various other agencies assess the status of species within particular areas. Many nations have laws that protect conservation-reliant species which, for example, forbid hunting, restrict land development, or create protected areas. Some endangered species are the target of extensive conservation efforts such as captive breeding and habitat restoration.

Dodo

Dodo

The dodo is an extinct flightless bird that was endemic to the island of Mauritius, which is east of Madagascar in the Indian Ocean. The dodo's closest genetic relative was the also-extinct Rodrigues solitaire. The two formed the subfamily Raphinae, a clade of extinct flightless birds that were a part of the family which includes pigeons and doves. The closest living relative of the dodo is the Nicobar pigeon. A white dodo was once thought to have existed on the nearby island of Réunion, but it is now believed that this assumption was merely confusion based on the also-extinct Réunion ibis and paintings of white dodos.

Mauritius

Mauritius

Mauritius, officially the Republic of Mauritius, is an island nation in the Indian Ocean about 2,000 kilometres off the southeast coast of the African continent, east of Madagascar. It includes the main island, as well as Rodrigues, Agaléga and St. Brandon. The islands of Mauritius and Rodrigues, along with nearby Réunion, are part of the Mascarene Islands. The main island of Mauritius, where most of the population is concentrated, hosts the capital and largest city, Port Louis. The country spans 2,040 square kilometres (790 sq mi) and has an exclusive economic zone covering 2,300,000 square kilometres.

Causes

The passenger pigeon, one of the hundreds of species of extinct birds, was hunted to extinction over the course of a few decades.
The passenger pigeon, one of the hundreds of species of extinct birds, was hunted to extinction over the course of a few decades.

As long as species have been evolving, species have been going extinct. It is estimated that over 99.9% of all species that ever lived are extinct. The average lifespan of a species is 1–10 million years,[33] although this varies widely between taxa. A variety of causes can contribute directly or indirectly to the extinction of a species or group of species. "Just as each species is unique", write Beverly and Stephen C. Stearns, "so is each extinction ... the causes for each are varied—some subtle and complex, others obvious and simple".[34] Most simply, any species that cannot survive and reproduce in its environment and cannot move to a new environment where it can do so, dies out and becomes extinct. Extinction of a species may come suddenly when an otherwise healthy species is wiped out completely, as when toxic pollution renders its entire habitat unliveable; or may occur gradually over thousands or millions of years, such as when a species gradually loses out in competition for food to better adapted competitors. Extinction may occur a long time after the events that set it in motion, a phenomenon known as extinction debt.

Assessing the relative importance of genetic factors compared to environmental ones as the causes of extinction has been compared to the debate on nature and nurture.[35] The question of whether more extinctions in the fossil record have been caused by evolution or by competition or by predation or by disease or by catastrophe is a subject of discussion; Mark Newman, the author of Modeling Extinction, argues for a mathematical model that falls in all positions.[5] By contrast, conservation biology uses the extinction vortex model to classify extinctions by cause. When concerns about human extinction have been raised, for example in Sir Martin Rees' 2003 book Our Final Hour, those concerns lie with the effects of climate change or technological disaster.

Human-driven extinction started as humans migrated out of Africa more than 60,000 years ago.[36] Currently, environmental groups and some governments are concerned with the extinction of species caused by humanity, and they try to prevent further extinctions through a variety of conservation programs.[10] Humans can cause extinction of a species through overharvesting, pollution, habitat destruction, introduction of invasive species (such as new predators and food competitors), overhunting, and other influences. Explosive, unsustainable human population growth and increasing per capita consumption are essential drivers of the extinction crisis.[37][38][39][40] According to the International Union for Conservation of Nature (IUCN), 784 extinctions have been recorded since the year 1500, the arbitrary date selected to define "recent" extinctions, up to the year 2004; with many more likely to have gone unnoticed. Several species have also been listed as extinct since 2004.[41]

Genetics and demographic phenomena

If adaptation increasing population fitness is slower than environmental degradation plus the accumulation of slightly deleterious mutations, then a population will go extinct.[42] Smaller populations have fewer beneficial mutations entering the population each generation, slowing adaptation. It is also easier for slightly deleterious mutations to fix in small populations; the resulting positive feedback loop between small population size and low fitness can cause mutational meltdown.

Limited geographic range is the most important determinant of genus extinction at background rates but becomes increasingly irrelevant as mass extinction arises.[43] Limited geographic range is a cause both of small population size and of greater vulnerability to local environmental catastrophes.

Extinction rates can be affected not just by population size, but by any factor that affects evolvability, including balancing selection, cryptic genetic variation, phenotypic plasticity, and robustness. A diverse or deep gene pool gives a population a higher chance in the short term of surviving an adverse change in conditions. Effects that cause or reward a loss in genetic diversity can increase the chances of extinction of a species. Population bottlenecks can dramatically reduce genetic diversity by severely limiting the number of reproducing individuals and make inbreeding more frequent.

Genetic pollution

Extinction sometimes results for species evolved to specific ecologies[44] that are subjected to genetic pollution—i.e., uncontrolled hybridization, introgression and genetic swamping that lead to homogenization or out-competition from the introduced (or hybrid) species.[45] Endemic populations can face such extinctions when new populations are imported or selectively bred by people, or when habitat modification brings previously isolated species into contact. Extinction is likeliest for rare species coming into contact with more abundant ones;[46] interbreeding can swamp the rarer gene pool and create hybrids, depleting the purebred gene pool (for example, the endangered wild water buffalo is most threatened with extinction by genetic pollution from the abundant domestic water buffalo). Such extinctions are not always apparent from morphological (non-genetic) observations. Some degree of gene flow is a normal evolutionary process; nevertheless, hybridization (with or without introgression) threatens rare species' existence.[47][48]

The gene pool of a species or a population is the variety of genetic information in its living members. A large gene pool (extensive genetic diversity) is associated with robust populations that can survive bouts of intense selection. Meanwhile, low genetic diversity (see inbreeding and population bottlenecks) reduces the range of adaptions possible.[49] Replacing native with alien genes narrows genetic diversity within the original population,[46][50] thereby increasing the chance of extinction.

Scorched land resulting from slash-and-burn agriculture
Scorched land resulting from slash-and-burn agriculture

Habitat degradation

Habitat degradation is currently the main anthropogenic cause of species extinctions. The main cause of habitat degradation worldwide is agriculture, with urban sprawl, logging, mining, and some fishing practices close behind. The degradation of a species' habitat may alter the fitness landscape to such an extent that the species is no longer able to survive and becomes extinct. This may occur by direct effects, such as the environment becoming toxic, or indirectly, by limiting a species' ability to compete effectively for diminished resources or against new competitor species.

Habitat degradation through toxicity can kill off a species very rapidly, by killing all living members through contamination or sterilizing them. It can also occur over longer periods at lower toxicity levels by affecting life span, reproductive capacity, or competitiveness.

Habitat degradation can also take the form of a physical destruction of niche habitats. The widespread destruction of tropical rainforests and replacement with open pastureland is widely cited as an example of this;[15] elimination of the dense forest eliminated the infrastructure needed by many species to survive. For example, a fern that depends on dense shade for protection from direct sunlight can no longer survive without forest to shelter it. Another example is the destruction of ocean floors by bottom trawling.[51]

Diminished resources or introduction of new competitor species also often accompany habitat degradation. Global warming has allowed some species to expand their range, bringing unwelcome competition to other species that previously occupied that area. Sometimes these new competitors are predators and directly affect prey species, while at other times they may merely outcompete vulnerable species for limited resources. Vital resources including water and food can also be limited during habitat degradation, leading to extinction.

The golden toad was last seen on May 15, 1989. Decline in amphibian populations is ongoing worldwide.
The golden toad was last seen on May 15, 1989. Decline in amphibian populations is ongoing worldwide.

Predation, competition, and disease

In the natural course of events, species become extinct for a number of reasons, including but not limited to: extinction of a necessary host, prey or pollinator, inter-species competition, inability to deal with evolving diseases and changing environmental conditions (particularly sudden changes) which can act to introduce novel predators, or to remove prey. Recently in geological time, humans have become an additional cause of extinction (some people would say premature extinction) of some species, either as a new mega-predator or by transporting animals and plants from one part of the world to another. Such introductions have been occurring for thousands of years, sometimes intentionally (e.g. livestock released by sailors on islands as a future source of food) and sometimes accidentally (e.g. rats escaping from boats). In most cases, the introductions are unsuccessful, but when an invasive alien species does become established, the consequences can be catastrophic. Invasive alien species can affect native species directly by eating them, competing with them, and introducing pathogens or parasites that sicken or kill them; or indirectly by destroying or degrading their habitat. Human populations may themselves act as invasive predators. According to the "overkill hypothesis", the swift extinction of the megafauna in areas such as Australia (40,000 years before present), North and South America (12,000 years before present), Madagascar, Hawaii (AD 300–1000), and New Zealand (AD 1300–1500), resulted from the sudden introduction of human beings to environments full of animals that had never seen them before and were therefore completely unadapted to their predation techniques.[52]

Coextinction

The large Haast's eagle and moa from New Zealand
The large Haast's eagle and moa from New Zealand

Coextinction refers to the loss of a species due to the extinction of another; for example, the extinction of parasitic insects following the loss of their hosts. Coextinction can also occur when a species loses its pollinator, or to predators in a food chain who lose their prey. "Species coextinction is a manifestation of one of the interconnectednesses of organisms in complex ecosystems ... While coextinction may not be the most important cause of species extinctions, it is certainly an insidious one."[53] Coextinction is especially common when a keystone species goes extinct. Models suggest that coextinction is the most common form of biodiversity loss. There may be a cascade of coextinction across the trophic levels. Such effects are most severe in mutualistic and parasitic relationships. An example of coextinction is the Haast's eagle and the moa: the Haast's eagle was a predator that became extinct because its food source became extinct. The moa were several species of flightless birds that were a food source for the Haast's eagle.[54]

Climate change

Extinction as a result of climate change has been confirmed by fossil studies.[55] Particularly, the extinction of amphibians during the Carboniferous Rainforest Collapse, 305 million years ago.[55] A 2003 review across 14 biodiversity research centers predicted that, because of climate change, 15–37% of land species would be "committed to extinction" by 2050.[56][57] The ecologically rich areas that would potentially suffer the heaviest losses include the Cape Floristic Region and the Caribbean Basin. These areas might see a doubling of present carbon dioxide levels and rising temperatures that could eliminate 56,000 plant and 3,700 animal species.[58] Climate change has also been found to be a factor in habitat loss and desertification.[59]

Sexual selection and male investment

Studies of fossils following species from the time they evolved to their extinction show that species with high sexual dimorphism, especially characteristics in males that are used to compete for mating, are at a higher risk of extinction and die out faster than less sexually dimorphic species, the least sexually dimorphic species surviving for millions of years while the most sexually dimorphic species die out within mere thousands of years. Earlier studies based on counting the number of currently living species in modern taxa have shown a higher number of species in more sexually dimorphic taxa which have been interpreted as higher survival in taxa with more sexual selection, but such studies of modern species only measure indirect effects of extinction and are subject to error sources such as dying and doomed taxa speciating more due to splitting of habitat ranges into more small isolated groups during the habitat retreat of taxa approaching extinction. Possible causes of the higher extinction risk in species with more sexual selection shown by the comprehensive fossil studies that rule out such error sources include expensive sexually selected ornaments having negative effects on the ability to survive natural selection, as well as sexual selection removing a diversity of genes that under current ecological conditions are neutral for natural selection but some of which may be important for surviving climate change.[60]

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Passenger pigeon

Passenger pigeon

The passenger pigeon or wild pigeon is an extinct species of pigeon that was endemic to North America. Its common name is derived from the French word passager, meaning "passing by", due to the migratory habits of the species. The scientific name also refers to its migratory characteristics. The morphologically similar mourning dove was long thought to be its closest relative, and the two were at times confused, but genetic analysis has shown that the genus Patagioenas is more closely related to it than the Zenaida doves.

Habitat

Habitat

In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical manifestation of its ecological niche. Thus "habitat" is a species-specific term, fundamentally different from concepts such as environment or vegetation assemblages, for which the term "habitat-type" is more appropriate.

Extinction debt

Extinction debt

In ecology, extinction debt is the future extinction of species due to events in the past. The phrases dead clade walking and survival without recovery express the same idea.

Fossil

Fossil

A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the fossil record.

Evolution

Evolution

In biology, evolution is the change in heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation tends to exist within any given population as a result of genetic mutation and recombination. Evolution occurs when evolutionary processes such as natural selection and genetic drift act on this variation, resulting in certain characteristics becoming more common or more rare within a population. The evolutionary pressures that determine whether a characteristic is common or rare within a population constantly change, resulting in a change in heritable characteristics arising over successive generations. It is this process of evolution that has given rise to biodiversity at every level of biological organisation.

Conservation biology

Conservation biology

Conservation biology is the study of the conservation of nature and of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions. It is an interdisciplinary subject drawing on natural and social sciences, and the practice of natural resource management.

Extinction vortex

Extinction vortex

Extinction vortices are a class of models through which conservation biologists, geneticists and ecologists can understand the dynamics of and categorize extinctions in the context of their causes. This model shows the events that ultimately lead small populations to become increasingly vulnerable as they spiral toward extinction. Developed by M. E. Gilpin and M. E. Soulé in 1986, there are currently four classes of extinction vortices. The first two deal with environmental factors that have an effect on the ecosystem or community level, such as disturbance, pollution, habitat loss etc. Whereas the second two deal with genetic factors such as inbreeding depression and outbreeding depression, genetic drift etc.

Human extinction

Human extinction

Human extinction is the hypothetical end of the human species due to either natural causes such as population decline from sub-replacement fertility, an asteroid impact, large-scale volcanism, or to anthropogenic (human) causes.

Martin Rees

Martin Rees

Martin John Rees, Baron Rees of Ludlow is a British cosmologist and astrophysicist. He is the fifteenth Astronomer Royal, appointed in 1995, and was Master of Trinity College, Cambridge, from 2004 to 2012 and President of the Royal Society between 2005 and 2010.

Our Final Hour

Our Final Hour

Our Final Hour is a 2003 book by the British Astronomer Royal Sir Martin Rees. The full title of the book is Our Final Hour: A Scientist's Warning: How Terror, Error, and Environmental Disaster Threaten Humankind's Future In This Century—On Earth and Beyond. It was published in the United Kingdom under the title Our Final Century: Will the Human Race Survive the Twenty-first Century?.

Climate change

Climate change

In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to Earth's climate. The current rise in global average temperature is more rapid than previous changes, and is primarily caused by humans burning fossil fuels. Fossil fuel use, deforestation, and some agricultural and industrial practices increase greenhouse gases, notably carbon dioxide and methane. Greenhouse gases absorb some of the heat that the Earth radiates after it warms from sunlight. Larger amounts of these gases trap more heat in Earth's lower atmosphere, causing global warming.

Conservation movement

Conservation movement

The conservation movement, also known as nature conservation, is a political, environmental, and social movement that seeks to manage and protect natural resources, including animal, fungus, and plant species as well as their habitat for the future. Conservationists are concerned with leaving the environment in a better state than the condition they found it in. Evidence-based conservation seeks to use high quality scientific evidence to make conservation efforts more effective.

Mass extinctions

Marine extinction intensity during the Phanerozoic
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Millions of years ago
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K–Pg
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P–Tr
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Late D
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The blue graph shows the apparent percentage (not the absolute number) of marine animal genera becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized. The labels of the traditional "Big Five" extinction events and the more recently recognised Capitanian mass extinction event are clickable links; see Extinction event for more details. (source and image info)CambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleogeneNeogene
Marine extinction intensity during the Phanerozoic
%
Millions of years ago
Marine extinction intensity during the Phanerozoic
.mw-parser-output .tooltip-dotted{border-bottom:1px dotted;cursor:help}%
Millions of years ago
(H)
K–Pg
Tr–J
P–Tr
Cap
Late D
O–S



The blue graph shows the apparent percentage (not the absolute number) of marine animal genera becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized. The labels of the traditional "Big Five" extinction events and the more recently recognised Capitanian mass extinction event are clickable links; see Extinction event for more details. (source and image info)CambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleogeneNeogene
The blue graph shows the apparent percentage (not the absolute number) of marine animal genera becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized. The labels of the traditional "Big Five" extinction events and the more recently recognised Capitanian mass extinction event are clickable links; see Extinction event for more details. (source and image info)

There have been at least five mass extinctions in the history of life on earth, and four in the last 350 million years in which many species have disappeared in a relatively short period of geological time. A massive eruptive event that released large quantities of tephra particles into the atmosphere is considered to be one likely cause of the "Permian–Triassic extinction event" about 250 million years ago,[61] which is estimated to have killed 90% of species then existing.[62] There is also evidence to suggest that this event was preceded by another mass extinction, known as Olson's Extinction.[61] The Cretaceous–Paleogene extinction event (K–Pg) occurred 66 million years ago, at the end of the Cretaceous period; it is best known for having wiped out non-avian dinosaurs, among many other species.

Modern extinctions

The changing distribution of the world's land mammals in tonnes of carbon. The biomass of wild land mammals has declined by 85% since the emergence of humans
The changing distribution of the world's land mammals in tonnes of carbon. The biomass of wild land mammals has declined by 85% since the emergence of humans

According to a 1998 survey of 400 biologists conducted by New York's American Museum of Natural History, nearly 70% believed that the Earth is currently in the early stages of a human-caused mass extinction,[63] known as the Holocene extinction. In that survey, the same proportion of respondents agreed with the prediction that up to 20% of all living populations could become extinct within 30 years (by 2028). A 2014 special edition of Science declared there is widespread consensus on the issue of human-driven mass species extinctions.[64] A 2020 study published in PNAS stated that the contemporary extinction crisis "may be the most serious environmental threat to the persistence of civilization, because it is irreversible."[65]

Biologist E. O. Wilson estimated[15] in 2002 that if current rates of human destruction of the biosphere continue, one-half of all plant and animal species of life on earth will be extinct in 100 years.[66] More significantly, the current rate of global species extinctions is estimated as 100 to 1,000 times "background" rates (the average extinction rates in the evolutionary time scale of planet Earth),[67][68] faster than at any other time in human history,[69][70] while future rates are likely 10,000 times higher.[68] However, some groups are going extinct much faster. Biologists Paul R. Ehrlich and Stuart Pimm, among others, contend that human population growth and overconsumption are the main drivers of the modern extinction crisis.[71][72][37][73]

In January 2020, the UN's Convention on Biological Diversity drafted a plan to mitigate the contemporary extinction crisis by establishing a deadline of 2030 to protect 30% of the earth's land and oceans and reduce pollution by 50%, with the goal of allowing for the restoration of ecosystems by 2050.[74][75] The 2020 United Nations' Global Biodiversity Outlook report stated that of the 20 biodiversity goals laid out by the Aichi Biodiversity Targets in 2010, only 6 were "partially achieved" by the deadline of 2020.[76] The report warned that biodiversity will continue to decline if the status quo is not changed, in particular the "currently unsustainable patterns of production and consumption, population growth and technological developments".[77] In a 2021 report published in the journal Frontiers in Conservation Science, some top scientists asserted that even if the Aichi Biodiversity Targets set for 2020 had been achieved, it would not have resulted in a significant mitigation of biodiversity loss. They added that failure of the global community to reach these targets is hardly surprising given that biodiversity loss is "nowhere close to the top of any country's priorities, trailing far behind other concerns such as employment, healthcare, economic growth, or currency stability."[78][79]

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Extinction event

Extinction event

An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the background extinction rate and the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity.

Holocene extinction

Holocene extinction

The Holocene extinction, or Anthropocene extinction, is the ongoing extinction event during the Holocene epoch. The extinctions span numerous families of plants and animals, including mammals, birds, reptiles, amphibians, fish, invertebrates, and affecting not just terrestrial species but also large sectors of marine life. With widespread degradation of biodiversity hotspots, such as coral reefs and rainforests, as well as other areas, the vast majority of these extinctions are thought to be undocumented, as the species are undiscovered at the time of their extinction, which goes unrecorded. The current rate of extinction of species is estimated at 100 to 1,000 times higher than natural background extinction rates, and is increasing.

Cretaceous–Paleogene extinction event

Cretaceous–Paleogene extinction event

The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary (K–T) extinction, was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. The event caused the extinction of all non-avian dinosaurs. Most other tetrapods weighing more than 25 kilograms also became extinct, with the exception of some ectothermic species such as sea turtles and crocodilians. It marked the end of the Cretaceous Period, and with it the Mesozoic era, while heralding the beginning of the Cenozoic era, which continues to this day.

Permian–Triassic extinction event

Permian–Triassic extinction event

The Permian–Triassic extinction event, also known as the End-Permian extinction event and colloquially as the Great Dying, forms the boundary between the Permian and Triassic geologic periods, and with them the Paleozoic and Mesozoic eras respectively, approximately 251.9 million years ago. As the largest of the "Big Five" mass extinctions of the Phanerozoic, it is the Earth's most severe known extinction event, with the extinction of 57% of biological families, 83% of genera, 81% of marine species and 70% of terrestrial vertebrate species. It is the largest known mass extinction of insects. There is evidence for one to three distinct pulses, or phases, of extinction.

Capitanian mass extinction event

Capitanian mass extinction event

The Capitanian mass extinction event, also known as the end-Guadalupian extinction event, the Guadalupian-Lopingian boundary mass extinction, or the pre-Lopingian crisis was an extinction event that predated the end-Permian extinction event. The mass extinction occurred during a period of decreased species richness and increased extinction rates near the end of the Middle Permian, also known as the Guadalupian epoch. It is often called the end-Guadalupian extinction event because of its initial recognition between the Guadalupian and Lopingian series; however, more refined stratigraphic study suggests that extinction peaks in many taxonomic groups occurred within the Guadalupian, in the latter half of the Capitanian age. The extinction event has been argued to have begun around 262 million years ago with the Late Guadalupian crisis, though its most intense pulse occurred 259 million years ago in what is known as the Guadalupian-Lopingian boundary event.

Late Devonian extinction

Late Devonian extinction

The Late Devonian extinction consisted of several extinction events in the Late Devonian Epoch, which collectively represent one of the five largest mass extinction events in the history of life on Earth. The term primarily refers to a major extinction, the Kellwasser event, also known as the Frasnian-Famennian extinction, which occurred around 372 million years ago, at the boundary between the Frasnian stage and the Famennian stage, the last stage in the Devonian Period. Overall, 19% of all families and 50% of all genera became extinct. A second mass extinction called the Hangenberg event, also known as the end-Devonian extinction, occurred 359 million years ago, bringing an end to the Famennian and Devonian, as the world transitioned into the Carboniferous Period.

Late Ordovician mass extinction

Late Ordovician mass extinction

The Late Ordovician mass extinction (LOME), sometimes known as the end-Ordovician mass extinction or the Ordovician-Silurian extinction, is the first of the "big five" major mass extinction events in Earth's history, occurring roughly 443 Mya. It is often considered to be the second-largest known extinction event, in terms of the percentage of genera that became extinct. Extinction was global during this interval, eliminating 49–60% of marine genera and nearly 85% of marine species. Under most tabulations, only the Permian-Triassic mass extinction exceeds the Late Ordovician mass extinction in biodiversity loss. The extinction event abruptly affected all major taxonomic groups and caused the disappearance of one third of all brachiopod and bryozoan families, as well as numerous groups of conodonts, trilobites, echinoderms, corals, bivalves, and graptolites. Despite its taxonomic severity, the Late Ordovician mass extinction did not produce major changes to ecosystem structures compared to other mass extinctions, nor did it lead to any particular morphological innovations. Diversity gradually recovered to pre-extinction levels over the first 5 million years of the Silurian Period.

Animal

Animal

Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 micrometres (0.00033 in) to 33.6 metres (110 ft). They have complex interactions with each other and their environments, forming intricate food webs. The scientific study of animals is known as zoology.

Genus

Genus

Genus is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.E.g. Panthera leo (lion) and Panthera onca (jaguar) are two species within the genus Panthera. Panthera is a genus within the family Felidae.

Olson's Extinction

Olson's Extinction

Olson's Extinction was a mass extinction that occurred 273 million years ago in the late Cisuralian or early Guadalupian of the Permian period and which predated the Permian–Triassic extinction event. It is named after Everett C. Olson. There was a sudden change between the early Permian and middle/late Permian faunas. Some authors also place a hiatus in the continental fossil record around that time, but others disagree. Since then this event has been realized across many groups, including plants, marine invertebrates, and tetrapods.

Cretaceous

Cretaceous

The Cretaceous is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation Kreide.

Dinosaur

Dinosaur

Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 245 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is a subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 mya and their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage known to have survived the Cretaceous–Paleogene extinction event approximately 66 mya. Dinosaurs can therefore be divided into avian dinosaurs—birds—and the extinct non-avian dinosaurs, which are all dinosaurs other than birds.

History of scientific understanding

Tyrannosaurus, one of the many extinct dinosaur genera. The cause of the Cretaceous–Paleogene extinction event is a subject of much debate amongst researchers.
Tyrannosaurus, one of the many extinct dinosaur genera. The cause of the Cretaceous–Paleogene extinction event is a subject of much debate amongst researchers.
Georges Cuvier compared fossil mammoth jaws to those of living elephants, concluding that they were distinct from any known living species.[80]
Georges Cuvier compared fossil mammoth jaws to those of living elephants, concluding that they were distinct from any known living species.[80]

For much of history, the modern understanding of extinction as the end of a species was incompatible with the prevailing worldview. Prior to the 19th century, much of Western society adhered to the belief that the world was created by God and as such was complete and perfect.[81] This concept reached its heyday in the 1700s with the peak popularity of a theological concept called the great chain of being, in which all life on earth, from the tiniest microorganism to God, is linked in a continuous chain.[82] The extinction of a species was impossible under this model, as it would create gaps or missing links in the chain and destroy the natural order.[81][82] Thomas Jefferson was a firm supporter of the great chain of being and an opponent of extinction,[81][83] famously denying the extinction of the woolly mammoth on the grounds that nature never allows a race of animals to become extinct.[84]

A series of fossils were discovered in the late 17th century that appeared unlike any living species. As a result, the scientific community embarked on a voyage of creative rationalization, seeking to understand what had happened to these species within a framework that did not account for total extinction. In October 1686, Robert Hooke presented an impression of a nautilus to the Royal Society that was more than two feet in diameter,[85] and morphologically distinct from any known living species. Hooke theorized that this was simply because the species lived in the deep ocean and no one had discovered them yet.[82] While he contended that it was possible a species could be "lost", he thought this highly unlikely.[82] Similarly, in 1695, Sir Thomas Molyneux published an account of enormous antlers found in Ireland that did not belong to any extant taxa in that area.[83][86] Molyneux reasoned that they came from the North American moose and that the animal had once been common on the British Isles.[83][86] Rather than suggest that this indicated the possibility of species going extinct, he argued that although organisms could become locally extinct, they could never be entirely lost and would continue to exist in some unknown region of the globe.[86] The antlers were later confirmed to be from the extinct deer Megaloceros.[83] Hooke and Molyneux's line of thinking was difficult to disprove. When parts of the world had not been thoroughly examined and charted, scientists could not rule out that animals found only in the fossil record were not simply "hiding" in unexplored regions of the Earth.[87]

Georges Cuvier is credited with establishing the modern conception of extinction in a 1796 lecture to the French Institute,[80][84] though he would spend most of his career trying to convince the wider scientific community of his theory.[88] Cuvier was a well-regarded geologist, lauded for his ability to reconstruct the anatomy of an unknown species from a few fragments of bone.[80] His primary evidence for extinction came from mammoth skulls found in the Paris basin.[80] Cuvier recognized them as distinct from any known living species of elephant, and argued that it was highly unlikely such an enormous animal would go undiscovered.[80] In 1812, Cuvier, along with Alexandre Brongniart and Geoffroy Saint-Hilaire, mapped the strata of the Paris basin.[82] They saw alternating saltwater and freshwater deposits, as well as patterns of the appearance and disappearance of fossils throughout the record.[83][88] From these patterns, Cuvier inferred historic cycles of catastrophic flooding, extinction, and repopulation of the earth with new species.[83][88]

Cuvier's fossil evidence showed that very different life forms existed in the past than those that exist today, a fact that was accepted by most scientists.[81] The primary debate focused on whether this turnover caused by extinction was gradual or abrupt in nature.[88] Cuvier understood extinction to be the result of cataclysmic events that wipe out huge numbers of species, as opposed to the gradual decline of a species over time.[89] His catastrophic view of the nature of extinction garnered him many opponents in the newly emerging school of uniformitarianism.[89]

Jean-Baptiste Lamarck, a gradualist and colleague of Cuvier, saw the fossils of different life forms as evidence of the mutable character of species.[88] While Lamarck did not deny the possibility of extinction, he believed that it was exceptional and rare and that most of the change in species over time was due to gradual change.[88] Unlike Cuvier, Lamarck was skeptical that catastrophic events of a scale large enough to cause total extinction were possible. In his geological history of the earth titled Hydrogeologie, Lamarck instead argued that the surface of the earth was shaped by gradual erosion and deposition by water, and that species changed over time in response to the changing environment.[88][90]

Charles Lyell, a noted geologist and founder of uniformitarianism, believed that past processes should be understood using present day processes. Like Lamarck, Lyell acknowledged that extinction could occur, noting the total extinction of the dodo and the extirpation of indigenous horses to the British Isles.[82] He similarly argued against mass extinctions, believing that any extinction must be a gradual process.[80][84] Lyell also showed that Cuvier's original interpretation of the Parisian strata was incorrect. Instead of the catastrophic floods inferred by Cuvier, Lyell demonstrated that patterns of saltwater and freshwater deposits, like those seen in the Paris basin, could be formed by a slow rise and fall of sea levels.[83]

The concept of extinction was integral to Charles Darwin's On the Origin of Species, with less fit lineages disappearing over time. For Darwin, extinction was a constant side effect of competition.[91] Because of the wide reach of On the Origin of Species, it was widely accepted that extinction occurred gradually and evenly (a concept now referred to as background extinction).[84] It was not until 1982, when David Raup and Jack Sepkoski published their seminal paper on mass extinctions, that Cuvier was vindicated and catastrophic extinction was accepted as an important mechanism. The current understanding of extinction is a synthesis of the cataclysmic extinction events proposed by Cuvier, and the background extinction events proposed by Lyell and Darwin.

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Cretaceous–Paleogene extinction event

Cretaceous–Paleogene extinction event

The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary (K–T) extinction, was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. The event caused the extinction of all non-avian dinosaurs. Most other tetrapods weighing more than 25 kilograms also became extinct, with the exception of some ectothermic species such as sea turtles and crocodilians. It marked the end of the Cretaceous Period, and with it the Mesozoic era, while heralding the beginning of the Cenozoic era, which continues to this day.

Georges Cuvier

Georges Cuvier

Jean Léopold Nicolas Frédéric, Baron Cuvier, known as Georges Cuvier, was a French naturalist and zoologist, sometimes referred to as the "founding father of paleontology". Cuvier was a major figure in natural sciences research in the early 19th century and was instrumental in establishing the fields of comparative anatomy and paleontology through his work in comparing living animals with fossils.

Mammoth

Mammoth

A mammoth is any species of the extinct elephantid genus Mammuthus, one of the many genera that make up the order of trunked mammals called proboscideans. The various species of mammoth were commonly equipped with long, curved tusks and, in northern species, a covering of long hair. They lived from the Pliocene epoch into the Holocene at about 4,000 years ago, and various species existed in Africa, Europe, Asia, and North America. They were members of the family Elephantidae, which also contains the two genera of modern elephants and their ancestors. Mammoths are more closely related to living Asian elephants than African elephants.

Great chain of being

Great chain of being

The great chain of being is a hierarchical structure of all matter and life, thought by medieval Christianity to have been decreed by God. The chain begins with God and descends through angels, humans, animals and plants to minerals.

Robert Hooke

Robert Hooke

Robert Hooke FRS was an English polymath active as a scientist, natural philosopher and architect, who is credited to be one of the first two scientists to discover microorganisms in 1665 using a compound microscope that he built himself, the other scientist being Antoni van Leeuwenhoek in 1674. An impoverished scientific inquirer in young adulthood, he found wealth and esteem by performing over half of the architectural surveys after London's great fire of 1666. Hooke was also a member of the Royal Society and since 1662 was its curator of experiments. Hooke was also Professor of Geometry at Gresham College.

Nautilus

Nautilus

The nautilus is a pelagic marine mollusc of the cephalopod family Nautilidae. The nautilus is the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina.

Royal Society

Royal Society

The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, recognising excellence in science, supporting outstanding science, providing scientific advice for policy, education and public engagement and fostering international and global co-operation. Founded on 28 November 1660, it was granted a royal charter by King Charles II as The Royal Society and is the oldest continuously existing scientific academy in the world.

Ireland

Ireland

Ireland is an island in the North Atlantic Ocean, in north-western Europe. It is separated from Great Britain to its east by the North Channel, the Irish Sea, and St George's Channel. Ireland is the second-largest island of the British Isles, the third-largest in Europe, and the twentieth-largest in the world.

Moose

Moose

The moose or elk is a member of the New World deer subfamily and is the only species in the genus Alces. It is the largest and heaviest extant species in the deer family. Most adult male moose have distinctive broad, palmate antlers; most other members of the deer family have antlers with a dendritic ("twig-like") configuration. Moose typically inhabit boreal forests and temperate broadleaf and mixed forests of the Northern Hemisphere in temperate to subarctic climates. Hunting and other human activities have caused a reduction in the size of the moose's range over time. It has been reintroduced to some of its former habitats. Currently, most moose occur in Canada, Alaska, New England, New York State, Fennoscandia, the Baltic states, Poland, Kazakhstan, and Russia.

British Isles

British Isles

The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isles, and over six thousand smaller islands. They have a total area of 315,159 km2 (121,684 sq mi) and a combined population of almost 72 million, and include two sovereign states, the Republic of Ireland, and the United Kingdom of Great Britain and Northern Ireland. The Channel Islands, off the north coast of France, are normally taken to be part of the British Isles, even though they do not form part of the archipelago.

Deer

Deer

Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including muntjac, elk (wapiti), red deer, and fallow deer; and the Capreolinae, including reindeer (caribou), white-tailed deer, roe deer, and moose. Male deer of all species, as well as female reindeer, grow and shed new antlers each year. In this, they differ from permanently horned antelope, which are part of a different family (Bovidae) within the same order of even-toed ungulates (Artiodactyla).

Megaloceros

Megaloceros

Megaloceros is an extinct genus of deer whose members lived throughout Eurasia from the early Pleistocene to the beginning of the Holocene and were important herbivores during the Ice Ages. The type and only certain member of the genus, Megaloceros giganteus, vernacularly known as the "Irish elk" or "giant elk", is also the best known. Fallow deer are thought to be their closest living relatives.

Human attitudes and interests

A great hammerhead caught by a sport fisherman. Human exploitation now threatens the survival of this species. Overfishing is the primary driver of shark population declines, which have fallen over 71% since 1970.[92][93]
A great hammerhead caught by a sport fisherman. Human exploitation now threatens the survival of this species. Overfishing is the primary driver of shark population declines, which have fallen over 71% since 1970.[92][93]

Extinction is an important research topic in the field of zoology, and biology in general, and has also become an area of concern outside the scientific community. A number of organizations, such as the Worldwide Fund for Nature, have been created with the goal of preserving species from extinction. Governments have attempted, through enacting laws, to avoid habitat destruction, agricultural over-harvesting, and pollution. While many human-caused extinctions have been accidental, humans have also engaged in the deliberate destruction of some species, such as dangerous viruses, and the total destruction of other problematic species has been suggested. Other species were deliberately driven to extinction, or nearly so, due to poaching or because they were "undesirable", or to push for other human agendas. One example was the near extinction of the American bison, which was nearly wiped out by mass hunts sanctioned by the United States government, to force the removal of Native Americans, many of whom relied on the bison for food.[94]

Biologist Bruce Walsh states three reasons for scientific interest in the preservation of species: genetic resources, ecosystem stability, and ethics; and today the scientific community "stress[es] the importance" of maintaining biodiversity.[95][96]

In modern times, commercial and industrial interests often have to contend with the effects of production on plant and animal life. However, some technologies with minimal, or no, proven harmful effects on Homo sapiens can be devastating to wildlife (for example, DDT).[97][98] Biogeographer Jared Diamond notes that while big business may label environmental concerns as "exaggerated", and often cause "devastating damage", some corporations find it in their interest to adopt good conservation practices, and even engage in preservation efforts that surpass those taken by national parks.[99]

Governments sometimes see the loss of native species as a loss to ecotourism,[100] and can enact laws with severe punishment against the trade in native species in an effort to prevent extinction in the wild. Nature preserves are created by governments as a means to provide continuing habitats to species crowded by human expansion. The 1992 Convention on Biological Diversity has resulted in international Biodiversity Action Plan programmes, which attempt to provide comprehensive guidelines for government biodiversity conservation. Advocacy groups, such as The Wildlands Project[101] and the Alliance for Zero Extinctions,[102] work to educate the public and pressure governments into action.

People who live close to nature can be dependent on the survival of all the species in their environment, leaving them highly exposed to extinction risks. However, people prioritize day-to-day survival over species conservation; with human overpopulation in tropical developing countries, there has been enormous pressure on forests due to subsistence agriculture, including slash-and-burn agricultural techniques that can reduce endangered species's habitats.[103]

Antinatalist philosopher David Benatar concludes that any popular concern about non-human species extinction usually arises out of concern about how the loss of a species will impact human wants and needs, that "we shall live in a world impoverished by the loss of one aspect of faunal diversity, that we shall no longer be able to behold or use that species of animal." He notes that typical concerns about possible human extinction, such as the loss of individual members, are not considered in regards to non-human species extinction.[104] Anthropologist Jason Hickel speculates that the reason humanity seems largely indifferent to anthropogenic mass species extinction is that we see ourselves as separate from the natural world and the organisms within it. He says that this is due in part to the logic of capitalism: "that the world is not really alive, and it is certainly not our kin, but rather just stuff to be extracted and discarded – and that includes most of the human beings living here too."[105]

Planned extinction

Completed

Proposed

The poliovirus is now confined to small parts of the world due to extermination efforts.[108]

Dracunculus medinensis, or Guinea worm, a parasitic worm which causes the disease dracunculiasis, is now close to eradication thanks to efforts led by the Carter Center.[109]

Treponema pallidum pertenue, a bacterium which causes the disease yaws, is in the process of being eradicated.

Biologist Olivia Judson has advocated the deliberate extinction of certain disease-carrying mosquito species. In a September 25, 2003 article in The New York Times, she advocated "specicide" of thirty mosquito species by introducing a genetic element that can insert itself into another crucial gene, to create recessive "knockout genes".[110] She says that the Anopheles mosquitoes (which spread malaria) and Aedes mosquitoes (which spread dengue fever, yellow fever, elephantiasis, and other diseases) represent only 30 of around 3,500 mosquito species; eradicating these would save at least one million human lives per year, at a cost of reducing the genetic diversity of the family Culicidae by only 1%. She further argues that since species become extinct "all the time" the disappearance of a few more will not destroy the ecosystem: "We're not left with a wasteland every time a species vanishes. Removing one species sometimes causes shifts in the populations of other species—but different need not mean worse." In addition, anti-malarial and mosquito control programs offer little realistic hope to the 300 million people in developing nations who will be infected with acute illnesses this year. Although trials are ongoing, she writes that if they fail "we should consider the ultimate swatting."[110]

Biologist E. O. Wilson has advocated the eradication of several species of mosquito, including malaria vector Anopheles gambiae. Wilson stated, "I'm talking about a very small number of species that have co-evolved with us and are preying on humans, so it would certainly be acceptable to remove them. I believe it's just common sense."[111]

There have been many campaigns – some successful – to locally eradicate tsetse flies and their trypanosomes in areas, countries, and islands of Africa (including Príncipe).[112][113] There are currently serious efforts to do away with them all across Africa, and this is generally viewed as beneficial and morally necessary,[114] although not always.[115]

Cloning

Some, such as Harvard geneticist George M. Church, believe that ongoing technological advances will let us "bring back to life" an extinct species by cloning, using DNA from the remains of that species. Proposed targets for cloning include the mammoth, the thylacine, and the Pyrenean ibex. For this to succeed, enough individuals would have to be cloned, from the DNA of different individuals (in the case of sexually reproducing organisms) to create a viable population. Though bioethical and philosophical objections have been raised,[116] the cloning of extinct creatures seems theoretically possible.[117]

In 2003, scientists tried to clone the extinct Pyrenean ibex (C. p. pyrenaica). This attempt failed: of the 285 embryos reconstructed, 54 were transferred to 12 mountain goats and mountain goat–domestic goat hybrids, but only two survived the initial two months of gestation before they, too, died.[118] In 2009, a second attempt was made to clone the Pyrenean ibex: one clone was born alive, but died seven minutes later, due to physical defects in the lungs.[119]

Discover more about Human attitudes and interests related topics

Great hammerhead

Great hammerhead

The great hammerhead or great hammerhead shark is the largest species of hammerhead shark, belonging to the family Sphyrnidae, attaining an average length of 4.6 m (15 ft) and reaching a maximum length of 6.1 m (20 ft). It is found in tropical and warm temperate waters worldwide, inhabiting coastal areas and the continental shelf. The great hammerhead can be distinguished from other hammerheads by the shape of its "hammer", which is wide with an almost straight front margin, and by its tall, sickle-shaped first dorsal fin. A solitary, strong-swimming apex predator, the great hammerhead feeds on a wide variety of prey ranging from crustaceans and cephalopods, to bony fish, to smaller sharks. Observations of this species in the wild suggest that the cephalofoil functions to immobilize stingrays, a favored prey. This species has a viviparous mode of reproduction, bearing litters of up to 50 pups every two years.

Biology

Biology

Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary information encoded in genes, which can be transmitted to future generations. Another major theme is evolution, which explains the unity and diversity of life. Energy processing is also important to life as it allows organisms to move, grow, and reproduce. Finally, all organisms are able to regulate their own internal environments.

Government

Government

A government is the system or group of people governing an organized community, generally a state.

American bison

American bison

The American bison is a species of bison native to North America. Sometimes colloquially referred to as American buffalo or simply buffalo, it is one of two extant species of bison, alongside the European bison. Its historical range, by 9000 BC, is described as the great bison belt, a tract of rich grassland that ran from Alaska to the Gulf of Mexico, east to the Atlantic Seaboard as far north as New York, south to Georgia and, according to some sources, further south to Florida, with sightings in North Carolina near Buffalo Ford on the Catawba River as late as 1750. Once roaming in vast herds, the species nearly became extinct by a combination of commercial hunting and slaughter in the 19th century and introduction of bovine diseases from domestic cattle. With a population of 60 million in the late 18th century, the species was culled down to just 541 animals by 1889. Recovery efforts expanded in the mid-20th century, with a resurgence to roughly 31,000 wild bison as of March 2019. For many years, the population was primarily found in a few national parks and reserves. Through multiple reintroductions, the species now freely roams wild in several regions in the United States, Canada, and Mexico, with it also being introduced to Yakutia in Russia.

Indigenous peoples of the Americas

Indigenous peoples of the Americas

The Indigenous peoples of the Americas are the inhabitants of the Americas before the arrival of the European settlers in the 15th century, and the ethnic groups who now identify themselves with those peoples.

Ethics

Ethics

Ethics or moral philosophy is a branch of philosophy that "involves systematizing, defending, and recommending concepts of right and wrong behavior". The field of ethics, along with aesthetics, concerns matters of value; these fields comprise the branch of philosophy called axiology.

DDT

DDT

Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. DDT was first synthesized in 1874 by the Austrian chemist Othmar Zeidler. DDT's insecticidal action was discovered by the Swiss chemist Paul Hermann Müller in 1939. DDT was used in the second half of World War II to limit the spread of the insect-borne diseases malaria and typhus among civilians and troops. Müller was awarded the Nobel Prize in Physiology or Medicine in 1948 "for his discovery of the high efficiency of DDT as a contact poison against several arthropods".

Biogeography

Biogeography

Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, isolation and habitat area. Phytogeography is the branch of biogeography that studies the distribution of plants. Zoogeography is the branch that studies distribution of animals. Mycogeography is the branch that studies distribution of fungi, such as mushrooms.

Jared Diamond

Jared Diamond

Jared Mason Diamond is an American geographer, historian, ornithologist, and author best known for his popular science books The Third Chimpanzee (1991); Guns, Germs, and Steel ; Collapse (2005), The World Until Yesterday (2012), and Upheaval (2019). Originally trained in biochemistry and physiology, Diamond is known for drawing from a variety of fields, including anthropology, ecology, geography, and evolutionary biology. He is a professor of geography at UCLA.

Big business

Big business

Big business involves large-scale corporate-controlled financial or business activities. As a term, it describes activities that run from "huge transactions" to the more general "doing big things". In corporate jargon, the concept is commonly known as enterprise, or activities involving enterprise customers.

Ecotourism

Ecotourism

Ecotourism is a form of tourism involving responsible travel to natural areas, conserving the environment, and improving the well-being of the local people. Its purpose may be to educate the traveler, to provide funds for ecological conservation, to directly benefit the economic development and political empowerment of local communities, or to foster respect for different cultures and for human rights. Since the 1980s, ecotourism has been considered a critical endeavor by environmentalists, so that future generations may experience destinations relatively untouched by human intervention. Ecotourism may focus on educating travelers on local environments and natural surroundings with an eye to ecological conservation. Some include in the definition of ecotourism the effort to produce economic opportunities that make conservation of natural resources financially possible.

Convention on Biological Diversity

Convention on Biological Diversity

The Convention on Biological Diversity (CBD), known informally as the Biodiversity Convention, is a multilateral treaty. The Convention has three main goals: the conservation of biological diversity ; the sustainable use of its components; and the fair and equitable sharing of benefits arising from genetic resources. Its objective is to develop national strategies for the conservation and sustainable use of biological diversity, and it is often seen as the key document regarding sustainable development.

Source: "Extinction", Wikipedia, Wikimedia Foundation, (2023, March 22nd), https://en.wikipedia.org/wiki/Extinction.

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References
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