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= Extinction =
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Introduction
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Extinction is the termination of an organism by the death of its last
member. A taxon may become functionally extinct before the death of
its last member if it loses the capacity to reproduce and recover. As
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.
Over five billion species are estimated to have died out. It is
estimated that there are currently around 8.7 million species of
eukaryotes globally, possibly many times more if microorganisms are
included. Notable extinct animal species include non-avian dinosaurs,
saber-toothed cats, and mammoths. Through evolution, species arise
through the process of speciation. 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. A typical species
becomes extinct within 10 million years of its first appearance,
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. Only recently have extinctions been
recorded with scientists alarmed at the current high rate of
extinctions. 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. 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.
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. In a subsequent report, IPBES listed
unsustainable fishing, hunting and logging as being some of the
primary drivers of the global extinction crisis. In June 2019, one
million species of plants and animals were at risk of extinction. At
least 571 plant species have been lost since 1750. 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.
A dagger symbol (†) placed next to the name of a species or other
taxon normally indicates its status as extinct.
Definition
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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.
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.
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. 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". 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
mammal diversity to what it was before the human era.
Pseudoextinction
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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, or split into more than one (cladogenesis).
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
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A Lazarus taxon or Lazarus species refers to instances where a species
or taxon was thought to be extinct, but was later rediscovered. It can
also refer to instances where large gaps in the fossil record of a
taxon result in fossils reappearing much later, although the taxon may
have ultimately become extinct at a later point.
The coelacanth, a fish related to lungfish and tetrapods, is an
example of a Lazarus taxon that was known only from the fossil record
and 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.
'Calliostoma bullatum', a species of deepwater sea snail originally
described from fossils in 1844 proved to be a Lazarus species when
extant individuals were described in 2019.
Attenborough's long-beaked echidna ('Zaglossus attenboroughi') is an
example of a Lazarus species from Papua New Guinea that had last been
sighted in 1962 and believed to be possibly extinct, until it was
recorded again in November 2023.
Some species thought to be extinct have had ongoing speculation that
they may still exist, and in the event of rediscovery would be
considered Lazarus species. Examples 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.
Causes
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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, 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". 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. 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. 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. 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. 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. 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.
Genetics and demographic phenomena
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If adaptation increasing population fitness is slower than
environmental degradation plus the accumulation of slightly
deleterious mutations, then a population will go extinct. 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. 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
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Extinction sometimes results for species evolved to specific ecologies
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. 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; 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.
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.
Replacing native with alien genes narrows genetic diversity within
the original population,
thereby increasing the chance of extinction.
Habitat degradation
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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 destruction, particularly the removal of vegetation that
stabilizes soil, enhances erosion and diminishes nutrient availability
in terrestrial ecosystems. This degradation can lead to a reduction in
agricultural productivity. Furthermore, increased erosion contributes
to poorer water quality by elevating the levels of sediment and
pollutants in rivers and streams.
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; 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.
Diminished resources or introduction of new competitor species also
often accompany habitat degradation. Global warming has allowed some
species to expand their range, bringing 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.
Predation, competition, and disease
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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, interspecific 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 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.
Coextinction
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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." 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.
Climate change
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Extinction as a result of climate change has been confirmed by fossil
studies. Particularly, the extinction of amphibians during the
Carboniferous Rainforest Collapse, 305 million years ago. 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. 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. Climate change has
also been found to be a factor in habitat loss and desertification.
Sexual selection and male investment
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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.
Mass extinctions
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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,
which is estimated to have killed 90% of species then existing. There
is also evidence to suggest that this event was preceded by another
mass extinction, known as Olson's Extinction. 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
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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,
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. 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." A 2025 study found that
human activities are to blame for biodiversity loss across all species
and ecosystems.
Biologist E. O. Wilson estimated 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. 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),
faster than at any other time in human history, while future rates are
likely 10,000 times higher. 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.
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. 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. 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". 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."
History of scientific understanding
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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.
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. 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. Thomas Jefferson was a firm supporter of
the great chain of being and an opponent of extinction, famously
denying the extinction of the woolly mammoth on the grounds that
nature never allows a race of animals to become extinct.
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, 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.
While he contended that it was possible a species could be "lost", he
thought this highly unlikely. 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. Molyneux reasoned that they
came from the North American moose and that the animal had once been
common on the British Isles. 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.
The antlers were later confirmed to be from the extinct deer
'Megaloceros'. 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.
Georges Cuvier is credited with establishing the modern conception of
extinction in a 1796 lecture to the French Institute, though he would
spend most of his career trying to convince the wider scientific
community of his theory. Cuvier was a well-regarded geologist, lauded
for his ability to reconstruct the anatomy of an unknown species from
a few fragments of bone. His primary evidence for extinction came from
mammoth skulls found near Paris. 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. In
1798, he studied a fossil from the Paris Basin that was first observed
by Robert de Lamanon in 1782, first hypothesizing that it belonged to
a canine but then deciding that it instead belonged to an animal that
was unlike living ones. His study paved the way to his naming of the
extinct mammal genus 'Palaeotherium' in 1804 based on the skull and
additional fossil material along with another extinct contemporary
mammal genus 'Anoplotherium'. In both genera, he noticed that their
fossils shared some similarities with other mammals like ruminants and
rhinoceroses but still had distinct differences. In 1812, Cuvier,
along with Alexandre Brongniart and Geoffroy Saint-Hilaire, mapped the
strata of the Paris basin. They saw alternating saltwater and
freshwater deposits, as well as patterns of the appearance and
disappearance of fossils throughout the record. From these patterns,
Cuvier inferred historic cycles of catastrophic flooding, extinction,
and repopulation of the earth with new species.
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. The primary debate focused on whether this turnover
caused by extinction was gradual or abrupt in nature. 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. His catastrophic view of the nature of extinction
garnered him many opponents in the newly emerging school of
uniformitarianism.
Jean-Baptiste Lamarck, a gradualist and colleague of Cuvier, saw the
fossils of different life forms as evidence of the mutable character
of species. 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. 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.
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. He similarly argued against
mass extinctions, believing that any extinction must be a gradual
process. 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.
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. 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). 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.
Human attitudes and interests
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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.
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.
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).
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.
Governments sometimes see the loss of native species as a loss to
ecotourism, 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 and the Alliance for
Zero Extinctions, 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.
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.
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."
Completed
===========
* The smallpox virus is now extinct in the wild, although samples are
retained in laboratory settings.
* The rinderpest virus, which infected domestic cattle, is now extinct
in the wild.
Disease agents
================
The poliovirus is now confined to small parts of the world due to
extermination efforts.
'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.
'Treponema pallidum pertenue', a bacterium which causes the disease
yaws, is in the process of being eradicated.
Disease vectors
=================
Biologist Olivia Judson has advocated the deliberate extinction of
certain disease-carrying mosquito species. In an article in 'The New
York Times' on 25 September 2003, 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". 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".
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."
There have been many campaigns - some successful - to locally
eradicate tsetse flies and their trypanosomes in areas, countries, and
islands of Africa (including Príncipe). There are currently serious
efforts to do away with them all across Africa, and this is generally
viewed as beneficial and morally necessary, although not always.
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, the cloning of extinct creatures seems theoretically
possible.
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 Spanish ibexes and ibex-domestic goat hybrids,
but only two survived the initial two months of gestation before they,
too, died. 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.
External links
======================================================================
* [
http://creo.amnh.org Committee on recently extinct organisms]
*
[
https://www.theguardian.com/environment/series/the-age-of-extinction
The age of extinction] series in 'The Guardian'
* [
http://sresearch.scienceontheweb.net/evolution.php Extincion events
connected with New theory of evolution]
License
=========
All content on Gopherpedia comes from Wikipedia, and is licensed under CC-BY-SA
License URL:
http://creativecommons.org/licenses/by-sa/3.0/
Original Article:
http://en.wikipedia.org/wiki/Extinction
