Extinction

Extinction

Overview

In biology
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

 and ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

, extinction is the end of an organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

 or of a group of organisms (taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

), normally a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

. 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
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...

 may have been lost before this point. Because a species' potential range
Range (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...

 may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa
Lazarus taxon
In paleontology, a Lazarus taxon is a taxon that disappears from one or more periods of the fossil record, only to appear again later. The term refers to the account in the Gospel of John, in which Jesus raised Lazarus from the dead...

, where a species presumed extinct abruptly "re-appears" (typically in the fossil record
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

) after a period of apparent absence.

Through evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

, new species arise through the process of speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...

—where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...

—and species become extinct when they are no longer able to survive in changing conditions or against superior competition.
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Quotations

The Dodo never had a chance. He seems to have been invented for the sole purpose of becoming extinct and that was all he was good for. -- id.

Becoming extinct has its compensations. It's a good deal like beating the game. I would go so far as to say that becoming extinct is the perfect answer to everything and I defy anybody to think of a better. Other solutions are mere palliatives, just a bunch of loose ends, leaving the central problem untouched. --id.

"EXTINCTION: The end of the line for creatures that cannot or will not adapt to an increasingly hostile environment, which is why the future belongs to cockroaches and MBAs." -- Rick Bayan, The Cynic's Dictionary

Since after extinction no one will be present to take responsibility, we have to take full responsibility now. -- Jonathan Schell|Jonathan Schell, The Fate of the Earth, 1982, ISBN 0-39452-559-0

The beauty and genius of a work of art may be reconceived, though its first material expression be destroyed; a vanished harmony may yet again inspire the composer; but when the last individual of a race of living beings breathes no more, another heaven and another earth must pass before such a one can be again. -- William Beebe, The Bird, 1906

Extinction is forever. -- popular slogan. Category:Themes

Encyclopedia

In biology
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

 and ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

, extinction is the end of an organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

 or of a group of organisms (taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

), normally a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

. 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
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...

 may have been lost before this point. Because a species' potential range
Range (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...

 may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa
Lazarus taxon
In paleontology, a Lazarus taxon is a taxon that disappears from one or more periods of the fossil record, only to appear again later. The term refers to the account in the Gospel of John, in which Jesus raised Lazarus from the dead...

, where a species presumed extinct abruptly "re-appears" (typically in the fossil record
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

) after a period of apparent absence.

Through evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

, new species arise through the process of speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...

—where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...

—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. A typical species becomes extinct within 10 million years of its first appearance, although some species, called living fossil
Living fossil
Living fossil is an informal term for any living species which appears similar to a species otherwise only known from fossils and which has no close living relatives, or a group of organisms which have long fossil records...

s, survive virtually unchanged for hundreds of millions of years. Most extinctions have occurred naturally, prior to Homo sapiens walking on Earth: it is estimated that 99.9% of all species that have ever existed are now extinct.

Mass extinction
Extinction event
An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...

s are relatively rare events; however, isolated extinctions are quite common. Only recently have extinctions been recorded and scientists have become alarmed at the high rates of recent extinctions. Most species that become extinct are never scientifically documented. Some scientists estimate that up to half of presently existing species may become extinct by 2100. It is difficult to estimate the trajectory that biodiversity might have taken without human impact but scientists at the University of Bristol estimate that biodiversity might increase exponentially without human influence.

Definition


A species becomes extinct when the last existing member of that species dies. Extinction therefore becomes a certainty when there are no surviving individuals that are able to reproduce and create a new generation. A species may become functionally extinct
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...

 when only a handful of individuals survive, which are unable to reproduce due to poor health, age, sparse distribution over a large range, a lack of individuals of both sexes (in sexually reproducing
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...

 species), or other reasons.

Pinpointing the extinction (or pseudoextinction
Pseudoextinction
Pseudoextinction of a species occurs where there are no more living members of that species, but members of a daughter species or subspecies remain alive. As all species must have an ancestor of a previous species, much of evolution is believed to occur through 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 identifiable from any ancestor or daughter species, or from other closely related species. Extinction of a species (or replacement by a daughter species) plays a key role in the punctuated equilibrium
Punctuated equilibrium
Punctuated equilibrium is a theory in evolutionary biology which proposes that most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state called stasis...

 hypothesis of Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....

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

.

In ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

, extinction is often used informally to refer to local extinction
Local extinction
Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...

, in which a species ceases to exist in the chosen area of study, but still exists elsewhere. This phenomenon is also known as extirpation. Local extinctions may be followed by a replacement of the species taken from other locations; wolf reintroduction
Wolf reintroduction
Wolf reintroduction involves the artificial reestablishment of a population of wolves in areas where they have been extirpated. Wolf reintroduction is only considered where large tracts of suitable wilderness still exist and where certain prey species are abundant enough to support a predetermined...

 is an example of this. Species which are not extinct are termed extant. Those that are extant but threatened by extinction are referred to as threatened or endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...

.

An important aspect of extinction at the present time are human attempts to preserve critically endangered species, which is reflected by the creation of the conservation status
Conservation status
The conservation status of a group of organisms indicates whether the group is still extant and how likely the group is to become extinct in the near future...

 "Extinct in the Wild" (EW)
Extinct in the Wild
Extinct in the Wild is a conservation status assigned to species or lower taxa, the only known living members of which are being kept in captivity or as a naturalized population outside its historic range.-Examples:...

. 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 zoo
Zoo
A zoological garden, zoological park, menagerie, or zoo is a facility in which animals are confined within enclosures, displayed to the public, and in which they may also be bred....

s 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
Zoology
Zoology |zoölogy]]), is the branch of biology that relates to the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct...

 institutions attempt to maintain a viable population for species preservation and possible future reintroduction
Reintroduction
Reintroduction is the deliberate release of a species into the wild in zones formerly inhabited by said species but where it has disappeared from for a number of reasons, from captivity or relocated from other areas where the species still survives in...

 to the wild through use of carefully planned breeding program
Breeding program
Breeding programs help animals to breed and can be good for animals as well as the agricultural economy.A breeding program is the planned breeding of a group of animals or plants, usually involving at least several individuals and extending over several generations...

s.

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
Keystone species
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and...

.

Pseudoextinction


Descendants may or may not exist for extinct species. Daughter species that evolve from a parent species carry on most of the parent species' genetic information
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...

, and even though the parent species may become extinct, the daughter species lives on. In other cases, species have produced no new variants, or none that are able to survive the parent species' extinction. Extinction of a parent species where daughter species or subspecies are still alive is also called pseudoextinction
Pseudoextinction
Pseudoextinction of a species occurs where there are no more living members of that species, but members of a daughter species or subspecies remain alive. As all species must have an ancestor of a previous species, much of evolution is believed to occur through pseudoextinction...

.

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
Hyracotherium
Hyracotherium , also known as Eohippus or the dawn horse, is an extinct genus of very small perissodactyl ungulates that lived in the woodlands of the northern hemisphere, with species ranging throughout Asia, Europe, and North America during the early Tertiary Period and the early to mid Eocene...

, which was an early horse that shares a common ancestor with the modern horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...

, is pseudoextinct, rather than extinct, because there are several extant species of Equus
Equus (genus)
Equus is a genus of animals in the family Equidae that includes horses, donkeys, and zebras. Within Equidae, Equus is the only extant genus. Like Equidae more broadly, Equus has numerous extinct species known only from fossils. This article deals primarily with the extant species.The term equine...

, including zebra
Zebra
Zebras are several species of African equids united by their distinctive black and white stripes. Their stripes come in different patterns unique to each individual. They are generally social animals that live in small harems to large herds...

 and donkeys. However, as fossil species typically leave no genetic material behind, it is not possible to say whether Hyracotherium actually evolved into more modern horse species
Evolution of the horse
The evolution of the horse pertains to the phylogenetic ancestry of the modern horse from the small dog-sized, forest-dwelling Hyracotherium over geologic time scales...

 or simply evolved from a common ancestor with modern horses. Pseudoextinction is much easier to demonstrate for larger taxonomic groups.

Causes



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 life-span of most species is 10 million years, although this varies widely between taxa.
There are a variety of causes that 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
Stephen C. Stearns
Stephen C. Stearns is an American biologist, the Edward P. Bass Professor of Ecology and Evolutionary Biology at Yale University...

, "so is each extinction ... the causes for each are varied—some subtle and complex, others obvious and simple". Most simply, any species that is unable to survive
Survival skills
Survival skills are techniques a person may use in a dangerous situation to save themselves or others...

 or reproduce in its environment, and unable to 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
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

 renders its entire habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

 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 take place a long time after the events that set it in motion, a phenomenon known as extinction debt
Extinction debt
Extinction debt is a concept in ecology that describes the future extinction of species due to events in the past. Extinction debt occurs because of time delays between impacts on a species, such as destruction of habitat, and the species' ultimate disappearance...

.

Assessing the relative importance of genetic factors compared to environmental ones as the causes of extinction has been compared to the nature-nurture debate. The question of whether more extinctions in the fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 record have been caused by evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

 or by catastrophe is a subject of discussion; Mark Newman, the author of Modeling Extinction argues for a mathematical model that falls between the two positions. By contrast, conservation biology
Conservation biology
Conservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction...

 uses the 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. Developed by M. E. Gilpin and M. E...

 model to classify extinctions by cause. When concerns about human extinction
Human extinction
Human extinction is the end of the human species. Various scenarios have been discussed in science, popular culture, and religion . The scope of this article is existential risks. Humans are very widespread on the Earth, and live in communities which are capable of some kind of basic survival in...

 have been raised, for example in Sir Martin Rees' 2003 book 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...

, those concerns lie with the effects of climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

 or technological
Technology
Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...

 disaster.

Currently, environmental groups and some governments are concerned with the extinction of species caused by humanity, and are attempting to combat further extinctions through a variety of conservation
Conservation movement
The conservation movement, also known as nature conservation, is a political, environmental and a social movement that seeks to protect natural resources including animal, fungus and plant species as well as their habitat for the future....

 programs. Humans can cause extinction of a species through overharvesting, pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

, habitat destruction
Habitat destruction
Habitat destruction is the process in which natural habitat is rendered functionally unable to support the species present. In this process, the organisms that previously used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity mainly for the purpose of...

, introduction of new predators and food competitors, overhunting, and other influences. Explosive, unsustainable human population growth
Population growth
Population growth is the change in a population over time, and can be quantified as the change in the number of individuals of any species in a population using "per unit time" for measurement....

 is an essential cause of the extinction crisis. According to the International Union for Conservation of Nature (IUCN), 784 extinctions have been recorded since the year 1500 (to the year 2004), the arbitrary date selected to define "modern" extinctions, with many more likely to have gone unnoticed (several species have also been listed as extinct since the 2004 date).

Genetics and demographic phenomena



Population genetics
Population genetics
Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...

 and demographic phenomena affect the evolution, and therefore the risk of extinction, of species. Limited geographic range is the most important determinant of genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 extinction at background rates but becomes increasingly irrelevant as mass extinction arises.

Natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

 acts to propagate beneficial genetic traits and eliminate weaknesses. It is nevertheless possible for a deleterious mutation to be spread throughout a population through the effect of genetic drift
Genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...

.

Because traits are selected and not genes, the relationship between genetic diversity and extinction risk can be complex with factors such as balancing selection
Balancing selection
Balancing selection refers to a number of selective processes by which multiple alleles are actively maintained in the gene pool of a population at frequencies above that of gene mutation. This usually happens when the heterozygotes for the alleles under consideration have a higher adaptive value...

, cryptic genetic variation, phenotypic plasticity
Phenotypic plasticity
Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...

, and degeneracy
Degeneracy (biology)
Within biological systems, degeneracy refers to circumstances where structurally dissimilar components/modules/pathways can perform similar functions under certain conditions, but perform distinct functions in other conditions. Degeneracy is thus a relational property that requires comparing the...

 all playing potential roles.

A diverse or deep gene pool
Gene pool
In population genetics, a gene pool is the complete set of unique alleles in a species or population.- Description :A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection...

 gives a population a higher chance of surviving an adverse change in conditions. Effects that cause or reward a loss in genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....

 can increase the chances of extinction of a species. Population bottleneck
Population bottleneck
A population bottleneck is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing....

s can dramatically reduce genetic diversity by severely limiting the number of reproducing individuals and make inbreeding
Inbreeding
Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...

 more frequent. The founder effect
Founder effect
In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It was first fully outlined by Ernst Mayr in 1942, using existing theoretical work by those such as Sewall...

 can cause rapid, individual-based speciation and is the most dramatic example of a population bottleneck.

Genetic pollution



Purebred
Purebred
Purebreds, also called purebreeds, are cultivated varieties or cultivars of an animal species, achieved through the process of selective breeding...

 wild species evolved to a specific ecology can be threatened with extinction through the process of genetic pollution
Genetic pollution
Genetic pollution is a controversial term for uncontrolled gene flow into wild populations. This gene flow is undesirable according to some environmentalists and conservationists, including groups such as Greenpeace, TRAFFIC, and GeneWatch UK.-Usage:...

—i.e., uncontrolled hybridization, introgression
Introgression
Introgression, also known as introgressive hybridization, in genetics is the movement of a gene from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species...

 genetic swamping which leads to homogenization or out-competition
Fitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...

 from the introduced (or hybrid
Heterosis
Heterosis, or hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. The adjective derived from heterosis is heterotic....

) species. Endemic populations can face such extinctions when new populations are imported or selectively bred
Selective breeding
Selective breeding is the process of breeding plants and animals for particular genetic traits. Typically, strains that are selectively bred are domesticated, and the breeding is sometimes done by a professional breeder. Bred animals are known as breeds, while bred plants are known as varieties,...

 by people, or when habitat modification brings previously isolated species into contact. Extinction is likeliest for rare species
Rare species
A rare species is a group of organisms that are very uncommon or scarce. This designation may be applied to either a plant or animal taxon, and may be distinct from the term "endangered" or "threatened species" but not "extinct"....

 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
Water Buffalo
The water buffalo or domestic Asian water buffalo is a large bovine animal, frequently used as livestock in southern Asia, and also widely in South America, southern Europe, northern Africa, and elsewhere....

). Such extinctions are not always apparent from morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 (non-genetic) observations. Some degree of gene flow
Gene flow
In population genetics, gene flow is the transfer of alleles of genes from one population to another.Migration into or out of a population may be responsible for a marked change in allele frequencies...

 is a normal evolutionarily process, nevertheless, hybridization (with or without introgression) threatens rare species' existence.

The gene pool
Gene pool
In population genetics, a gene pool is the complete set of unique alleles in a species or population.- Description :A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection...

 of a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 or a population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...

 is the variety of genetic information in its living members. A large gene pool (extensive genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....

) is associated with robust populations that can survive bouts of intense selection
Selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...

. Meanwhile, low genetic diversity (see inbreeding
Inbreeding
Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...

 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



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
Habitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...

 may alter the fitness landscape
Fitness landscape
In evolutionary biology, fitness landscapes or adaptive landscapes are used to visualize the relationship between genotypes and reproductive success. It is assumed that every genotype has a well-defined replication rate . This fitness is the "height" of the 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
Toxicity
Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...

, 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
Contamination
Contamination is the presence of a minor and unwanted constituent in material, physical body, natural environment, at a workplace, etc.-Specifics:"Contamination" also has more specific meanings in science:...

 or sterilizing
Sterilization (microbiology)
Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...

 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 rainforest
Tropical rainforest
A tropical rainforest is an ecosystem type that occurs roughly within the latitudes 28 degrees north or south of the equator . This ecosystem experiences high average temperatures and a significant amount of rainfall...

s 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
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...

 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
Bottom trawling
Bottom trawling is trawling along the sea floor. It is also often referred to as "dragging".The scientific community divides bottom trawling into benthic trawling and demersal trawling...

.

Diminished resources or introduction of new competitor species also often accompany habitat degradation. Global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

 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
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 and food can also be limited during habitat degradation, leading to extinction.

Predation, competition, and disease


Before the evolution of hominids, life forms competed with each other and drove one another extinct. Recently in geologic time, Humans have been transporting animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s and plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s from one part of the world to another for thousands of years, sometimes deliberately (e.g., livestock
Livestock
Livestock refers to one or more domesticated animals raised in an agricultural setting to produce commodities such as food, fiber and labor. The term "livestock" as used in this article does not include poultry or farmed fish; however the inclusion of these, especially poultry, within the meaning...

 released by sailors onto islands as a source of food) and sometimes accidentally (e.g., rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...

s escaping from boats). In most cases, such introductions are unsuccessful, but when they do become established as an invasive alien species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....

, the consequences can be catastrophic. Invasive alien species can affect native
Endemic (ecology)
Endemism is the ecological state of being unique to a defined geographic location, such as an island, nation or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, all species of lemur are endemic to the...

 species directly by eating them, competing with them, and introducing pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

s 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
Megafauna
In terrestrial zoology, megafauna are "giant", "very large" or "large" animals. The most common thresholds used are or...

 in areas such as Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 (40,000 years before present), North
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

 (12,000 years before present), Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...

, Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

 (300-1000 CE), and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

 (1300-1500 CE), 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



Coextinction refers to the loss of a species due to the extinction of another; for example, the extinction of parasitic
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...

 insects following the loss of their hosts. Coextinction can also occur when a species loses its pollinator
Pollinator
A pollinator is the biotic agent that moves pollen from the male anthers of a flower to the female stigma of a flower to accomplish fertilization or syngamy of the female gamete in the ovule of the flower by the male gamete from the pollen grain...

, or to predators in a food chain
Food chain
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...

 who lose their prey. "Species coextinction is a manifestation of the interconnectedness 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
Keystone species
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and...

 goes extinct.
Models suggest that coextinction is the most common form of biodiversity loss. Coextinction allows for cascading effects across the trophic levels. Such effects are most severe in mutualistic and parasitic relationships. An example of coextinction would be the Haast's Eagle and the Moa. The Haast's Eagle is an example of a predator that became extinct because its food source became extinct. The moa were several species of flightless birds that served as a food source to the Haast's Eagle.

Climate change


Extinction as a result of climate change has been confirmed by fossil studies. Particularly, the extinction of amphibians during the Carboniferous Rainforest Collapse
Carboniferous Rainforest Collapse
The Carboniferous Rainforest Collapse was an extinction event that occurred around 305 million years ago in the Carboniferous period). Vast coal forests covered the equatorial region of Euramerica...

, 350 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
Cape floristic region
The Cape Floristic Region is a floristic region located near the southern tip of South Africa. It is the only floristic region of the Cape Floristic Kingdom, and includes only one floristic province, known as the Cape Floristic Province.The Cape Floristic Region, the smallest of the six recognised...

, and the Caribbean Basin
Caribbean Basin
The Caribbean Basin is generally defined as the area running from Florida westward along the Gulf coast, then south along the Mexican coast through Central America and then eastward across the northern coast of South America. This region includes the islands of the archipelago of the West Indies...

. 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.

Mass extinctions



There have been at least five mass extinctions in the history of life on earth, and four in the last 3.5 billion years in which many species have disappeared in a relatively short period of geological time. The massive eruptive event is considered to be one likely cause of the "Great Dying" about 250 million years ago, which is estimated to have killed 90% of species existing at the time. There is also evidence to suggest this event was preceded by another mass extinction known as Olson's Extinction
Olson's Extinction
Olson's Extinction was a mass extinction that occurred in the Early Guadalupian of the Permian period and which predated the Permian–Triassic extinction event.- Extinction Patterns :...

. The Cretaceous–Tertiary extinction event occurred 65 million years ago at the end of the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 period and is best known for having wiped out non-avian dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s, among many other species.

Modern extinctions


According to a 1998 survey of 400 biologists conducted by New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

's American Museum of Natural History
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...

, nearly 70 percent believed that they were currently in the early stages of a human-caused extinction, known as the Holocene extinction. In that survey, the same proportion of respondents agreed with the prediction that up to 20 percent of all living populations could become extinct within 30 years (by 2028). Biologist E. O. Wilson
E. O. Wilson
Edward Osborne Wilson is an American biologist, researcher , theorist , naturalist and author. His biological specialty is myrmecology, the study of ants....

 estimated in 2002 that if current rates of human destruction of the biosphere continue, one-half of all species of life on earth will be extinct in 100 years. More significantly the rate of species extinctions at present is estimated at 100 to 1000 times "background" or average extinction rates in the evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

ary time scale of planet Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

.

History of scientific understanding


In the 1750s when extinction was first described, the idea of extinction was threatening to those who held a belief in the Great Chain of Being
Great chain of being
The great chain of being , is a Christian concept detailing a strict, religious hierarchical structure of all matter and life, believed to have been decreed by the Christian God.-Divisions:...

, a theological
Theology
Theology is the systematic and rational study of religion and its influences and of the nature of religious truths, or the learned profession acquired by completing specialized training in religious studies, usually at a university or school of divinity or seminary.-Definition:Augustine of Hippo...

 position that did not allow for "missing links".

The possibility of extinction was not widely accepted before the 1800s. The devoted naturalist Carl Linnaeus, could "hardly entertain" the idea that humans could cause the extinction of a species. 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
Georges Cuvier
Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...

 is credited with establishing extinction as a fact in a 1796 lecture to the French Institute. Cuvier's observations of fossil bones convinced him that they did not originate in extant animals. This discovery was critical for the spread of uniformitarianism
Uniformitarianism (science)
In the philosophy of naturalism, the uniformitarianism assumption is that the same natural laws and processes that operate in the universe now, have always operated in the universe in the past and apply everywhere in the universe. It has included the gradualistic concept that "the present is the...

, and led to the first book publicizing the idea of evolution though Cuvier himself strongly opposed the theories of evolution advanced by Lamarck and others.

Human attitudes and interests


Extinction is an important research topic in the field of zoology
Zoology
Zoology |zoölogy]]), is the branch of biology that relates to the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct...

, and biology
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

 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. Government
Government
Government refers to the legislators, administrators, and arbitrators in the administrative bureaucracy who control a state at a given time, and to the system of government by which they are organized...

s have attempted, through enacting laws, to avoid habitat destruction, agricultural over-harvesting, and pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

. While many human-caused extinctions have been accidental, humans have also engaged in the deliberate destruction of some species, such as dangerous virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

es, 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
Bison
Members of the genus Bison are large, even-toed ungulates within the subfamily Bovinae. Two extant and four extinct species are recognized...

, which was nearly wiped out by mass hunts sanctioned by the United States government, in order to force the removal of Native Americans
Indigenous peoples of the Americas
The indigenous peoples of the Americas are the pre-Columbian inhabitants of North and South America, their descendants and other ethnic groups who are identified with those peoples. Indigenous peoples are known in Canada as Aboriginal peoples, and in the United States as Native Americans...

, many of whom relied on the bison for food.

Biologist Bruce Walsh of the University of Arizona
University of Arizona
The University of Arizona is a land-grant and space-grant public institution of higher education and research located in Tucson, Arizona, United States. The University of Arizona was the first university in the state of Arizona, founded in 1885...

 states three reasons for scientific interest in the preservation of species; genetic resources, ecosystem stability, and ethics
Ethics
Ethics, also known as moral philosophy, is a branch of philosophy that addresses questions about morality—that is, concepts such as good and evil, right and wrong, virtue and vice, justice and crime, etc.Major branches of ethics include:...

; 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
DDT
DDT is one of the most well-known synthetic insecticides. It is a chemical with a long, unique, and controversial history....

). Biogeographer
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...

 Jared Diamond
Jared Diamond
Jared Mason Diamond is an American scientist and author whose work draws from a variety of fields. He is currently Professor of Geography and Physiology at UCLA...

 notes that while big business
Big Business
Big business is a term used to describe large corporations, in either an individual or collective sense. The term first came into use in a symbolic sense subsequent to the American Civil War, particularly after 1880, in connection with the combination movement that began in American business at...

 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 park
National park
A national park is a reserve of natural, semi-natural, or developed land that a sovereign state declares or owns. Although individual nations designate their own national parks differently A national park is a reserve of natural, semi-natural, or developed land that a sovereign state declares or...

s.

Governments sometimes see the loss of native species as a loss to ecotourism
Ecotourism
Ecotourism is a form of tourism visiting fragile, pristine, and usually protected areas, intended as a low impact and often small scale alternative to standard commercial tourism...

, 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
Convention on Biological Diversity
The Convention on Biological Diversity , known informally as the Biodiversity Convention, is an international legally binding treaty...

 has resulted in international Biodiversity Action Plan
Biodiversity Action Plan
A Biodiversity Action Plan is an internationally recognized program addressing threatened species and habitats and is designed to protect and restore biological systems. The original impetus for these plans derives from the 1992 Convention on Biological Diversity...

 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 risk
Risk
Risk is the potential that a chosen action or activity will lead to a loss . The notion implies that a choice having an influence on the outcome exists . Potential losses themselves may also be called "risks"...

s. However, people prioritize day-to-day survival over species conservation; with human overpopulation
Overpopulation
Overpopulation is a condition where an organism's numbers exceed the carrying capacity of its habitat. The term often refers to the relationship between the human population and its environment, the Earth...

 in tropical developing countries
Developing country
A developing country, also known as a less-developed country, is a nation with a low level of material well-being. Since no single definition of the term developing country is recognized internationally, the levels of development may vary widely within so-called developing countries...

, there has been enormous pressure on forests due to subsistence agriculture
Subsistence agriculture
Subsistence agriculture is self-sufficiency farming in which the farmers focus on growing enough food to feed their families. The typical subsistence farm has a range of crops and animals needed by the family to eat and clothe themselves during the year. Planting decisions are made with an eye...

, including slash-and-burn agricultural techniques that can reduce endangered species's habitats.

Michael Levin
Michael Levin
Michael Levin is a philosophy professor at City University of New York. He has published on metaphysics, epistemology, race, homosexuality, animal rights, the philosophy of archaeology, the philosophy of logic, philosophy of language, and the philosophy of science.Levin's central research interests...

 argues, "The very fact that a species is near extinction implies that its final demise will have negligible impact."

Planned extinction



Humans have aggressively worked toward the extinction of many species of viruses and bacteria in the cause of disease eradication
Eradication of infectious diseases
Eradication is the reduction of an infectious disease's prevalence in the global host population to zero. It is sometimes confused with elimination, which describes either the reduction of an infectious disease's prevalence in a regional population to zero, or the reduction of the global prevalence...

.

Implemented

  • The smallpox
    Smallpox
    Smallpox was an infectious disease unique to humans, caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, which is a derivative of the Latin varius, meaning "spotted", or varus, meaning "pimple"...

     virus is now extinct in the wild—although samples are retained in laboratory settings.
  • The polio virus is now confined to small parts of the world as a result of human efforts to prevent the disease it causes.
  • Guinea worm
    Dracunculiasis
    Dracunculiasis , also called guinea worm disease , is a parasitic infection caused by Dracunculus medinensis, a long and very thin nematode . The infection begins when a person drinks stagnant water contaminated with copepods infested by the larvae of the guinea worm...

  • Rinderpest
    Rinderpest
    Rinderpest was an infectious viral disease of cattle, domestic buffalo, and some other species of even-toed ungulates, including buffaloes, large antelopes and deer, giraffes, wildebeests and warthogs. After a global eradication campaign, the last confirmed case of rinderpest was diagnosed in 2001...


Proposed


Olivia Judson
Olivia Judson
Doctor Olivia P. Judson is an evolutionary biologist and science writer.- Career :Judson, who is the daughter of science historian Horace Freeland Judson,was a pupil of W.D. Hamilton....

 is one of six modern scientists to have advocated the deliberate extinction of specific species. Her September 25, 2003 New York Times article, "A Bug's Death", advocates "specicide
Genocide
Genocide is defined as "the deliberate and systematic destruction, in whole or in part, of an ethnic, racial, religious, or national group", though what constitutes enough of a "part" to qualify as genocide has been subject to much debate by legal scholars...

" of thirty mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...

 species through the introduction of a genetic element, capable of inserting itself into another crucial gene, to create recessive
Recessive
In genetics, the term "recessive gene" refers to an allele that causes a phenotype that is only seen in a homozygous genotype and never in a heterozygous genotype. Every person has two copies of every gene on autosomal chromosomes, one from mother and one from father...

 "knockout genes
Gene knockout
A gene knockout is a genetic technique in which one of an organism's genes is made inoperative . Also known as knockout organisms or simply knockouts, they are used in learning about a gene that has been sequenced, but which has an unknown or incompletely known function...

". Her arguments for doing so are that the Anopheles
Anopheles
Anopheles is a genus of mosquito. There are approximately 460 recognized species: while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus Plasmodium, which cause malaria in humans in endemic areas...

mosquitoes (which spread malaria
Malaria
Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...

) and Aedes
Aedes
Aedes is a genus of mosquito originally found in tropical and subtropical zones, but now found on all continents excluding Antarctica. Some species have been spread by human activity. Aedes albopictus, a most invasive species was recently spread to the New World, including the U.S., by the used...

mosquitoes (which spread dengue fever
Dengue fever
Dengue fever , also known as breakbone fever, is an infectious tropical disease caused by the dengue virus. Symptoms include fever, headache, muscle and joint pains, and a characteristic skin rash that is similar to measles...

, yellow fever
Yellow fever
Yellow fever is an acute viral hemorrhagic disease. The virus is a 40 to 50 nm enveloped RNA virus with positive sense of the Flaviviridae family....

, elephantiasis
Elephantiasis
Elephantiasis is a disease that is characterized by the thickening of the skin and underlying tissues, especially in the legs and male genitals. In some cases the disease can cause certain body parts, such as the scrotum, to swell to the size of a softball or basketball. It is caused by...

, and other diseases) represent only 30 species; eradicating these would save at least one million human lives per annum at a cost of reducing the genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....

 of the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 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
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

: "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-malaria
Malaria
Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...

l 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."

Cloning



Ongoing technological advances have encouraged the hypothesis that by using DNA from the remains of an extinct species, through the process of cloning, the species may be "brought back to life". Proposed targets for cloning include the dinosaurs, the mammoth
Mammoth
A mammoth is any species of the extinct genus Mammuthus. These proboscideans are members of Elephantidae, the family of elephants and mammoths, and close relatives of modern elephants. They were often equipped with long curved tusks and, in northern species, a covering of long hair...

, thylacine
Thylacine
The thylacine or ,also ;binomial name: Thylacinus cynocephalus, Greek for "dog-headed pouched one") was the largest known carnivorous marsupial of modern times. It is commonly known as the Tasmanian tiger or the Tasmanian wolf...

, and the Pyrenean Ibex
Pyrenean Ibex
The Pyrenean Ibex is an ibex, one of the two extinct subspecies of Spanish Ibex. The subspecies once ranged across the Pyrenees in France and Spain and the surrounding area, including the Basque Country, Navarre, north Aragon and north Catalonia. A few hundred years ago they were numerous, but by...

. In order for such a program to succeed, a sufficient number of 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
Bioethics
Bioethics is the study of controversial ethics brought about by advances in biology and medicine. Bioethicists are concerned with the ethical questions that arise in the relationships among life sciences, biotechnology, medicine, politics, law, and philosophy....

 and philosophical
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

 objections have been raised, the cloning of extinct creatures seems a viable outcome of the continuing advancements in our science and technology.

In 2003, scientists attempted to clone the extinct Pyrenean Ibex
Pyrenean Ibex
The Pyrenean Ibex is an ibex, one of the two extinct subspecies of Spanish Ibex. The subspecies once ranged across the Pyrenees in France and Spain and the surrounding area, including the Basque Country, Navarre, north Aragon and north Catalonia. A few hundred years ago they were numerous, but by...

 (C. p. pyrenaica). This initial attempt failed; of the 285 embryos reconstructed, 54 were transferred to 12 mountain goats and mountain goat
Mountain goat
The Mountain Goat , also known as the Rocky Mountain Goat, is a large-hoofed mammal found only in North America. Despite its vernacular name, it is not a member of Capra, the genus of true goats...

-domestic goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...

 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.

The concept of cloning extinct species was thought to be first popularized by the successful novel and subsequent film Jurassic Park
Jurassic Park (film)
Jurassic Park is a 1993 American science fiction adventure film directed by Steven Spielberg. The film is based on the novel of the same name by Michael Crichton. It stars Sam Neill, Laura Dern, Jeff Goldblum, Richard Attenborough, Martin Ferrero, and Bob Peck...

, though it may have been first used in John Brosnan
John Brosnan
John Raymond Brosnan was an Australian writer of both fiction and non-fiction works based around the fantasy and science fiction genres. He was born in Perth, Western Australia, and died in South Harrow, London, from acute pancreatitis...

's 1984 novel Carnosaur
Carnosaur (novel)
Carnosaur is a horror novel written by Australian author John Brosnan, under the pseudonym of Harry Adam Knight. A film adaptation was made in 1993 by Adam Simon....

, then in F. Paul Wilson's
F. Paul Wilson
Francis Paul Wilson is an American author, primarily in the science fiction and horror genres. His debut novel was Healer . Wilson is also a part-time practicing family physician. He made his first sales in 1970 to Analog while still in medical school , and continued to write science fiction...

 1989 novel Dydeetown World, and later in Piers Anthony's
Piers Anthony
Piers Anthony Dillingham Jacob is an English American writer in the science fiction and fantasy genres, publishing under the name Piers Anthony. He is most famous for his long-running novel series set in the fictional realm of Xanth.Many of his books have appeared on the New York Times Best...

 1990 novel Balook, which featured the resurrection of a Baluchitherium.

See also


  • Endling
    Endling
    An endling is the name given to an individual animal that is the last of its species. Once the endling dies, the species becomes extinct."On 7 September 1936 an endling died in Hobart Zoo...

  • Extinction risk from global warming
  • Gene pool
    Gene pool
    In population genetics, a gene pool is the complete set of unique alleles in a species or population.- Description :A large gene pool indicates extensive genetic diversity, which is associated with robust populations that can survive bouts of intense selection...

  • Genetic erosion
    Genetic erosion
    Genetic erosion is a process whereby an already limited gene pool of an endangered species of plant or animal diminishes even more when individuals from the surviving population die off without getting a chance to meet and breed with others in their endangered low population.Genetic erosion occurs...

  • Genetic pollution
    Genetic pollution
    Genetic pollution is a controversial term for uncontrolled gene flow into wild populations. This gene flow is undesirable according to some environmentalists and conservationists, including groups such as Greenpeace, TRAFFIC, and GeneWatch UK.-Usage:...

  • Genocide
    Genocide
    Genocide is defined as "the deliberate and systematic destruction, in whole or in part, of an ethnic, racial, religious, or national group", though what constitutes enough of a "part" to qualify as genocide has been subject to much debate by legal scholars...

  • Habitat fragmentation
    Habitat fragmentation
    Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...

  • IUCN Red List
    IUCN Red List
    The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...

  • IUCN Red List of extinct species
    IUCN Red List of extinct species
    On 29 January 2010, the IUCN Red List of Threatened Species identified 842 extinct species, subspecies and varieties, stocks and...

     for a list by taxonomy
    Taxonomy
    Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

  • Ecological importance of bees
  • List of extinct animals
  • List of extinct plants
  • Living Planet Index
    Living Planet Index
    The Living Planet Index is an indicator of the state of global biological diversity, based on trends in vertebrate populations of species from around the world....

  • Mass extinction
  • Overexploitation
    Overexploitation
    Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Sustained overexploitation can lead to the destruction of the resource...

  • Red List Index
    Red List Index
    The Red List Index , based on the IUCN Red List of Threatened Species, is an indicator of the changing state of global biodiversity. It defines the conservation status of major species groups, and measures trends in extinction risk over time...

  • Refugium (population biology)
  • Speciation
    Speciation
    Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...

  • Timeline of extinctions
    Timeline of extinctions
    The timeline of extinctions is an historical account of species that have gone extinct during the time that modern humans have occupied the earth....

  • Voluntary Human Extinction Movement
    Voluntary Human Extinction Movement
    The Voluntary Human Extinction Movement, or VHEMT , is a movement which calls for the voluntary gradual self-extinction of the human species through abstaining from reproduction. VHEMT's motto is "May we live long and die out."...

  • Dinosaurs

External links