Comparison of Red List classes above
and NatureServe status below
|Part of a series on|
Extinction is the termination of a
More than 99% of all species that ever lived on Earth, amounting to over five billion species, are estimated to have died out. It is estimated that there are currently around 8.7 million species of eukaryote globally, and possibly many times more if microorganisms, like bacteria, are included. Notable extinct animal species include non-avian dinosaurs, saber-toothed cats, dodos, mammoths, ground sloths, thylacines, trilobites, and golden toads.
Through evolution, species arise through the process of speciation—where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche—and species become extinct when they are no longer able to survive in changing conditions or against superior competition. The relationship between animals and their ecological niches has been firmly established. 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 and scientists have become 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
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, but likely many more. The main cause of the extinctions is the destruction of natural habitats by human activities, such as cutting down forests and converting land into fields for farming.
A dagger symbol (†) placed next to the name of a species or other taxon normally indicates its status as extinct.
Examples of species and subspecies that are extinct include:
- Chinese paddlefish (last seen in 2003; declared extinct in 2022)
- Great auk (last confirmed pair was killed in the 1840s)
- Thylacine (the last thylacine killed in the wild was shot in 1930; the last captive tiger lived in Hobart Zoo until 1936)
- Kauai O'o (last known member was heard in 1987; the entire Mohoidae became extinct with it)
- Spectacled cormorant (last known members were said to live in the 1850s)
- Incasdied in captivity in 1918; declared extinct in 1939)
- Passenger pigeon (last known member named Martha died in captivity in 1914)
- Tasmanian emu (the last claimed sighting of the emu was in 1839)
- Japanese Sea Lion(the last confirmed record was a juvenile specimen captured in 1974)
- Schomburgk's deer (became extinct in the wild in 1932; the last captive deer was killed in 1938)
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
Currently, an important aspect of extinction is human attempts to preserve critically endangered species. These are reflected by the creation of the
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
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.
Far more recent possible or presumed extinctions of species which may turn out still to exist include the
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
Assessing the relative importance of genetic factors compared to environmental ones as the causes of extinction has been compared to the debate on
Human-driven extinction started as humans migrated out of Africa more than 60,000 years ago.
Genetics and demographic phenomena
If adaptation increasing population fitness is slower than environmental degradation plus the accumulation of slightly deleterious mutations, then a population will go extinct. 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
Extinction sometimes results for species evolved to specific ecologies
The gene pool of a
Habitat degradation is currently the main anthropogenic cause of species extinctions. The main cause of habitat degradation worldwide is agriculture, with
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.
Predation, competition, and disease
In the natural course of events, species become extinct for a number of reasons, including but not limited to: extinction of a necessary host, prey or pollinator,
Coextinction refers to the loss of a species due to the extinction of another; for example, the extinction of
Extinction as a result of
Sexual selection and male investment
Studies of fossils following species from the time they evolved to their extinction show that species with high sexual dimorphism, especially characteristics in males that are used to compete for mating, are at a higher risk of extinction and die out faster than less sexually dimorphic species, the least sexually dimorphic species surviving for millions of years while the most sexually dimorphic species die out within mere thousands of years. Earlier studies based on counting the number of currently living species in modern taxa have shown a higher number of species in more sexually dimorphic taxa which have been interpreted as higher survival in taxa with more sexual selection, but such studies of modern species only measure indirect effects of extinction and are subject to error sources such as dying and doomed taxa speciating more due to splitting of habitat ranges into more small isolated groups during the habitat retreat of taxa approaching extinction. Possible causes of the higher extinction risk in species with more sexual selection shown by the comprehensive fossil studies that rule out such error sources include expensive sexually selected ornaments having negative effects on the ability to survive natural selection, as well as sexual selection removing a diversity of genes that under current ecological conditions are neutral for natural selection but some of which may be important for surviving climate change.
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.
According to a 1998 survey of 400 biologists conducted by
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
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,
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.
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.
Belgian scientists have proposed a potential explanation for the mass extinction of dinosaurs on Earth, suggesting that dust played a significant role. Around 66 million years ago, an asteroid struck the Earth off the coast of Mexico, marking the conclusion of the Cretaceous period. While it is widely accepted that dinosaurs near the impact site would not have survived, scientists were inquisitive about the fate of the rest of the dinosaur population. To address this question, researchers at the Royal Observatory of Belgium conducted computer-generated simulations, digitally recreating events that transpired after the asteroid's impact.
The asteroid that impacted Earth 66 million years ago formed the Chicxulub Crater, located beneath the Yucatán Peninsula off the Mexican coast. Scientific studies indicate that the Chicxulub asteroid released sulfur-based gases and a significant amount of silicate dust into Earth's atmosphere. This impact subsequently initiated volcanic eruptions and widespread wildfires worldwide, leading to the release of soot and carbon dioxide into the air. These combined effects resulted in a prolonged period of darkness caused by the airborne particles, creating a "winter" that endured for approximately 15 years.
According to the researchers, this "impact winter" is accountable for the extinction of 75% of Earth's plant and animal species. The hazy atmosphere obscured sunlight, preventing plants from conducting photosynthesis, their process for generating energy and growth. Consequently, a majority of plant life perished, resulting in a scarcity of food for herbivorous dinosaurs. As plant-eating dinosaurs dwindled, it also led to a decrease in the available food supply for carnivorous dinosaurs.
Human attitudes and interests
Extinction is an important research topic in the field of
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
Governments sometimes see the loss of native species as a loss to
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.
- The smallpox virus is now extinct in the wild, although samples are retained in laboratory settings.
- The infected domestic cattle, is now extinct in the wild.
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.
Some, such as Harvard geneticist
In 2003, scientists tried to clone the extinct Pyrenean ibex (C. p. pyrenaica).
- Empty forest
- Extinction: The Facts (2020 documentary)
- Habitat fragmentation
- Lists of extinct animals
- List of extinct birds
- Living Planet Index
- Our Final Hour
- Refugium (population biology)
- Sepilok Orang Utan Rehabilitation Centre
- The Sixth Extinction: An Unnatural History (2014 book)
- Voluntary Human Extinction Movement
- Novacek, Michael J. (8 November 2014). "Prehistory's Brilliant Future". The New York Times. Archived from the original on 29 December 2014. Retrieved 25 December 2014.
- "Researchers find that Earth may be home to 1 trillion species". National Science Foundation. 2 May 2016. Archived from the original on 4 May 2016. Retrieved 6 May 2016.
- "Species disappearing at an alarming rate, report says". NBC News. 17 November 2004. Archived from the original on 9 February 2022. Retrieved 9 February 2022.
Moreover, we have unleashed a mass extinction event, the sixth in roughly 540 million years, wherein many current life forms could be annihilated or at least committed to extinction by the end of this century.
- Watts, Jonathan (6 May 2019). "Human society under urgent threat from loss of Earth's natural life". The Guardian. Archived from the original on 14 June 2019. Retrieved 6 May 2019.
- Plumer, Brad (6 May 2019). "Humans Are Speeding Extinction and Altering the Natural World at an 'Unprecedented' Pace". The New York Times. Archived from the original on 14 June 2019. Retrieved 6 May 2019.
- "Media Release: Nature's Dangerous Decline 'Unprecedented'; Species Extinction Rates 'Accelerating'". Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. 6 May 2019. Archived from the original on 14 June 2019. Retrieved 6 May 2019.
- Briggs, Helen (8 July 2022). "Unsustainable logging, fishing and hunting 'driving extinction'". BBC. Archived from the original on 1 August 2022. Retrieved 2 August 2022.
- "'Frightening' number of plant extinctions found in global survey". The Guardian. 10 June 2019. Archived from the original on 22 April 2021. Retrieved 11 June 2019.
- Maas, Peter. "Extinct in the Wild" The Extinction Website. URL accessed January 26 2007. Archived February 16, 2007, at the Wayback Machine
- Mosbergen, Dominique (16 October 2018). "Mammals Will Still Be Recovering From Human Destruction Long After We're Gone". HuffPost. Archived from the original on 9 February 2022. Retrieved 9 February 2022.
- King, Michael; Mulligan, Pamela; Stansfield, William (2014). A Dictionary of Genetics (8th ed.). Oxford University Press.
- ""Discovery" of the Coelacanth". Archived from the original on 21 January 2013. Retrieved 2 March 2013.
- Platt, John R. (21 February 2013). "4 Extinct Species That People Still Hope to Rediscover". Scientific American Blog Network. Archived from the original on 9 February 2022. Retrieved 9 February 2022.[self-published source?]
- Johns, David; Crist, Eileen; Sahgal, Bittu, eds. (2022). "Ending the Colonization of the Non-Human World". Biological Conservation.
- Lewis, Sophie (9 September 2020). "Animal populations worldwide have declined by almost 70% in just 50 years, new report says". CBS News. Archived from the original on 10 September 2020. Retrieved 22 October 2020.
- "Glossary: definitions from the following publication: Aubry, C., R. Shoal and V. Erickson. 2005. Grass cultivars: their origins, development, and use on national forests and grasslands in the Pacific Northwest. USDA Forest Service. 44 pages, plus appendices.; Native Seed Network (NSN), Institute for Applied Ecology, 563 SW Jefferson Ave, Corvallis, OR 97333, USA". Archived from the original on 22 February 2006.
- "Australia's state of the forests report" (PDF). 2003. p. 107. Archived from the original (PDF) on 13 March 2011.
"Genetic diversity" (PDF). 2003. p. 104. Archived from the original (PDF) on 13 March 2011. Retrieved 30 May 2010.
In other words, greater genetic diversity can offer greater resilience. In order to maintain the capacity of our forests toadaptto future changes, therefore, genetic diversity must be preserved
- Lee, Anita. "The Pleistocene Overkill Hypothesis Archived October 14, 2006, at the Wayback Machine." University of California at Berkeley Geography Program. Retrieved January 11, 2007.
- Bhattacharya, Shaoni (7 January 2004). "Global warming threatens millions of species". New Scientist. Archived from the original on 21 April 2010. Retrieved 28 May 2010.
the effects of climate change should be considered as great a threat to biodiversity as the "Big Three"—habitat destruction, invasions by alien species and overexploitation by humans.
- Handwerk, Brian; Hendwerk, Brian (April 2006). "Global Warming Could Cause Mass Extinctions by 2050, Study Says". National Geographic News. Archived from the original on 12 June 2017. Retrieved 27 October 2017.
- Ritchie, Hannah (20 April 2021). "Wild mammals have declined by 85% since the rise of humans, but there is a possible future where they flourish". Our World in Data. Retrieved 19 April 2023.
- American Museum of Natural History. "National Survey Reveals Biodiversity Crisis – Scientific Experts Believe We are in the Midst of the Fastest Mass Extinction in Earth's History Archived 10 April 2012 at the Wayback Machine". Retrieved September 20, 2006.
- Wilson, E.O. (30 April 2012). ""E. O. Wilson wants to know why you're not protesting in the streets"". Grist (Interview). Interviewed by Lisa Hymas. Archived from the original on 4 November 2017. Retrieved 16 January 2014. E.O. Wilson repeats his estimation in 2012.
- Carrington D (2 February 2021). "Economics of biodiversity review: what are the recommendations?". The Guardian. Archived from the original on 24 May 2022. Retrieved 21 December 2021.
- Dasgupta, Partha (2021). "The Economics of Biodiversity: The Dasgupta Review Headline Messages" (PDF). UK government. p. 1. Archived (PDF) from the original on 20 May 2022. Retrieved 21 December 2021.
Biodiversity is declining faster than at any time in human history. Current extinction rates, for example, are around 100 to 1,000 times higher than the baseline rate, and they are increasing.
- Sutter, John D. (12 December 2016). "How to stop the sixth mass extinction". CNN. Archived from the original on 13 December 2016. Retrieved 3 January 2017.
- Graham, Chris (11 July 2017). "Earth undergoing sixth 'mass extinction' as humans spur 'biological annihilation' of wildlife". The Telegraph. Archived from the original on 11 January 2022. Retrieved 23 July 2017.
- Greenfield, Patrick (13 January 2020). "UN draft plan sets 2030 target to avert Earth's sixth mass extinction". The Guardian. Archived from the original on 24 February 2021. Retrieved 14 January 2020.
- Yeung, Jessie (14 January 2020). "We have 10 years to save Earth's biodiversity as mass extinction caused by humans takes hold, UN warns". CNN. Archived from the original on 15 February 2021. Retrieved 14 January 2020.
- Cohen, Li (15 September 2020). "More than 150 countries made a plan to preserve biodiversity a decade ago. A new report says they mostly failed". CBS News. Archived from the original on 15 May 2022. Retrieved 23 September 2020.
- Yeung, Jessie (16 September 2020). "The world set a 2020 deadline to save nature but not a single target was met, UN report says". CNN. Archived from the original on 15 May 2022. Retrieved 23 September 2020.
- Weston, Phoebe (13 January 2021). "Top scientists warn of 'ghastly future of mass extinction' and climate disruption". The Guardian. Archived from the original on 13 January 2021. Retrieved 19 January 2021.
- "Extinctions: Georges Cuvier". evolution.berkeley.edu. Archived from the original on 29 April 2017. Retrieved 4 May 2017.
- Rowland, Stephen (2009). "Thomas Jefferson, extinction, and the evolving view of Earth history in the late eighteenth and early nineteenth centuries". GSA Memoirs. 203: 225–246. Archived from the original on 1 September 2015. Retrieved 5 May 2017.
- Lyells, Charles (1854). The Principles of Geology or, The Modern Changes of the Earth and its Inhabitants Considered as Illustrative of Geology. New York: Appleton Co. Archived from the original on 25 October 2016. Retrieved 5 May 2017.
- Bressan, David (17 August 2011). "On the Extinction of Species". Scientific American Blog Network. Archived from the original on 22 December 2017. Retrieved 5 May 2017.[self-published source?]
- "The Lost World". The New Yorker. 9 December 2013. Archived from the original on 3 February 2023. Retrieved 9 February 2022.
- "Dust could be responsible for wiping out 75% of all species on Earth". BBC Newsround. 2 November 2023. Retrieved 5 November 2023.
- Einhorn, Catrin (27 January 2021). "Shark Populations Are Crashing, With a 'Very Small Window' to Avert Disaster". The New York Times. Archived from the original on 31 January 2021. Retrieved 31 January 2021.
- Walsh, Bruce. Extinction Archived 1997-08-02 at the Wayback Machine. Bioscience at University of Arizona. Retrieved July 26, 2006.
- Committee on Recently Extinct Organisms. "Why Care About Species That Have Gone Extinct? Archived 13 July 2006 at the Wayback Machine". Retrieved July 30, 2006.
- International Programme on Chemical Safety (1989). "DDT and its Derivatives – Environmental Aspects Archived 27 September 2006 at the Wayback Machine". Environmental Health Criteria 83. Retrieved September 20, 2006.
- "DDT and its derivatives (EHC 9, 1979)". Archived from the original on 25 February 2021. Retrieved 26 September 2020.
- Drewry, Rachel. "Ecotourism: Can it save the orangutans? Archived February 16, 2007, at the Wayback Machine" Inside Indonesia. Retrieved January 26, 2007.
- The Wildlands Project Archived November 22, 2005, at the Wayback Machine. Retrieved January 26, 2007.
- Alliance for Zero Extinctions Archived April 23, 2011, at the Wayback Machine. Retrieved January 26, 2007.
- "Smallpox". WHO Factsheet. Archived from the original on 21 September 2007.
- "Polio cases in the world in 2015". The Global Polio Eradication Initiative. Archived from the original on 19 February 2016. Retrieved 17 February 2016.
- "This Species is Close to Extinction and That's a Good Thing". Time. 23 January 2015. Archived from the original on 24 February 2016. Retrieved 17 February 2016.
- Olivia Judson (25 September 2003). "A Bug's Death". The New York Times. Archived from the original on 6 March 2016. Retrieved 17 February 2016.
- Paulson, Steve (4 April 2016). "Why a famous biologist wants to eradicate killer mosquitoes". The World from PRX. Archived from the original on 9 February 2022. Retrieved 9 February 2022.
- A. Zitner (24 December 2000). "Cloned Goat Would Revive Extinct Line". Los Angeles Times. Archived from the original on 25 August 2011. Retrieved 17 May 2010.
- Nicholas wade (19 November 2008). "Regenerating a Mammoth for $10 Million". The New York Times. Archived from the original on 12 March 2017. Retrieved 17 May 2010. The cell could be converted into an embryo and brought to term by an elephant, a project he estimated would cost some $10 million. "This is something that could work, though it will be tedious and expensive,"
- Steve Connor (2 February 2009). "Cloned goat dies after attempt to bring species back from extinction". The Independent. London. Archived from the original on 13 October 2017. Retrieved 17 May 2010.
- Gray, Richard; Dobson, Roger (31 January 2009). "Extinct ibex is resurrected by cloning". Telegraph. London. Archived from the original on 11 January 2022.
- PMID 35757873.
- Elizabeth Pennisi (9 March 2022). "Bringing back the woolly mammoth and other extinct creatures may be impossible". Science.
- Pelley, Scott (1 January 2023). "Scientists say planet in midst of sixth mass extinction, Earth's wildlife running out of places to live". CBS News.