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Extinction

Extinction

Humans are the only species aware of not only of their own eventual personal deaths but of their collective demise as well. This latter insight came late in human historya product of evolutionary theory and of paleontological and archaeological research.

The West still deals with the twin "cognitive shocks" from the mid-nineteenth-century discoveries that extinction was the fate both of creatures very much like human beings and of cultures as articulate as those in the West, whose people can still speak directly to Western civilization because of their writing systems. On top of these are the twentieth century's scientific end-of-world scenarios, predicting the inevitable extinction of not only all life forms on Earth when the sun goes supernova, but of the entire universe, when entropy is complete and the last nuclear fires flicker out.

Since WWIIparticularly following the publications of Rachel Carson's Silent Spring (1962) and Paul Ehrlich's Population Bomb (1968)sensitivities toward extinction have heightened with cold war fears of nuclear war, the obvious diminishment and degradation of the natural order owing to industrialization and burgeoning human numbers, and with millennial apocalyptic fears. With increasing regularity the news brings scientific findings of global warming, of a rapidly growing list of endangered and newly extinct life forms, of "earth-killer" asteroids lurking nearby, and of lethal pollutants in the air, soil, and water. The polar ice caps are melting as are the famed snows of Kilimanjaro. The blubber of orcas from the American Pacific Northwest found to contain PCB (polychlorinated biphenyls) concentrations up to 500 times greater than those found in humans. In the extreme, such phenomena are interpreted as symptoms of the beginning of the end of not only the planet's entire ecosystem but human beings as well.

Extinction as the consequence of natural selection and the fate of the "unfit" was to become the metaphor for understanding not only natural but social phenomena as well, whether it be the success or failures of businesses or of entire cultural orders. It also found expressions in the justifications for war, exploitation, and forced sterilizations and genocides of human populations.

Scientific Perspectives

The law of life from scientific perspectives holds that all life forms, ecosystems, planets, stars, and galaxies come and go. Personal death and collective extinction are the debts for lifeon the individual, species, genus, family, order, class, and phyla levels. Since life first appeared on Earth 3.5 billion years ago, over 10 billion species have come into existence (and this figure is the roughest of estimates). Somewhere between 10 million and 30 million species (of which scientists have counted only about one-eighth) currently reside on the planet. In other words, for every 1,000 species that have ever existed probably fewer than 10 are alive in the twenty-first century.

Challenging the conventional idea that "species were immutable productions," the naturalist Charles Darwin wrote On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, explaining how life is a continuous process of modification and current life forms are descendants of extinct ancestral species. Natural selection is "the process by which genes change their sequences" (Ridley 2000, p. 35), by which those organisms best adapted to their environment survive to pass on their genetic code while those (previously "successful") life forms unable to make adaptive modifications to varying conditions perish. Species' billing on the stage of life is relatively short in terms of geologic time, with most becoming extinct within a few million years after their evolution. Most leave no related descendant species but rather become evolutionary dead ends.

Life is a continuous process of extinction and diversification, where only the fittest life forms survive in a world where, according to Darwin, they are "bound together by a web of complex relations" (1963, p. 54). Central to these "relations" are the ecological niches, the millions of different "fits" and functional interdependencies that plants and animals have with each other in their ecosystem. While various creatures may share a habitat, generally a niche can only be occupied by one species of animal or plant. When two different organisms compete for a particular niche, one will invariably lose out. If a niche should become empty, such as through extinction, other life forms will rush in and compete to fill the vacuum. In the case of a mass die-off, evolutionary explosions of new life forms occur as plants and animals adapt to take advantage of the abundance of newly opened niches.

Another factor affecting the rate of extinction and differentiation of life forms is the extent of biodiversity in an ecosystem. These natural systems comprising the biosphere do such things as cycle oxygen and carbon, purify the water, and decompose waste. Diminish the genetic variation in individual species and they become more vulnerable to extinction. Homogenize the biotas in human-dominated ecosystems and biodisparity declines.

The diversity of life used to be considerably richer than is the case in the twenty-first century. For instance, based on the fossil record of the Cambrian Period over 500 million years ago, there may have been four to five times the number of phyla as exist today. Given present trends, this multiplier may be even greater in the near future as the site of the planet's greatest biodiversity, the tropical forests where between 50 and 90 percent of species reside, are rapidly disappearing. Worldwide, tropical forests four times the size of Switzerland are cut down annually, replaced with fields for cash crops and to make room for burgeoning human populationswhich, in turn, pollute the water and land, further diminishing the variety and size of natural habitats.

Though humans may be one of the only species to have adapted to nearly all environments on Earth, their existence nevertheless remains dependent upon the complex systems of inter-dependent life forms.

Periodic Mass Extinctions

The rate of extinction is far from constant. In addition to the routine processes of Darwin's natural selection, various terrestrial and extraterrestrial catastrophes have profoundly altered the course of evolution. Paleontologists report historic cycles of mass death, dooming or marginalizing a portion of previously well-adapted species, followed by steep increases in the diversity of new life forms.

At least five periods of mass extinction have been identified, eliminating over half of the world's species at the time of their occurrence (although, in total, causing less than 5% of all extinctions). Scientific debate centers not on whether these mass die-offs have occurred but rather if they happened quickly, such as due to asteroid impact or a nearby star going supernova, or more slowly, such as due to glaciations, volcanic activity, changes in seawater oxygen or salinity, or epidemics. The time required for the species diversification to rebound to pre-catastrophe levels is estimated to be roughly 25 million years.

Asteroids are suspected in at least the three most recent mass die-offs. Most publicized is the suspected 10-kilometer-wide meteorite that slammed into what's now the Gulf of Mexico and the Yucatán Peninsula 65 million years ago, leaving the 180-kilometer-wide Chicxulub Crater, wiping out the dinosaurs, and ending the Cretaceous period. Another is believed to have concluded the Permian period with even more devastating results, when 250 million years ago some 96 percent of marine and 70 percent of land fauna disappeared. Ironically, shortly after Jurassic Park 's release, the world witnessed over twenty parts of Comet Shoemaker-Levy collide with Jupiter. At least nine of these could have been Earth-killers, one forming a crater the planet could easily fit within. As of 2000, according to the British National Space Center, 284 asteroids have been located with the size and orbits to be deemed "potentially hazardous" to Earth.

There is evidence that mass extinctions may number in the dozens, with up to three-quarters of all species disappearing every 26 to 30 million years. One explanation for this cyclical regularity is the possible existence of a companion star to the sun. Called Nemesis, when this star reaches its perigee every 26 million years, it shakes loose and hurls a comet storm from the Oort cloud on the fringe of Earth's solar system. Every 50,000 years or so, for over a period of 2 million years, one of these comets collides with Earth, producing ecological catastrophes that lead to periodic global deaths.

Among biologists there is broad consensus that human beings are witnessing the sixth mass extinction, with anywhere from 10,000 to 20,000 species of animals and plants disappearing annuallya rate conservationists estimate to be 1,000 to 10,000 times greater than would be the case under natural conditions. A 1998 American Museum of Natural History survey of 400 experts in the biological sciences found approximately 70 percent expecting up to one in five of all living species on the planet disappearing within thirty years. What makes this different from the five other known periods of mass extinctionwhich were linked with asteroids, ice ages, and volcanoesis the human complicity involved. We are death and are responsible for this "species holocaust" (Day 1981). In a sense, all creatures have become our miner's canaries and their disappearance means that the

The five greatest mass extinctions
  Ordivician-silurian Late Devonian Permian-triassic Late Triassic Final Cretaceous
When Occurred 439 million years ago 365 million years ago 251 million years ago 199214 million years ago 65 million years ago
Casualties Up to estimated 85% species and 4560% of marine genuses killed. 7080% of all species and 30% of families vanish; marine life more decimated than freshwater and land fauna. Most devastating of all, eliminating 8590% of all marine and land vertebrate species, 95% of marine species. End of trilobites and many trees. More than three quarters of all species and one quarter of families disappear. End of mammal-like reptiles and eellike conodonts, leaving mainly dinosaurs. 47% of marine genuses and 18% of land vertebrates wiped out, including the dinosaurs, leaving mainly turtles, lizards, birds, and mammals.
Hypothesized Cause(s) Unusually fast plate movement; glaciation leading to sharp de- clines in sea levels. Unknown if one cat- astrophic event or several smaller onespossibly large asteroid or asteroid shower over time; possible glaciation and lethal temperature de- clines; oceanic anoxia (oxygen-lacking) Possible asteroid; volcanic eruptions; dropping sea levels and oceanic anoxia Little known but suspected fall in sea level, oceanic anoxia, major increase in rainfall. Possible comet showers or asteroid impact. Suspected asteroid 10 km. in diameter hitting near Yucatán peninsula, coinciding with Siberian eruptions and dramatic climatic cooling.
SOURCE: Adapted from A. Hallam, and P. B. Wignall, 1997; David Raup, and John J. Sepkosi Jr., 1986; and Lee Siegel, 2000.

health of the ecosystem is endangered and that we are running out of biological room

Human complicity in the Pleistocene extinction of large game animals remains a subject of debate, as there is a coincidence of receding glaciers, human migrations, and the extinction of many large game animals. The moa, a 400-pound flightless bird that thrived in New Zealand until about the year 1250, totally disappeared within 60 to 120 years of the first human arrival. Using fire as a weapon and tool, these settlers also burned into extinction an entire forest that was to become grassland. Similarly, woolly mammoths, camels, horses, sabertoothed tigers, and more than 120 other Pleistocene mammalian species all disappeared within a few hundred years after humans arrived in the New World roughly 11,000 to 13,000 years ago.

Perhaps the most poignant of recent extinctions is the passenger pigeon, which was to be hunted into oblivion. At the beginning of the American Civil War, this was one of the most successful bird species in North America, comprising an estimated 40 percent of the entire bird population. In 1870, a single flock one mile wide and 320 miles long flew over Cincinnati. In 1974 the last surviving pigeon died in that city's zoo. As of 2001, conservationists estimated that one in every six species of birds is in decline on the continent and could wane by half by the year 2030.

But the major cause of animal demise is the destruction of natural habitats as human populations exploded, tripling just between 1930 to 2000, leading to urban sprawl, overfishing, overgrazing, deforestation, overuse of pesticides and herbicides, strip mining, and pollution of fresh water systems. Human introduction of non-native "invasive" species has also taken its toll. Fungus carried by North American ships, for instance, led to the Irish potato famine. Of those who fled migrated to Australia with rabbits and cats, many of which went wild and decimated indigenous plants and animals.

In Africa, the deserts annually expand thousands of square miles as a rapidly growing human population strips its indigenous vegetation for fuel (wood remains the chief energy source for many of its inhabitants) and to make room for profitable crops or livestock. Here the removal of ground cover leads to a greater runoff of rain, reducing evaporation into the clouds and thereby contributing to the severity of the region's routine droughts.

The loss is not confined to wild, undomesticated plants and animals but includes domesticated ones as well. During the twentieth century, because of the rise of cash crops and farmers' cultivation for maximum yield, three-quarters of the genetic diversity of the world's agricultural crops was lost. Roughly half of all domestic animal breeds in Europe became extinct. Gone are about 6,000 apple varieties that grew on U.S. farms 100 years ago. In the mid-1990s, the United Nations Food and Agriculture Organization reported that nearly onequarter of the 3,882 breeds of 28 species of farm animals around the world were "at risk"meaning fewer than 1,000 females or 20 breeding males.

What worries experts most is the prospect that farmers will have a shrinking pool of breeds to draw upon to keep up with changing soil conditions, pests, and new diseases.

In other words, concerns are for preserving biodiversity, particularly in light of cash crops and humanity putting its proverbial eggs in fewer and fewer baskets.

Two groups of extinctions have intrigued humans over the past two centuries: the demise of the dinosaurs and of human ancestors. Over the final two decades of the twentieth century there was considerable research and public interest in the instantaneous (in geological time) demise 65 million years ago of dinosaurs, among the most successful (in terms of their length of reign on Earth) animals known. This interest coincided with the cold war, which was not coincidental. Humanity's ability to equally quickly make itself extinct through thermonuclear devices became a widely accepted fact. Another factor heightening cultural receptivity was the rapid disappearance of its own social pastfor example, old crafts, buildings, social etiquetteproducing a sense of irretrievable loss. Modernity had come to mean impermanence in a culture of obsolescence where the only certainty had become change.

Unearthed in a quarry by Germany's river Neander in 1856 as an unusual humanlike skeleton with a beetled browed skull. This discovery of the Neanderthals, a tool-making creature very similar to Homo sapien, ultimately led to the unsettling insight that extinction has also been the fate of all branches of the hominid family and of the Homo genus except for human sapiens. Modern humans' complicity in the demise of these archaic humans remains a matter of speculation, with evidence indicating that humans shared the planet with at least the Neanderthals as recently as 26,000 years ago in Europe.

Social Reactions to Extinctions of the Natural Order

Only in modern times has there been the realization that the planet's living resources are neither infinite nor always replenishableand the scientific understanding of how precarious the interdependencies between all life forms are. People were surprised in the 1860s when human artifacts were first found with extinct species in Europe. Severely challenged were biblical allusions to some "steady-state" or regenerative natural order, the fauna descendents of passengers on Noah's ark, all of which were to be dominated by humans. Only later did people come to learn how the overkilling of "keystone species" could lead to an environmental collapse and the extinction of even nonhunted creatures.

For those living within largely manmade environments and within a highly individualistic culture, appreciation of life's thorough interdependencies comes hard. Further, Cartesian conceptions of human's biological essencethe body-as-machine metaphor that has long predominated in medicinecomplicates more holistic understandings.

Limited is any acknowledgment of human complicity in the sixth mass extinction. According to 1993 and 1994 surveys of the American adult public conducted by the National Opinion Research Center, only 16 percent of American adults believe it is "definitely true" that "human beings are the main cause of plant and animal species dying out." Four in ten agree with the statement, "We worry too much about the future of the environment and not enough about prices and jobs today." And only one in three was "very" or "fairly" willing to accept cuts in his or her standard of living in order to protect the environment.

The perspective from the scientific community is less benign. Several scientists have likened human effects on the ecosystem to cancer. If people take the Gaia perspective of Earth functioning like one mega living organism, aerial views can show striking similarity to melanomas attacking healthy tissue.

The Economics of Extinction

The rise of the world economic order and its capitalist structure has accelerated the decimation of species. If, as Martin Luther King Jr. observed in 1967, capitalism has a tendency to treat profit motives and property rights as more important than people, one can easily surmise the importance it gives to the natural order. The system produces a bias toward short-term gains at the cost of long-term consequences. As mentioned, cash crops in the international marketplace have accelerated the end of many species. The price tag of the resultant reduction of biodiversity rarely enters into the market system's cost-benefit equation. This absence is due, in part, to the fact that people really don't know how to calculate the worth of such endangered species as snail darters or white spotted owls.

In 1976 Daniel Bell wrote of the cultural contradictions of capitalism, perceiving them as seeds for changeor the death knell for entire social orders. One contradiction of relevance here is the economics of extinction, how the growing scarcity of a life form can increase its value and thereby accelerate its disappearance. For instance, in the 1980s when the market value of rhino horns exceeded the per ounce value of silver by ten times, this reduced the number of black rhinos in the Tanzanian Ngorongoro Crater from seventy-six to twenty-six in a single year. Pathetically, as their numbers declined the value of their parts hyperinflated, encouraging further exploitation. Another contradiction is how farmers will have a shrinking pool of breeds to draw upon to keep up with changing soil conditions, pests, and new diseases.

With the remnants of endangered species increasingly likely to only be preserved within zoos, research institutes, and parks, matters of cost and utility enter. Consider, for instance, the perspective of zoos. To garner public support, animal collections must attract audiences. The most popular animals are often those that are "cute," furry, and large-eyed. Consequently, with time, Darwin's thesis of the survival of the fittest may have to be modified to be the survival of the cutest, like the black and white colobus or the arctic seal. Also saved will be those creatures that enhance humankind's own longevity, such as apes or pigs for xenotransplantations. Concerns over the loss of the tropical rain-forests are often expressed in terms of human needs. One-quarter of prescription drugs are extracted from plants, including 70 percent of anti-cancer agents, and most of these come from tropical forestswhere less than 1 percent of the flora has been examined for its pharmacological utility.

The Politics of Extinction

At the beginning of the twenty-first century, decisions as to whether the needs of humans ultimately outweigh those of endangered species are largely the monopoly of political regimes. However, the planet's greatest biodiversity largely exists within developing nations where fertility rates are the highest, people the poorest, population pressures on nature the greatest, and unstable political regimes the least likely to resist powerful corporate and population encroachments on natural habitats.

Even in developed nations the accelerating rates of extinction have proven difficult to resist. The Green movement remains a minority voice. In the United States, awarenesses have become politicized. National surveys of 1993 and 1994 show Republicans are, for instance, 50 percent more likely than Democrats to disagree that "human beings are the main cause of plant and animal species dying out."

And just when environmental causes have entered the public consciousness, ecoterrorism (or threats thereof) has become a new weapon of disenfranchised and antiestablishment groups. During the summer of 2000, soon-to-be-laid-off chemical workers in Northern France dumped 3,000 liters of sulfuric acid into a tributary of the Meuse River.

Religion and Extinction

The notion that humans are programmed by only 40,000 or so genes and descended from a chain of earlier life forms profoundly challenged traditional religious beliefs that life and death are acts of divine will. From the scientific method came the possibility that the cosmos was not divinely constructed around humanity but rather is the product of random chance, and that the same natural forces controlling the fates (and inevitable extinctions) of animals shape human fate as well. Also assaulting people's sense of specialness is the evidence that human beings and their fellow thinking mammals are not the "fittest," as 95 percent of all animal species are invertebrates.

According to the Bible, God made human beings in his image and gave them dominion over all other creatures, whose existence was to serve their needs. To this day religion maintains this subordination of the natural order. When a random sample of Americans were asked whether "animals should have the same moral rights that human beings do," their agreement decreased with increasingly religiosity. When asked if "it is right to use animals for medical testing if it might save human lives," agreement increased with increasing religiosity.

Accused of causing "speciesism," Christianity has played a limited role in the war against extinction. Instead, the scientifically prompted ecological movement has come to assume some quasi-religious characteristics of its own.

The Battle against Extinction As Part of the War against Death

So why the extensive attempts to save the California condor, whose diet at its peak 1 million years ago consisted of such currently extinct creatures as dead mastodons, or the Kemp's Ridley turtle that, with a brain cavity the size of a pencil-width hole, is unable to learn a thing from experience and whose existence is totally hardwired? The reason may be largely symbolic.

The cultural war against death has expanded beyond the medical front to include battles against extinction in the natural orderand even resurrection of the extinct, as when in 2000 scientists awakened dormant 250-million-year-old bacteria encased in a salt crystal. Through human intervention, creatures extinct in the wild, like the Arabian oryx, are preserved in species preservation programs in zoos, ideally to be reintroduced to their native habitats. (In fact, there are cases where animals presumed extinct have been "discovered" in zoos, such as the Cape Lion, which was rediscovered in zoos in Novosibirsk, Serbia, and in Addis Ababa, Ethiopia.) In addition, genetic repositories, the contemporary "Noah's Arks," have been established by the Museum of Natural Science at Louisiana State University and the American Museum of Natural History to preserve in liquid nitrogen tissue samples from thousands of different creatures. In 2001, tissue frozen for eight years was used to successfully clone a gaur (a large type of cattle).

Perhaps in reaction to the extinction of the passenger pigeon, considerable press has been given to attempts to rescue the whooping crane from oblivion. This cause célèbre is a white crane with a seven-foot wingspan, mistakenly believed to be extinct in 1923. The victim of overhunting, its numbers had dwindled to about fifteen in 1941this, despite the Migratory Bird Treaty Act of 1918, which brought market hunting of the cranes and other migratory birds to an end, and the 1937 creation of the Arkansas National Wildlife Refuge on the Texas coast to protect the crane's last wintering ground. The U.S. Fish and Wildlife Service began a whooping crane recovery program in 1967, relying initially on captive breeding to build up the population. As of 2002, there are roughly 300 of the birds.

The Environmental Movement

In the broader cultural war against death, battles against extinction have assumed numerous fronts, such as conservation biology, gene banks, attempts to clone endangered species, and habitat restoration. Numerous new social solidarities have arisen, crosscutting the stratifications of class, gender, and age, in such groups as Friends of the Sea Otter, Sea Turtle Restoration Project, and Trees for the Future.

Growing concern over "ecocide" and "biological meltdown" has given rise to increasingly politicized environmental groups (Greenpeace, the Sierra Club, the National Wildlife Federation, Friends of the Earth, and various animal rights organizations). This social movement has quasi-religious trappings in its demands for ecojustice and concerns for leaving a legacy for future generations.

On the extreme fringe of this movement are the so-called ecoterrorists, such as the Earth Liberation Front and the Animal Liberation Front. Radical environmentalists, such as Finland's Pentti Linkola, see mass human death as the only way to save the planet's fragile ecosystem. This Voluntary Human Extinction Movement has the slogan "May We Live Long and Die Out." In addition to his hope for war, Linkola recommends ending capitalism, abolishing aid to the third world, and requiring mandatory abortions.

Cultural Extinction

Analogous to people's interest in extinct creatures is their curiosity about extinct civilizations, such as the mythical Atlantis or the Anasazis and Mayans of the New World, and the causes of these cultures' doom. As paleontologists study life forms of the past so archaeologists study past cultural orders, investigating whether their demise was due to avoidable factors with lessons that can be applied to the present. The archaeologist Richard Hansen, for instance, argues that deforestation produced an ecological disaster precipitating the collapse of the Maya civilization in approximately 800 C.E.To produce the stucco for their huge limestone pyramids, the Mayans leveled forests to fuel the hot fires required for transforming limestone into lime. Or was the fate of these doomed cultures sealed by unforeseen and uncontrollable calamities, such as epidemics, earthquake, or drought?

The human war against death extends from battles against the extinction of biological to cultural systems. Memes are to anthropologists what genes are to biologistscarriers of life's organizing principles, ways of doing this, that are passed down generation to generation. And as biologists worry about diminishing biodiversity, cultural scientists worry about the abatement of cultural diversity and endangered languages. Of the 6,800 languages spoken worldwide in 2001cultural DNA, if you willonly 600 are robust enough to be in existence at the end of the twenty-first century. The last speaker of Ubykh, for instance, died in Turkey in 1992 at the age of eighty-eight.

As the fossilized remains of extinct creatures are the rage of affluent collectors so too are artifacts of extinct cultures. So lucrative is the market and so environmentally damaging are the attempts to satisfy demands that laws have had to be passed to ensure that remnants of the extinct themselves do not disappear.

See also: Apocalypse; Darwin, Charles; Disasters; Nuclear Destruction

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MICHAEL C. KEARL

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Extinction

Extinction

Extinction is the irreversible disappearance of all signs of life pertaining to a particular group of organisms. This group can be any of the accepted categories of taxonomic nomenclature, including kingdom, phylum, class, order, family, genus, species, and even subspecies. Most often, extinction is used in reference to the species level organism. The organism may have gone extinct at any time within the past 600 million years of the fossil record or may be in the process of going extinct today. Furthermore, this phenomenon does not pertain only to animals but is also applicable to plants, fungi, protists, bacteria, and archaebacteria.

Many situations can theoretically lead to the extinction of an organism. Determining the cause of extinction is very difficult, especially when information from the fossil record must be used to reconstruct a sequence of events. In many cases, a direct explanation is not forthcoming, and many hypotheses must be examined. Unfortunately, present-day cases of extinction are becoming increasingly common, leading to the need to predict and counteract the disappearance of currently living organisms. Extinction is a natural occurrence well documented in prehuman fossil deposits, and there is evidence that it may allow opportunistic evolution of species that had previously been overshadowed. Human domination of the biosphere, however, is accelerating the extinction rate. For many reasons, human lives are negatively affected by mass extinctions, and humans are struggling to oppose further loss.

Causes of Extinction

Many mechanisms account for extinction. Although organisms depend on other species in their ecosystem for food and population control, this delicate balance may be upset through the pressure of interspecies interactions. If an organism serves as the food source for another, it may be overpredated or overharvested, leading to the death of all members of the taxonomic group. This can occur if the predator/herbivore evolves keener sensory or cognitive capabilities, making it a more efficient consumer. It can also be the result of a food web disruption, such as when an environmental change suddenly favors the propagation of the predator/herbivore without offering such a benefit to the prey. Similarly, when two species occupy the same environmental niche, meaning that they prefer similar habitats and food types, they can be in direct competition for limited resources. If the competing species is better able to inhabit that niche, by gaining more territory and consuming more food, it can drive its competitors to extinction. Humans sometimes hunt animals for sport. This is not exactly predation or competition, but it can also result in the death of an entire species, for example, the dodo bird.

Environmental alteration can also lead to extinction. This may be part of a global climate change, one of Earth's natural climate fluctuations. In this case, one might expect to find a high number of global extinctions, especially among animals in regions greatly affected by the temperature and weather pattern differences. The microenvironment also undergoes change over time. For example, a new mountain range may form along a plain, an island may sink into the ocean, and a river may divert its course. Each of these examples would strongly affect the organisms that depend on those particular microenvironments for sustenance. In some cases, this local regional change can be called habitat loss. This term describes the destruction of a particular type of habitat, such as decline of biodiversity in the North American natural plains, beginning in the nineteenth century.

Evolution can also be considered a direct mode of extinction. Taxonomic boundaries are sometimes very arbitrary, meaning that the distinction between groups is unclear. The lines between groups are drawn using evidence about the organism's habitat, body shape (or morphology), and living habits; most often, however, only the morphology can be relied upon. Some species in the fossil record show gradual change in morphology over evolutionary time. Paleontologists, scientists who research extinct organisms, must sometimes examine a progression from one body type to another and determine at what point the original species can be called a new species. Nonetheless, the original species can no longer exist when the new species begins, and this in itself is a kind of extinction.

Factors that Can Contribute to Extinction

Several factors influence the likelihood that an organism will go extinct. Some species have a very small range, so that they are very susceptible to small-scale changes in the environment. This is an extremely common explanation for the extinction of subspecies. Subspecies sometimes evolve when isolated populations of a species living at the boundaries of its natural range develop distinct behaviors and appearances that distinguish them from the parent species. Given a long enough period of separation from the parent species, these subspecies would develop into an entirely novel organism. Despite this, they often are subject to extinction because their small population size and range cause them to either die out or to be reassimilated into the parent species.

A particular type of feeding pattern is another extinction factor. Whereas generalist feeders, which rely on many sources of nutrition, can switch to a different diet if their food source were to disappear, specialist feeders, which consume only one particular food source, cannot and are therefore highly susceptible to extinction.

Some organisms can be said to have a very delicate niche dynamic for a combination of the above reasons. For example, olive ridley sea turtles return to the same beach year after year to lay eggs. The eggs are highly predated by local animals, and the beaches are often brightly lit and filled with human tourists, factors that decrease the fitness of the mothers and the young. The turtles, however, seem physiologically incapable of choosing other sites for nesting because of their dependence on a particular sort of fine-grained sand and on particular temperature patterns at the chosen beaches.

Once species numbers decline to a small amount of individuals, extinction speed is increased by a factor known as inbreeding depression. This occurs when so few individuals remain in a species that they are forced to mate with members of their own families out of necessity. The smaller gene pool causes increased incidence of genetic disorders, general poor health, and increased susceptibility to disease, all of which increase the species' decline.

Difficulties Determining When an Extinction Has Occurred

Extinctions are not always easy to pinpoint or determine. When a fossil organism stops appearing in the fossil record, this may be explained by a variety of reasons. It may be that environmental conditions during the following period did not favor fossil formation, so that the species survived but was no longer fossilized. Another possibility is that only a small population of a widely dispersed species may live in the region that allows fossilization; if this local population goes extinct, the entire species will disappear from the fossil record, but that does not necessarily mean that the entire species has also gone extinct. Another explanation is that the species may have merely migrated from a fossil-friendly environment to a fossil-unfriendly habitat, or perhaps to a region for which the fossil bed has not yet been found. A confounding factor in determining extinction can be as simple as researcher bias. Organisms seem to go extinct at the boundaries between geological periods of Earth's history, but this may be due to a quirk of the field of paleontology: Paleontologists often study only one period in the rock strata. They categorize all organisms that appear at the beginning of their period, and may not realize that the scientists researching an earlier period have already named the same species. Thus although it appears that an organism has become extinct, in reality it has just been mistakenly renamed.

Paleontologists try to account for all of these sources of error through thorough study and the use of probability equations, but the fossil record is irregular and difficult to interpret. For example, in the mid-twentieth century, the coelacanth, a species of bony fish that scientists had falsely declared extinct, was rediscovered as a living species. Coelacanths were thought to have gone extinct 70 million years ago because they disappeared from the fossil record. This mistake was remedied in 1938 when a fisherman caught a living coelacanth off the coast of southeastern Africa.

Reasons for Preventing Extinctions

Although extinction is a natural occurrence, there are many reasons to actively protect existing species from extinction. More and more, ecosystems are viewed as integrated modules, so that the extinction of one species in the ecosystem can disrupt all of the other species' population dynamics. If humans ignore the extinction of a seemingly uninteresting species, this could cause widespread extinctions in many other organisms. In general, biodiversity (the presence of a high number of species in an environment) is equated with a healthy ecosystem, and high extinction rates decrease biodiversity. Often, an environment of low biodiversity reveals what humans consider to be pests. These are merely organisms that are able to survive in an ecosystem reduced and dominated by humans. People naturally prefer a healthier ecosystem, with clean breathing air, green surroundings, and a wide variety of species. There is a value to the beauty of the environment, which is damaged by high extinctions. Furthermore, humans directly depend on some species for medical benefits, such as medicine, tissue and organ donations, and animal models of human disease. Organisms that go extinct can no longer be researched as possible cures for human ailments or be studied by engineers as models for building computers, machinery, and vehicles.

Preventing extinction is a political as well as a biological priority. The needs of humans often overshadow the decline of endangered species. For example, the economy of many Third World countries depends on agriculture. If natural ecosystems such as rain forests must be destroyed to support the agricultural needs of these nations, many species are put at risk and forced into extinction. Without that source of income, however, the peoples of these countries could languish and starve. A balance between preserving the rain forest habitat and ensuring the well-being of the humans must be sought.

Methods of Preventing Extinction

There are several contemporary means of preserving a particular species. Active breeding programs at nature reserves and at zoos attempt to maintain a sizable population of individuals to avoid inbreeding depression. When animals such as cheetahs are the victims of inbreeding depression, specialized veterinarians and behaviorists monitor their health and attempt to circumvent the danger of disease. Hunting and fishing regulations attempt to predict population flux and disallow overharvesting of game animals. Specialized herbariums and eco-landscaping firms are working to restore lost habitats within depleted landscapes.

Despite these endeavors, there is still an acute danger that many of the world's habitats will be thrown into disarray by human intervention. The shrinkage and parceling of natural habitats is especially damaging to animals with large ranges, such as Siberian tigers, bald eagles, and buffalo. Nature preserves are under constant study to improve the efficiency of the surroundings in order to prevent extinction. span>

see also Feeding Strategies; Fossil Record; Habitat Loss; Habitat Restoration; Hunting; Paleontology; Zoological Parks.

Rebecca M. Steinberg

Bibliography

Courtillot, Vincent. Evolutionary Catastrophes: The Science of Mass Extinction. Cambridge, U.K.: Cambridge University Press, 1999.

Glen, William, ed. The Mass-Extinction Debates: How Science Works in a Crisis. Stanford, CA: Stanford University Press, 1994.

Hallam, Anthony, and Paul B. Wignall. Mass Extinctions and Their Aftermath. Oxford,

U.K.: Oxford University Press, 1997.

Raup, David M. Extinction: Bad Genes or Bad Luck? New York: Norton, 1992.

Schneiderman, Jill S. The Earth Around Us: Maintaining a Livable Planet. New York:

W. H. Freeman, 2000.

Snyder, Noel F., and Helen Snyder. The California Condor: A Saga of Natural History and Conservation. San Diego: Academic Press, 2000.

Weinberg, Samantha. A Fish Caught in Time: The Search for the Coelacanth. New York:

Harper Collins, 2000.

CALIFORNIA CONDOR

California condors are the largest birds in North America, weighing up to 11.5 kilograms (25 pounds), with a wingspan of more than 2.7 meters (9 feet). In 1967 condors had declined to approximately thirty individuals. In 2000, eighty-seven condors were living, but only three were in the wild. While captive breeding programs have improved the outlook for condors, their future now depends entirely on human intervention.

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Extinction

Extinction

Extinction is the termination of evolutionary lineage . The most common extinction event is the loss of a species. There are many reasons why a species might die out. Human intervention (either directly or indirectly) has become the leading cause of species extinction (possibly for the last fifteen thousand years).

Species and Populations

An important distinction must be made between true extinction and extirpation. Extirpation is the loss of a population, or loss of a species from a particular geographic region. A famous twentieth-century example is the extirpation of wolves from the Yellowstone region of Wyoming. The park service reintroduced wolves to Yellowstone in the 1990s, and these predators appear to be adapting well to their new home. True extinction must also be differentiated from pseudoextinction. Biologists studying the changes that take place in a lineage over time often designate distinct morphological stages as separate species. The extinction of a species in this context is not the result of the termination of a lineage, but rather the transformation into a new form.


The giant panda actually has a carnivorous digestive system, so it must eat voraciously for 10 to 12 hours to consume enough bamboo (up to 66 pounds [30 kilograms]) each day.


A clear understanding of the definition of a species is necessary in order to discuss extinction. This is not a simple question, but one view defines a species as a population of potentially interbreeding individuals that is reproductively isolated from other such populations. By this definition the relatively common mating between coyotes and domestic dogs raises the question of the validity of their separate species status.

Environmental Change

Species go extinct primarily because they are unable to adapt to a changing environment. Animals with specialized food or habitat requirements, such as the giant panda (which feeds almost exclusively on bamboo), are particularly susceptible to environmental changes. Generalist species that feed on many types of food and live in a variety of settings are much more able to survive in a changing environment. For example, raccoons are common city dwellers, where they forage from trash cans instead of from streams. In addition, species with long generation times that produce few offspring are often vulnerable to extinction. If a population of animals is very small, it is subject to extinction from a variety of factors, such as disturbances and diseases. Organisms with short generation times that produce a lot of offspring, for example, many rodents and insect species, are often capable of increasing their populations quickly and therefore become less vulnerable to extinction. However, animals such as the rhinoceros or Siberian tiger take several years to mature and when they do reproduce only give birth to one or two offspring. Thus, species such as these cannot rebound from low populations quickly and thus are more likely to go extinct.

A firm grasp of ecological principles is crucial to an understanding of how species interactions can lead to extinction. Two species with significantly overlapping niches are unlikely to coexist over time unless some mechanism prevents either species from reaching its carrying capacity (the maximum number of individuals the habitat can sustain). Typically the species that is better adapted will drive the other species to extinction. This phenomenon is particularly important because of the widespread introduction of exotic species by humans. Many studies have shown the impact of domestic cats and dogs on native prey species. Less obvious, however, is their competitive impact on native predators.

The extinction of the Tasmanian wolf in the twentieth century is probably the best-known example of this negative impact on biodiversity. Typically whenever there is considerable overlap between the niches of a placental and a marsupial the placental will win out. The reasons for placental superiority are not entirely clear (relatively greater intelligence and reproductive physiology are possibilities), but this fact probably accounts for the existence of only one successful species of marsupial in North America, the opossum, a broad generalist with a very high reproductive rate.

Mass Extinctions

Mass extinction events have occurred periodically in Earth's history. Three of these events are particularly relevant to mammalian history. The first was the Cretaceous-Tertiary extinction 65 million years ago that led to the demise of the dinosaurs. Mammals and dinosaurs coexisted for approximately 140 million years, during which time dinosaurs dominated the majority of large terrestrial vertebrate niches. This extinction most likely was the result of a large meteor impact that eliminated over half of all species on the planet. Mammals survived that extinction event relatively well, probably because the majority of Mesozoic mammals were species with short generation times and large litters. During the Tertiary period, mammals underwent a rapid adaptive radiation , filling niches similar to those vacated by dinosaurs.

A second major extinction event occurred during the Eocene-Oligocene period, 30 to 35 million years ago. This extinction was the result of global cooling due to changes in ocean current patterns. Prior to this period modern families of mammals comprised only about 15 percent of the mammalian fauna; after cooling modern mammals made up more than 50 percent of the fauna at the family level.

The third mass extinction event began around 15,000 years ago and is still ongoing. Large species (mammoths, ground sloths, horses, camels, and lions) were more adversely impacted by the most recent extinction event than other taxa. In the twenty-first century, there are only about a dozen species of large mammals (over 100 pounds) in North America. As recently as 11,000 years ago there may have been three times that number.

There is controversy about what caused the extinction of these large mammals. Three possibilities include global warming at the end of the last major glaciation, overkill by early North American humans, and contagious diseases. The timing of each of these events correlates with the time of extinction, therefore determining which hypothesis is most likely must be based on the merits of each argument. Reduction in size of suitable habitat is the most likely factor if the extinction is due to climatic change. Much of North America was covered by a grassland habitat during the last glacial period. As this habitat declined the largest species may have been unable to adapt to the new conditions. Migration of humans into North America is the causative agent for the other two hypotheses. According to these models, the megafauna went extinct either directly through predation by a highly efficient hunter or indirectly by the introduction of exotic, infectious organisms.

In the late twentieth and early twenty-first centuries, large-scale habitat destruction in tropical forests and elsewhere has caused extinction of significant numbers of species, many not fully identified. Pressures from population increase, agricultural expansion, and forest cleaning threaten many thousands of species throughout the world.

see also Biodiversity; Conservation; Endangered Species; Evolution; Forest, Tropical; Population Dynamics; Species

William P. Wall

Bibliography

Courtillot, V. Evolutionary Catastrophes: The Science of Mass Extinction. New York: Cambridge University Press, 1999.

Lewin, R. The Sixth Extinction: Patterns of Life and the Future of Humankind. New York: Anchor Books, 1996.

Pianka, Eric. R. Evolutionary Ecology. San Francisco, CA: Benjamin Cummings, 2000.

Raup, David. Extinction: Bad Genes or Bad Luck. New York: W. W. Norton & Company, 1992.

Vaughan, Terry A., James M. Ryan, and Nicholas J. Czaplewski. Mammalogy. Fort Worth, TX: Saunders College Publishing, 2000.

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Extinction

Extinction

The elimination of a conditioned response by withholding reinforcement.

In classical/respondent conditioning , the learned response disappears when the association between conditioned and unconditioned stimuli is eliminated. For example, when a conditioned stimulus (a light) is presented with an unconditioned stimulus (meat), a dog may be trained to salivate in response to the conditioned stimulus. If the unconditioned stimulus does not appear at least some of the time, however, its association with the conditioned stimulus will be lost, and extinction of the dog's learned or conditioned response will occur. As a result, the dog will stop salivating in response to the light.

In operant conditioning , the experimental subject acquires a conditioned response by learning that its actions will bring about specific consequences, either positive or negative. When the link between this operant response and its consequences is not reinforced, extinction of the response occurs. Thus, a rat that has learned that pressing a lever in its cage will produce a food pellet will gradually stop pressing the lever if the food pellets fail to appear.

Just as behavioral therapies use reinforcement to foster desirable behaviors, they may achieve the extinction of undesirable ones by removing various forms of reinforcement. For example, rowdy or otherwise inappropriate behavior by children is often "rewarded" by attention from both adults and peers. Sending a child to "time out" short circuits this process and can eliminate the undesirable behavior by removing the reward. Although it works slowly, extinction is a popular technique for modifying behavior in children.

Further Reading

Craighead, W. Edward. Behavior Modification: Principles, Issues, and Applications. Boston: Houghton Mifflin, 1976.

Skinner, B.F. About Behaviorism. New York: Knopf, 1974.

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Extinction

237. Extinction

  1. bald eagle once on verge of extinction, this bird is now protected; still an endangered species. [Ecology: Hammond, 290]
  2. dinosaur dinosaurs died out, unable to adapt to environmental change. [Ecology: Hammond, 290]
  3. dodo large, flightless bird exterminated on Mauritius. [Ecology: Wallechinsky, 131]
  4. great auk hunters killed such large numbers, these birds became extinct in 1840s. [Ecology: Hammond, 290]
  5. heath hen human settlement of U.S. Atlantic Coast contributed to the extinction of these birds. [Ecology: Hammond, 290]
  6. Last of the Mohicans, The novel foreseeing the extinction of various Indian tribes. [Am. Lit.: The Last of the Mohicans ]
  7. mastodon similar to the elephant, the mastodon is now extinct. [Ecology: Hammond, 290]
  8. moa large ostrichlike bird, hunted chiefly for its food; it died out in 1914. [Ecology: Hammond, 290]
  9. passenger pigeon hunted to extinction by 1914; vast numbers once darkened American skies during migratory flights. [Ecology: EB, VII: 786]
  10. saber-toothed tiger wild cat that died out about 12,000 years ago. [Ecology: Hammond, 290]
  11. Last of the Barons, The portrays Englands brilliant aristocracy as dying breed (1470s). [Br. Lit.: The Last of the Barons, Magill I, 492494]
  12. whale many species in danger of extinction, owing to massive hunting. [Ecology: Hammond, 290]

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extinction

extinction
1. In optical mineralogy, a mineral is said to be in extinction when the vibration direction of the two rays of a doubly refracting crystal coincide with the vibration directions of the two pieces of Polaroid in a thin-section microscope that is parallel to the polarizer and analyser so that no light reaches the eye. This phenomenon occurs four times in a complete 360° rotation of the stage. See OBLIQUE EXTINCTION; STRAIGHT EXTINCTION; SYMMETRICAL EXTINCTION; and UNDULOSE EXTINCTION.

2. The elimination of a taxon. This may take place in several ways. In the simplest case the taxon disappears from the record and is not replaced. Alternatively, one taxon may replace another, the earlier group consequently disappearing. Thus there is a process of either subtraction or substitution. Extinction generally takes place at particular times and places but there are recurring periods when episodes of mass extinction have taken place. Environmental catastrophe, occurring for whatever reason, removes many groups from the environment and ecosystems collapse. Eventually new forms appear and evolution resumes. It would appear that periods of mass extinction control the pattern of evolution.

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extinction

extinction, in biology, disappearance of species of living organisms. Extinction usually occurs as a result of changed conditions to which the species is not suited. If no member of the affected species survives and reproduces, the entire line dies out, leaving no descendants. This was the case with the saber-toothed cat (Smilodon) of North America, which is not ancestral to any living species. However, a species may also become extinct through its gradual evolution into a new species, as a result of natural selection for characteristics suited for new conditions. An example of the latter situation is the evolution of horses from the eophippus (Hyracotherium) to Miohippus to Merychippus to the present-day Equus. There has been an unbroken line of descent, yet horses of the earlier types no longer exist. Human activities, such as overhunting a species or destroying its habitat, have caused the extinction of some species, such as the passenger pigeon and dodo, and threatened many others (see endangered species). See also mass extinction.

See M. V. Barrow, Jr., Nature's Ghosts: Confronting Extinction from the Age of Jefferson to the Age of Ecology (2009); E. Fuller, Lost Animals: Extinction and the Photographic Record (2014).

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extinction

extinction
1. The irreversible condition of a species or other group of organisms of having no living representatives in the wild, which follows the death of the last surviving individual of that species or group. Extinction may occur on a local or global level; it can result from various human activities, including the destruction of habitats or the overexploitation of species that are hunted or harvested as a resource. Species at the top of a food chain (e.g. large birds of prey) will be more prone to extinction since they exist in relatively small numbers and will be affected by a deleterious change at any of the levels in the food chain. See mass extinction.

2. The termination of a behaviour pattern that is no longer appropriate. For example, dogs can be conditioned to salivate when they hear a bell ring in the absence of a food stimulus (see conditioning). However, if the bell continues to be rung in the absence of food the dogs will gradually stop salivating on hearing the bell.

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extinction

extinction
1. The elimination of a taxon. This may take place in several ways. In the simplest case the taxon disappears from the record and is not replaced. Alternatively, one taxon may replace another, the earlier group consequently disappearing. Thus there is a process of either subtraction or substitution. Extinction generally takes place at particular times and places, but there are recurring periods when episodes of mass extinction have taken place. Environmental catastrophe, occurring for whatever reason, removes many groups from the environment and ecosystems collapse. Eventually new forms appear and evolution resumes. It would appear that periods of mass extinction control the pattern of evolution.

2. The loss of learned patterns of behaviour from the repertoire of an animal to which they have become irrelevant.

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extinction

ex·tinc·tion / ikˈsting(k)shən/ • n. 1. the state or process of being or becoming extinct: the extinction of the great auk. ∎  the state or process of ceasing or causing something to cease to exist: the extinction of liberalism. ∎  the wiping out of a debt. 2. Physics reduction in the intensity of light or other radiation as it passes through a medium or object, due to absorption, reflection, and scattering: ultraviolet extinction.

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extinction

extinction Dying out of a species or population. Extinction is part of the process of evolution in which certain species of plants and animals die out, often to be replaced by others. Natural disasters may also lead to extinctions; a giant meteor impact may have caused the disappearance of dinasaurs. Extinctions brought about by human impact on the environment do not necessarily involve the replacement of extinct species by others.

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extinction

extinction
1. The elimination of a taxon.

2. The loss of learned patterns of behaviour from the repertoire of an animal to which they have become irrelevant.

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extinction

extinction (iks-tink-shŏn) n. (in psychology) the weakening of a conditioned reflex that takes place if it is not maintained by reinforcement.

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extinction

extinction The elimination of a taxon.

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"extinction." A Dictionary of Plant Sciences. . Encyclopedia.com. (July 25, 2017). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/extinction-1

"extinction." A Dictionary of Plant Sciences. . Retrieved July 25, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/extinction-1

Extinction

Extinction

See Evolution

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"Extinction." Encyclopedia of Science and Religion. . Encyclopedia.com. 25 Jul. 2017 <http://www.encyclopedia.com>.

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"Extinction." Encyclopedia of Science and Religion. . Retrieved July 25, 2017 from Encyclopedia.com: http://www.encyclopedia.com/education/encyclopedias-almanacs-transcripts-and-maps/extinction

extinction

extinctionashen, fashion, passion, ration •abstraction, action, attraction, benefaction, compaction, contraction, counteraction, diffraction, enaction, exaction, extraction, faction, fraction, interaction, liquefaction, malefaction, petrifaction, proaction, protraction, putrefaction, redaction, retroaction, satisfaction, stupefaction, subtraction, traction, transaction, tumefaction, vitrifaction •expansion, mansion, scansion, stanchion •sanction •caption, contraption •harshen, Martian •cession, discretion, freshen, session •abjection, affection, circumspection, collection, complexion, confection, connection, convection, correction, defection, deflection, dejection, detection, direction, ejection, election, erection, genuflection, imperfection, infection, inflection, injection, inspection, insurrection, interconnection, interjection, intersection, introspection, lection, misdirection, objection, perfection, predilection, projection, protection, refection, reflection, rejection, resurrection, retrospection, section, selection, subjection, transection, vivisection •exemption, pre-emption, redemption •abstention, apprehension, ascension, attention, circumvention, comprehension, condescension, contention, contravention, convention, declension, detention, dimension, dissension, extension, gentian, hypertension, hypotension, intention, intervention, invention, mention, misapprehension, obtention, pension, prehension, prevention, recension, retention, subvention, supervention, suspension, tension •conception, contraception, deception, exception, inception, interception, misconception, perception, reception •Übermenschen • subsection •ablation, aeration, agnation, Alsatian, Amerasian, Asian, aviation, cetacean, citation, conation, creation, Croatian, crustacean, curation, Dalmatian, delation, dilation, donation, duration, elation, fixation, Galatian, gyration, Haitian, halation, Horatian, ideation, illation, lavation, legation, libation, location, lunation, mutation, natation, nation, negation, notation, nutation, oblation, oration, ovation, potation, relation, rogation, rotation, Sarmatian, sedation, Serbo-Croatian, station, taxation, Thracian, vacation, vexation, vocation, zonation •accretion, Capetian, completion, concretion, deletion, depletion, Diocletian, excretion, Grecian, Helvetian, repletion, Rhodesian, secretion, suppletion, Tahitian, venetian •academician, addition, aesthetician (US esthetician), ambition, audition, beautician, clinician, coition, cosmetician, diagnostician, dialectician, dietitian, Domitian, edition, electrician, emission, fission, fruition, Hermitian, ignition, linguistician, logician, magician, mathematician, Mauritian, mechanician, metaphysician, mission, monition, mortician, munition, musician, obstetrician, omission, optician, paediatrician (US pediatrician), patrician, petition, Phoenician, physician, politician, position, rhetorician, sedition, statistician, suspicion, tactician, technician, theoretician, Titian, tuition, volition •addiction, affliction, benediction, constriction, conviction, crucifixion, depiction, dereliction, diction, eviction, fiction, friction, infliction, interdiction, jurisdiction, malediction, restriction, transfixion, valediction •distinction, extinction, intinction •ascription, circumscription, conscription, decryption, description, Egyptian, encryption, inscription, misdescription, prescription, subscription, superscription, transcription •proscription •concoction, decoction •adoption, option •abortion, apportion, caution, contortion, distortion, extortion, portion, proportion, retortion, torsion •auction •absorption, sorption •commotion, devotion, emotion, groschen, Laotian, locomotion, lotion, motion, notion, Nova Scotian, ocean, potion, promotion •ablution, absolution, allocution, attribution, circumlocution, circumvolution, Confucian, constitution, contribution, convolution, counter-revolution, destitution, dilution, diminution, distribution, electrocution, elocution, evolution, execution, institution, interlocution, irresolution, Lilliputian, locution, perlocution, persecution, pollution, prosecution, prostitution, restitution, retribution, Rosicrucian, solution, substitution, volution •cushion • resumption • München •pincushion •Belorussian, Prussian, Russian •abduction, conduction, construction, deduction, destruction, eduction, effluxion, induction, instruction, introduction, misconstruction, obstruction, production, reduction, ruction, seduction, suction, underproduction •avulsion, compulsion, convulsion, emulsion, expulsion, impulsion, propulsion, repulsion, revulsion •assumption, consumption, gumption, presumption •luncheon, scuncheon, truncheon •compunction, conjunction, dysfunction, expunction, function, junction, malfunction, multifunction, unction •abruption, corruption, disruption, eruption, interruption •T-junction • liposuction •animadversion, aspersion, assertion, aversion, Cistercian, coercion, conversion, desertion, disconcertion, dispersion, diversion, emersion, excursion, exertion, extroversion, immersion, incursion, insertion, interspersion, introversion, Persian, perversion, submersion, subversion, tertian, version •excerption

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"extinction." Oxford Dictionary of Rhymes. . Encyclopedia.com. 25 Jul. 2017 <http://www.encyclopedia.com>.

"extinction." Oxford Dictionary of Rhymes. . Encyclopedia.com. (July 25, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/extinction

"extinction." Oxford Dictionary of Rhymes. . Retrieved July 25, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/extinction