Review Extinct Species: Past, Present & Future...

Discussion in 'Science & Technology' started by Doctor Omega, Mar 20, 2018.

  1. Doctor Omega

    Doctor Omega Moderator

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

    More than 99 percent of all species, amounting to over five billion species,[1] that ever lived on Earth are estimated to be extinct.[2][3][4]Estimates on the number of Earth's current species range from 10 million to 14 million,[5] of which about 1.2 million have been documented and over 86 percent have not yet been described.[6] More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described.[7]

    Through evolution, species arise through the process of speciation—where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche—and species become extinct when they are no longer able to survive in changing conditions or against superior competition. The relationship between animals and their ecological niches has been firmly established.[8] A typical species becomes extinct within 10 million years of its first appearance,[4] although some species, called living fossils, survive with virtually no morphological change for hundreds of millions of years.

    Mass extinctions are relatively rare events; however, isolated extinctions are quite common. Only recently have extinctions been recorded and scientists have become alarmed at the current high rate of extinctions.[9][10][11][12] 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.[13]

    A dagger symbol (†) placed next to the name of a species or other taxon is often done to indicate its status as extinct.



     
  2. Doctor Omega

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    Last male northern white rhino dies




     
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    Causes

    As long as species have been evolving, species have been going extinct. It is estimated that over 99.9% of all species that ever lived are extinct. The average lifespan of a species is 1–10 million years,[23] although this varies widely between taxa. There are a variety of causes that can contribute directly or indirectly to the extinction of a species or group of species. "Just as each species is unique", write Beverly and Stephen C. Stearns, "so is each extinction ... the causes for each are varied—some subtle and complex, others obvious and simple".[24] Most simply, any species that cannot survive and reproduce in its environment and cannot move to a new environment where it can do so, dies out and becomes extinct. Extinction of a species may come suddenly when an otherwise healthy species is wiped out completely, as when toxic pollution renders its entire habitat unliveable; or may occur gradually over thousands or millions of years, such as when a species gradually loses out in competition for food to better adapted competitors. Extinction may occur a long time after the events that set it in motion, a phenomenon known as extinction debt.

    Assessing the relative importance of genetic factors compared to environmental ones as the causes of extinction has been compared to the debate on nature and nurture.[25] The question of whether more extinctions in the fossil record have been caused by evolution or by catastrophe is a subject of discussion; Mark Newman, the author of Modeling Extinction, argues for a mathematical model that falls between the two positions.[4] By contrast, conservation biology uses the extinction vortex model to classify extinctions by cause. When concerns about human extinction have been raised, for example in Sir Martin Rees' 2003 book Our Final Hour, those concerns lie with the effects of climate change or technological disaster.

    Currently, environmental groups and some governments are concerned with the extinction of species caused by humanity, and they try to prevent further extinctions through a variety of conservation programs.[9] Humans can cause extinction of a species through overharvesting, pollution, habitat destruction, introduction of invasive species (such as new predators and food competitors), overhunting, and other influences. Explosive, unsustainable human population growth is an essential cause of the extinction crisis.[26] According to the International Union for Conservation of Nature (IUCN), 784 extinctions have been recorded since the year 1500, the arbitrary date selected to define "recent" extinctions, up to the year 2004; with many more likely to have gone unnoticed. Several species have also been listed as extinct since 2004.
     
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    Modern extinctions


    Further information: Deforestation and Defaunation
    According to a 1998 survey of 400 biologists conducted by New York's American Museum of Natural History, nearly 70% believed that the Earth is currently in the early stages of a human-caused mass extinction,[48] known as the Holocene extinction. In that survey, the same proportion of respondents agreed with the prediction that up to 20% of all living populations could become extinct within 30 years (by 2028). A 2014 special edition of Science declared there is widespread consensus on the issue of human-driven mass species extinctions.[49]

    Biologist E. O. Wilson estimated [13] in 2002 that if current rates of human destruction of the biosphere continue, one-half of all plant and animal species of life on earth will be extinct in 100 years.[50] More significantly, the current rate of global species extinctions is estimated as 100 to 1000 times "background" rates (the average extinction rates in the evolutionarytime scale of planet Earth),[51][52] while future rates are likely 10,000 times higher.[52] However, some groups are going extinct much faster. Biologists Paul R. Ehrlich and Stuart Pimm, among others, contend that human population growth and overconsumption are the main drivers of the modern extinction crisis.[
     
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    Proposed

    The poliovirus is now confined to small parts of the world due to extermination efforts.[81]

    Dracunculus medinensis, a parasitic worm which causes the disease dracunculiasis, is now close to eradication thanks to efforts led by the Carter Center.[82]

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

    Biologist Olivia Judson has advocated the deliberate extinction of certain disease-carrying mosquito species. In a September 25, 2003 New York Times article, she advocated "specicide" of thirty mosquito species by introducing a genetic element which can insert itself into another crucial gene, to create recessive "knockout genes".[83] She says that the Anopheles mosquitoes (which spread malaria) and Aedes mosquitoes (which spread dengue fever, yellow fever, elephantiasis, and other diseases) represent only 30 species; eradicating these would save at least one million human lives per annum, at a cost of reducing the genetic diversity of the family Culicidae by only 1%. She further argues that since species become extinct "all the time" the disappearance of a few more will not destroy the ecosystem: "We're not left with a wasteland every time a species vanishes. Removing one species sometimes causes shifts in the populations of other species—but different need not mean worse." In addition, anti-malarial and mosquito control programs offer little realistic hope to the 300 million people in developing nations who will be infected with acute illnesses this year. Although trials are ongoing, she writes that if they fail: "We should consider the ultimate swatting."[83]

    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."
     
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    Cloning

    Some, such as Harvard geneticist George M. Church, believe that ongoing technological advances will let us "bring back to life" an extinct species by cloning, using DNA from the remains of that species. Proposed targets for cloning include the mammoth, the thylacine, and the Pyrenean ibex. For this to succeed, enough individuals would have to be cloned, from the DNA of different individuals (in the case of sexually reproducing organisms) to create a viable population. Though bioethical and philosophical objections have been raised,[85] the cloning of extinct creatures seems theoretically possible.[86]

    In 2003, scientists tried to clone the extinct Pyrenean ibex (C. p. pyrenaica). This attempt failed: of the 285 embryos reconstructed, 54 were transferred to 12 mountain goats and mountain goat-domestic goat hybrids, but only two survived the initial two months of gestation before they too died.[87] In 2009, a second attempt was made to clone the Pyrenean ibex: one clone was born alive, but died seven minutes later, due to physical defects in the lungs.
     
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    Stephen Hawking:Human species will not last for another 1,000 years




     
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    Wildlife Expert Catches 'Extinct' Zanzibar Leopard on Camera



     

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