Extinction
The thylacine, also known as the Tasmanian tiger, died in Hobart Zoo in Tasmania on the 7th of September 1936. This single death marked the end of a species that had once roamed the Australian landscape. Scientists define extinction as the moment when the last existing member of a taxon dies and can no longer reproduce. A species may become functionally extinct before this final moment if it loses the capacity to recover its population. Determining exactly when this happens is difficult because potential ranges for many species are vast. This difficulty leads to phenomena such as Lazarus taxa. A Lazarus taxon refers to instances where a species or taxon was thought to be extinct but was later rediscovered. The coelacanth serves as a famous example. This fish related to lungfish and tetrapods was considered extinct since the end of the Cretaceous Period until 1938. In that year, a living specimen was found off the Chalumna River on the east coast of South Africa. Another recent case involves Attenborough's long-beaked echidna from Papua New Guinea. It had not been sighted since 1962 and was believed possibly extinct until recorded again in November 2023.
Over 99.9% of all species that ever lived are now extinct according to estimates. The average lifespan of a species ranges between one million and ten million years. Extinction occurs when a species cannot survive and reproduce in its environment. It may happen suddenly when toxic pollution renders an entire habitat unliveable. Alternatively, extinction can occur gradually over thousands or millions of years through competition for food. Smaller populations face higher risks because they have fewer beneficial mutations entering each generation. Limited geographic range is the most important determinant of genus extinction at background rates. Small population size makes it easier for slightly deleterious mutations to fix within the group. This creates a positive feedback loop known as mutational meltdown. Genetic diversity plays a critical role in survival. A diverse gene pool gives a population a higher chance of surviving adverse changes. Population bottlenecks reduce genetic diversity by limiting the number of reproducing individuals. Inbreeding becomes more frequent during these bottlenecks. Habitat degradation alters the fitness landscape so severely that a species can no longer persist. Toxicity can kill off members rapidly or sterilize them over time. Diminished resources often accompany habitat loss leading to further decline. Competition from new predator species also threatens native populations.
A 2019 Global Assessment Report on Biodiversity and Ecosystem Services revealed alarming statistics about current biodiversity loss. The biomass of wild mammals has fallen by 82% since human expansion began. Natural ecosystems have lost approximately half their area globally. One million plant and animal species are now at risk of extinction due largely to human actions. Twenty-five percent of all plant and animal species face threats of disappearance. The main driver remains the destruction of natural habitats through activities like cutting down forests. Converting land into fields for farming eliminates dense vegetation needed by many species. Slash-and-burn agriculture techniques used in tropical developing countries place enormous pressure on forests. Overharvesting, pollution, introduction of invasive species, and unsustainable consumption patterns accelerate the crisis. A 2014 special edition of Science declared there is widespread consensus on human-driven mass extinctions. Biologist E.O. Wilson estimated in 2002 that one-half of all plant and animal species could be extinct within 100 years if current rates continue. Current global extinction rates are estimated as 100 to 1,000 times higher than background levels. Future projections suggest these rates may become 10,000 times higher still. In January 2020, the UN's Convention on Biological Diversity drafted a plan establishing a deadline of 2030 to protect 30% of Earth's land and oceans.
Prior to the 19th century, Western society adhered to the belief that the world was created complete and perfect. Thomas Jefferson famously denied the extinction of the woolly mammoth because nature never allows a race of animals to disappear. In October 1686, Robert Hooke presented an impression of a nautilus shell more than two feet in diameter to the Royal Society. He theorized it lived in deep oceans rather than being truly gone. Sir Thomas Molyneux published an account of enormous antlers found in Ireland in 1695. He reasoned they belonged to moose once common on British Isles instead of indicating total loss. Georges Cuvier established modern conceptions of catastrophic extinction through a lecture delivered to the French Institute in 1796. His primary evidence came from mammoth skulls discovered near Paris which were distinct from any known living elephant species. In 1804, he named the extinct mammal genus Palaeotherium based on skull material from the Paris Basin. Jean-Baptiste Lamarck argued for gradual change over time while Cuvier proposed periodic catastrophic flooding events wiped out huge numbers of species. Charles Lyell later demonstrated that saltwater and freshwater deposits could form by slow sea level changes rather than sudden floods. It was not until 1982 when David Raup and Jack Sepkoski published their seminal paper on mass extinctions that Cuvier's views gained acceptance. The current understanding synthesizes both cataclysmic events and background extinction processes.
The International Union for Conservation of Nature maintains a conservation status called "extinct in the wild" (EW). Species listed under this category are not known to have any living specimens outside artificial environments like zoos. Some of these species are functionally extinct as they no longer exist within natural habitats. Modern zoological institutions attempt to maintain viable populations through carefully planned breeding programs. The smallpox virus is now extinct in the wild though samples remain in laboratory settings. Dracunculus medinensis or Guinea worm is close to eradication thanks to efforts led by the Carter Center. Biologist Olivia Judson advocated specicide of thirty mosquito species in an article published the 25th of September 2003. She suggested introducing genetic elements to create recessive knockout genes in Anopheles mosquitoes spreading malaria. Eradicating these would save at least one million human lives annually while reducing family Culicidae diversity by only 1%. Biologist E.O. Wilson also supported removing several disease-carrying mosquito species including Anopheles gambiae. Campaigns successfully locally eradicated tsetse flies across parts of Africa including Príncipe island. Harvard geneticist George M. Church believes ongoing technological advances will allow bringing back extinct species via cloning. In 2009 scientists tried cloning the Pyrenean ibex but the clone died seven minutes later due to lung defects.
Common questions
When did the thylacine die in Hobart Zoo?
The thylacine died on the 7th of September 1936. This death marked the end of a species that had once roamed the Australian landscape.
What is an example of a Lazarus taxon rediscovered after being thought extinct?
The coelacanth serves as a famous example of a Lazarus taxon. This fish was considered extinct since the end of the Cretaceous Period until 1938 when a living specimen was found off the Chalumna River on the east coast of South Africa.
How many plant and animal species are at risk of extinction due to human actions?
One million plant and animal species are now at risk of extinction due largely to human actions. Twenty-five percent of all plant and animal species face threats of disappearance according to a 2019 Global Assessment Report on Biodiversity and Ecosystem Services.
Who established modern conceptions of catastrophic extinction through a lecture in 1796?
Georges Cuvier established modern conceptions of catastrophic extinction through a lecture delivered to the French Institute in 1796. His primary evidence came from mammoth skulls discovered near Paris which were distinct from any known living elephant species.
When did scientists try cloning the Pyrenean ibex and what happened to the clone?
Scientists tried cloning the Pyrenean ibex in 2009 but the clone died seven minutes later due to lung defects. The International Union for Conservation Nature maintains a conservation status called extinct in the wild for species not known to have any living specimens outside artificial environments like zoos.