Holocene extinction
The Holocene extinction, also known as the Anthropocene extinction or the sixth mass extinction, refers to the ongoing loss of species primarily driven by human activities during the Holocene epoch, which began around 12,000 years ago. This period marks significant changes in human civilization, particularly following the advent of agriculture about 10,000 years ago, which allowed for larger populations and intensified land use. Scientists estimate that human actions threaten up to one million plant and animal species through activities such as deforestation, hunting, overfishing, and pollution, leading to an unprecedented rate of extinction. The natural extinction rate is typically one to five species per year; however, estimates suggest that dozens of species may be going extinct daily in the early 21st century. Habitat destruction is identified as the primary cause of this crisis, with vast areas of natural environments being converted for agriculture and urban development. The loss of biodiversity, which refers to the variety of life forms within a given ecosystem, is crucial for species survival, as it enables resilience against threats like disease and climate change. The decline in genetic diversity within species, such as the platypus, further exacerbates their vulnerability. Overall, the Holocene extinction highlights the critical intersection of human activity and ecological balance, raising urgent concerns about the future of global biodiversity.
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Subject Terms
Holocene extinction
The Holocene extinction refers to the loss of species due to human activity during the Holocene epoch. It is also sometimes referred to as the Anthropocene extinction or the sixth mass extinction. The Holocene epoch began about 12,000 years ago at the end of the last ice age and continues into modern times. The development of agriculture, which began about 10,000 years ago, greatly changed human civilization and the planet, allowing larger populations of humans to affect ever-increasing areas of land.
A mass extinction is defined as a period when at least 60 percent of extant genera become extinct within a few hundred thousand years. Extant refers to those living, while genera is the plural form of genus, the taxonomic rank of biological classification that is below family and above species. For example, the genus Homo includes modern humans (Homo sapiens) and their extinct close relatives, such as Homo neanderthalensis and Homo floresiensis. While not all scientists agree, many believe a sixth mass extinction event is taking place in modern times.
Background
The last mass extinction occurred at the end of the Cretaceous Period, 65 million years ago. Scientists believe a large asteroid that struck the planet caused the fifth mass extinction, which resulted in the extinction of all non-avian dinosaurs and the eventual rise of mammals. The asteroid impact killed off about 76 percent of all species on the planet. Earlier mass extinctions have been caused by events such as enormous volcanic eruptions or global cooling.
When the last ice age ended about 12,000 years ago, the warming climate caused large mammals, such as the mammoth, to become extinct. Humans who relied on these large animals for food had to turn to small game and plants.
The world experienced a brief cold period a number of years later. These few years of a very cold climate greatly affected the smaller game and the plant materials available as food sources. When the climate warmed again, humans adapted yet again to these changes. Human cultivation of domestic crops began about 10,000 years ago. They also domesticated some animals. These developments allowed the human population to grow despite limiting factors that normally keep species populations within the bounds of what an environment can support. Limiting factors include the availability of food, water, and shelter; predator/prey ratios; and the presence of pathogens. An environment’s carrying capacity is the maximum number of individuals it can support without leveling off. When the population of a species exceeds the carrying capacity, a crash, or rapid decline in population to well below the carrying capacity, usually occurs. A species that has genetic diversity usually rebounds, although it still might become extinct.
By cultivating crops and domestic animals for food, the human population was able to grow substantially and well beyond the environment’s carrying capacity by the early first century CE. At the end of the first century CE, the earth was populated by about 170 million people. The population increased to about 1 billion by 1800. The human population increased substantially due to the Industrial Revolution of the nineteenth century, reaching an estimated 1.6 billion in 1900. More recent developments, such as medical care and sanitation improvements, have greatly increased life expectancy, leading to increasing population. Birth rates in many parts of the world have continued to climb as well. In 2022, the United Nations announced that the world population reached 8 billion.
Overview
Deforestation, hunting, overfishing, and other human activities threaten up to one million plant and animal species. Human actions cause pollution and climate change, which threaten species. Human trade spreads diseases and invasive species, which threaten local populations.
Human activity has greatly increased the rate of extinction. The natural rate of extinction is about one to five species a year. In the early twenty-first century, scientists estimated dozens of species were going extinct every day. Some researchers believe between 30 and 50 percent of all extant species could go extinct by the middle of the century. In the previous five centuries, about one thousand known species went extinct.
Habitat destruction is the leading cause of species extinction. Many acres of natural habitats are destroyed to create farmland. Thousands of square miles of forest in the Amazon has been cleared annually for cattle farming, for example. Every year the skies over Indonesia become blackened by smoke as workers illegally burn off forest for farming. The average annual rate of deforestation in Indonesia was 530 square miles.
Biological diversity, or biodiversity, is important to protecting species from extinction. Biodiversity enables a species to survive extinction-level threats such as disease. Species with high genetic diversity, and multiple populations in different areas, are better prepared to survive threats such as disease, climate change, natural disasters, or loss of habitat. As an example, the platypus, Ornithorhynchus anatinus, is the only extant species in the family Ornighorhynchidae. It is found in the wild only in Australia, Tasmania, and King Island, with a small population introduced on South Australia’s Kangaroo Island. Multiple populations live in several river systems; this range contributes to species survival. However, lack of genetic diversity endangers the platypus. For example, during the 1980s, researchers noticed platypuses in the Elizabeth River in northern Tasmania were developing skin ulcers. The cause was found to be a fungus, Mucor amphibiorum, which infects and kills many frogs and toads. The fungus, which may have been introduced with the transport of frogs from the mainland, has since spread to many platypus populations in Tasmania. The infection endangers the population because the ulcers can become infected and kill the animals. Lack of genetic diversity means most if not all populations of the platypus may be susceptible to the fungus. For similar reasons, it is important to maintain biodiversity of food crops. Reliance on a few or even one species of a food crop could significantly affect a population if a fungus, disease, insect, or other concern threatens its survival. Human trade often introduces diseases and species into new areas where, like the platypus, the population is vulnerable.
Bibliography
Bagley, Mary. “Holocene Epoch: The Age of Man.” LiveScience, 27 Mar. 2013, www.livescience.com/28219-holocene-epoch.html. Accessed 7 Jan. 2020.
Carrington, Damian. “Humanity Has Wiped Out 60% of Animal Populations Since 1970, Report Finds.” The Guardian, 29 Oct. 2018, www.theguardian.com/environment/2018/oct/30/humanity-wiped-out-animals-since-1970-major-report-finds. Accessed 7 Jan. 2020.
Ceballos, Gerardo, Paul R. Ehrlich, and Rodolfo Dirzo. “Biological Annihilation Via the Ongoing Sixth Mass Extinction Signaled by Vertebrate Population Losses and Declines.” Proceedings of the National Academy of Sciences of the United States of America, vol. 114, no. 30, 25 July 2017, pp. E6089 – E6096. doi.org/10.1073/pnas.1704949114. Accessed 7 Jan. 2020.
“The Elements of Biodiversity.” Center for Biological Diversity, www.biologicaldiversity.org/programs/biodiversity/elements‗of‗biodiversity/index.html. Accessed 7 Jan. 2020.
“The Extinction Crisis.” Center for Biological Diversity, www.biologicaldiversity.org/programs/biodiversity/elements‗of‗biodiversity/extinction‗crisis/. Accessed 7 Jan. 2020.
Greshko, Michael, and National Geographic Staff. “What Are Mass Extinctions, and What Causes Them?” National Geographic, 26 Sept. 2019, www.nationalgeographic.com/science/prehistoric-world/mass-extinction/#close. Accessed 7 Jan. 2020.
Jong, Hans Nicholas. “Indonesia Forest-Clearing Ban Is Made Permanent, but Labeled ‘Propaganda.’” Mongabay, 14 Aug. 2019, news.mongabay.com/2019/08/indonesia-forest-clearing-ban-is-made-permanent-but-labeled-propaganda/. Accessed 7 Jan. 2020.
Phillips, Dom, et. al. “Revealed: Rampant Deforestation of Amazon Driven by Global Greed for Meat.” The Guardian, 2 July 2019, www.theguardian.com/environment/2019/jul/02/revealed-amazon-deforestation-driven-global-greed-meat-brazil. Accessed 7 Jan. 2020.
"World Population to Reach 8 Billion on 15 November 2022." United Nations, www.un.org/en/desa/world-population-reach-8-billion-15-november-2022. Accessed 7 Feb. 2025.