More than five billion species have already vanished from Earth
Extinction is the normal fate of life: a typical species disappears within about 10 million years of first appearing, and over five billion have died out. What is unusual now is the pace. A 2019 global assessment found wild mammal biomass down 82 percent and a million species at risk, largely because of human activity.
Formally, a species is extinct when its last member dies. It can be doomed earlier, though: functional extinction sets in when the few survivors cannot breed because they are too old, too sick, too scattered, or all one sex. Because ranges can be vast, the moment of disappearance is usually fixed only in hindsight, which is why so-called Lazarus taxa can seem to return, typically in the fossil record, after a long absence. Declaring extinction also demands a clear definition of the species, distinct from its ancestors and descendants; such replacements are central to the punctuated equilibrium idea of Stephen Jay Gould and Niles Eldredge.
Isolated losses are a routine part of evolution, and mass extinctions are rare. The present one is different in cause. Some scientists estimate that up to half of today's plants and animals could be gone by 2100. A 2018 report calculated that restoring the evolutionary diversity of 300 mammal species lost since the Late Pleistocene would take 5 to 7 million years. At least 571 plant species have disappeared since 1750, and most species that die out are never described by science at all.
The IPBES panel identifies habitat destruction, such as clearing forests for farmland, as the main driver, alongside unsustainable fishing, hunting and logging. Natural ecosystems have lost roughly half their area, and a quarter of plant and animal species are threatened.
Losses can be local rather than global. A species may vanish from one area yet survive elsewhere, and reintroductions such as bringing back wolves can repair the gap. At the other end, the category 'extinct in the wild' covers species surviving only in zoos or similar settings. Some of these are effectively gone, but planned breeding programmes aim to keep viable populations for a possible return to their habitat.
Source: Extinction
