Extinction

Extinction occurs when a species has no surviving individuals anywhere on Earth. The definition applies to wild populations and, in conservation practice, generally also considers whether individuals survive only in captivity or cultivation.² A population can vanish from one region while remaining elsewhere; this is called extirpation or local extinction. A species may also be considered functionally extinct when its population is too small, fragmented, or old to sustain reproduction, even though a few organisms remain.

Extinction is not limited to familiar animals. It can affect plants, fungi, microorganisms, subspecies, and genetically distinct lineages. The disappearance of a population may remove unique adaptations before the entire species is lost, reducing genetic diversity and weakening resilience. Fossils show that extinction has always accompanied evolution, because lineages eventually disappear as environments change, competitors arise, or chance events eliminate small populations.

Human pressure is now the dominant cause of most recent documented extinctions. Land- and sea-use change destroys or fragments habitat; hunting, fishing, and wildlife trade remove organisms faster than they can reproduce; introduced species alter food webs and transmit diseases; and pollution damages organisms and ecosystems. Climate change adds heat, drought, altered seasons, ocean warming, and acidification, often interacting with the other pressures rather than acting alone.³

Risk is unevenly distributed. Species with small ranges, specialized diets, slow reproduction, large body size, or dependence on particular habitats are especially vulnerable. Island species often face severe danger because they evolved without many predators and have limited room for populations to retreat. A small population can enter an extinction vortex: inbreeding, demographic chance, and environmental shocks reinforce one another until recovery becomes unlikely.

Mass extinctions are unusually rapid losses of biodiversity across many unrelated groups. The end-Cretaceous event, associated with the Chicxulub asteroid impact and other environmental stresses, eliminated non-avian dinosaurs and many marine and terrestrial species. Such events differ from the slower background extinction that normally occurs between crises.

Scientists cannot count every extinction directly, so conservation assessments combine surveys, historical records, population models, and evidence about habitat and threats. The International Union for Conservation of Nature classifies species from Least Concern to Extinct using criteria involving population decline, geographic range, population size, and extinction probability.⁴ Absence of observations is not by itself proof of extinction, especially for cryptic, deep-sea, or poorly studied organisms.

Prevention usually begins with protecting and reconnecting habitat, controlling exploitation, managing invasive species, reducing pollution, and addressing climate change. Recovery may involve captive breeding, seed banks, reintroduction, translocation, or genetic management. These methods work best when the original threats have been removed. Legal protection can be decisive: the United States Endangered Species Act, for example, supports habitat protection and recovery planning, although implementation varies among cases.⁵

Conservation decisions sometimes involve triage because money, time, and suitable habitat are limited. Protecting an entire ecosystem can preserve many species at once, while targeted action may be necessary for a single species with an unusual or irreplaceable evolutionary history.

Plant extinctions are substantially under-recorded because botanists have fewer historical observations for many regions, and some plants persist unnoticed as seeds or underground structures. A global review reported 571 confirmed plant extinctions between 1753 and 2018, with the highest concentration on islands and in tropical regions. The figure illustrates both the scale of loss and the difficulty of detecting it.

Extinction can also proceed through ecological disappearance before biological disappearance. A species may survive in tiny numbers but no longer disperse seeds, control prey, build habitat, or perform pollination. Conversely, a species presumed extinct may be rediscovered—the so-called Lazarus effect—although rediscovery does not necessarily mean that its population is secure.

Genomic methods are refining the boundary between species survival and loss by identifying overlooked populations and extinct genetic lineages. De-extinction proposals, usually involving genetic engineering or selective breeding, cannot recreate an extinct species in its exact historical form; any resulting organism would have a new genome, ecological role, and conservation obligations. Preventing extinction therefore remains more reliable than attempting to reverse it.

Extirpation

The disappearance of a species from a particular geographic area while it survives elsewhere.

Functional extinction

A condition in which a species persists in very small numbers but no longer performs a viable reproductive or ecological role.

Extinction vortex

A self-reinforcing decline in which small population size increases inbreeding, demographic instability, and vulnerability to environmental change.

Mass extinction

A geologically brief interval in which unusually large numbers of species disappear across many groups.

De-extinction

Efforts to create organisms resembling extinct species through methods such as genetic engineering, cloning, or selective breeding.