Extinction

Extinction is the end of a species: the point at which its last individual dies, leaving no members anywhere on Earth. It is a normal part of the history of life. The great majority of species that have ever lived are now extinct, and the number of species alive at any time reflects a balance between extinction and speciation, the formation of new species.

Species disappear at a slow, steady background rate when they cannot cope with changes in climate, competitors, predators or disease. At a few points in Earth's history the rate has jumped sharply in mass extinctions, which wiped out a large share of species in a geologically short time and opened space for surviving groups to diversify. Small populations and species with narrow ranges or specialized needs are most at risk, and the loss of one species can threaten others that depend on it.

Today, species are disappearing far faster than the background rate, mainly because of human activity: habitat destruction, introduced species, overharvesting, pollution and climate change. Familiar losses from recent centuries include the dodo, Steller's sea cow and the passenger pigeon.