Extinction and the IUCN Red List

Extinction is the permanent disappearance of a species, so that not a single living individual of it remains anywhere on Earth. The fossil record shows that extinction is not, in itself, an unusual event in the long sweep of Earth's history -- the vast majority of all species that have ever existed are already extinct -- but the geological record also documents five exceptionally severe mass extinction events, spread across hundreds of millions of years, in each of which a very large proportion of all species living at the time died out within a relatively short geological interval, generally attributed to major natural planetary events such as asteroid impacts or prolonged volcanic activity. Many biologists now argue that the world is in the midst of a sixth mass extinction episode, but one that is different in a fundamental respect from the previous five: it is being driven overwhelmingly by the activities of a single species, humans, rather than by an external natural catastrophe.

Current estimates suggest that species are now going extinct at somewhere between about 100 and 1,000 times the natural background extinction rate that prevailed before large-scale human impact on the planet -- an extraordinarily rapid pace, considering how comparatively rare extinction was over most of Earth's geological history. If the present rate of loss continues unchecked, some ecologists have projected that as much as half of all species alive today could be lost within the coming century, a sobering estimate that has driven much of the urgency behind modern conservation efforts. …