Pronunciation:eks-TIN-ktshun

Etymology: Extinction is derived from the Latin verb extinguere, which means to extinguish.

Extinction is the disappearance of a species or a population. This can occur through a variety of means. Generally, species with small numbers are in the greatest danger of extinction. However, even large populations can become extinct gradually through changes in local environments which prevent members of a species to reproduce well enough to replace themselves. Such extinctions might occur through competition with other species for limited resources or through a disease that the species cannot combat (e.g. American Chestnut). The Passenger Pigeon, a native North American bird was so abundant during the 19th century that flocks blocked out the sun, but through overhunting and habitat destruction, the species was extinct before World War I.

Mass extinctions are sudden, at least on a geological scale, and impact many species. Perhaps the most celebrated mass extinction occurred 65 million years ago when a bolide the size of Mt. Everest struck the Gulf of Mexico and led to the extinction of about 70% of the taxa on earth, including the dinosaurs. The greatest extinction occurred at the end of the Permian Period in which >90% of all taxa on earth disappeared over a 5 million year period.

Now, through pollution, overharvesting, habitat destruction, and anthropogenic climate change, we are in the midst of a mass extinction. This time, however, the global extinction is being caused by the actions of a single species, Homo sapiens.

Extinctions do leave open niches which might be filled by the evolution of new species. Over many millions of years, the open niches left after the extinction of the dinosaurs encouraged the evolution and diversity of many groups of mammals. Some uninformed citizens point their fingers at that as an example of how our species is doing the earth a favor by encouraging evolution. Such foolish statements do not take into account the relative temporal scales of human lifetimes, or even human civilizations, and of the time to evolve new species. Indeed, the background of biodiversity on this planet is part of our environment. The lesson the Passenger Pigeon is that even a large and successful species can disappear suddenly if its environment changes enough.

By Jack R. Holt. Last revised: 01/02/2009