in biology, disappearance of species of living organisms. Extinction usually occurs as a result of changed conditions to which the species is not suited. If no member of the affected species survives and reproduces, the entire line dies out, leaving no descendants. This was the case with the saber-toothed cat ( Smilodon
) of North America, which is not ancestral to any living species. However, a species may also become extinct through its gradual evolution
into a new species, as a result of natural selection for characteristics suited for new conditions. An example of the latter situation is the evolution of horses
from the eophippus ( Hyracotherium
) to Miohippus
to the present-day Equus.
There has been an unbroken line of descent, yet horses of the earlier types no longer exist. Human activities, such as overhunting a species or destroying its habitat, have caused the extinction of some species, such as the passenger pigeon
, and threatened many others (see endangered species
). See also mass extinction
See M. V. Barrow, Jr., Nature's Ghosts: Confronting Extinction from the Age of Jefferson to the Age of Ecology (2009); E. Fuller, Lost Animals: Extinction and the Photographic Record (2014).
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
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