Definition: Pertaining to a part of an animal that is no longer used and is, from an evolutionary perspective, in the process of being lost. Vestigal structures are often small and imperfectly formed—they usually serve little function or are no longer used by the organism.
The existence of vestigial characteristics is often used as a kind of evidence of evolution. A vestige has no function at present. Instead, it is a shadow of past adaptations and implies a continuous series of changes—it illustrates transition, the process of loosing a trait or part over time. And change through time is evolution.
Some illustrations of vestigial characteristics include are:
- Flightless birds such as penguins, the cormorants that inhabit the Galapagos Islands, kiwis, and ostriches have rudimentary wings even though they no longer fly.
- Many marine mammals such as whales and some skakes such as the boa constrictor have rudimentary bones of the pelvic girdle and thighbone even though they do not have hind limbs.
- Many cave-dwelling species who spend their lives in darkness have eyes, incapable of sight, burried beneath their skin.
- Pigs walk on only two toes per foot but they have two more toes that are higher on the leg and never touch the ground when walking.
References:
Keeton, W. and J. Gould. 1986. Biological Science, 14th Edition. New York: WW Norton & Company.
Examples:
Examples of vestigal structures are wings in ostriches and other flightless birds, hind limbs in cetaceans, and eyes in organisms that live entirely in the dark (such as cave-dwelling animals).
