What is a Vestige?

Question: What is a Vestige?

Answer:

The term vestige has a number of slightly different meanings based on the context of its use. Let's begin with the common definition of 'vestige' from the Collaborative International Dictionary of English:

"Vestige \Ves"tige\, n. The mark of the foot left on the earth; a track or footstep; a trace; a sign; hence, a faint mark or visible sign left by something which is lost, or has perished, or is no longer present."

Now let's extend its definition to the context of zoology. When used with respect to animals (and other organisms), the term vestige refers to an under-developed and often no-longer-used body part that was present in fully developed and functional form in past generations. Like the common definition above, the zoological definition of the term vestige refers to a remnant or trace of something that was once present but is possibly disappearing over successive generations.

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.

Sources

Keeton, W. and J. Gould. 1986. Biological Science, 14th Edition. New York: WW Norton & Company.