A vestigial organ is an organ whose original function has been lost during evolution.

In 1893, Robert Wiedersheim published a list of 86 human organs that had no known function. Theorizing that they were vestiges of evolution, he called them "vestigial".

Today, the list of human vestigial organs is much smaller, and hotly debated. It still includes the appendix, and coccyx. Many people maintain that the coccyx is a remnant of a lost tail. Wisdom teeth are vestigial as well. Also, the plica semilunaris, the small fold of tissue on the inside corner of the eye, is the vestigial remnant of the nictitating membrane (the third eyelid) in other animals.

The formation of goose bumps in humans under emotional stress is a vestigial reflex; its purpose in our evolutionary ancestors was to raise hair to make the animal appear bigger and scare off enemies.

Some traits may be vestigial in one sex but not another because they are homologous but do not share similar functions between the sexes. Organs with a distinct purpose in one sex, for example the nipple, may be more or less useless in the other, but not harmful enough to be selected against. These become vesitigial traits in one sex. The clitoris has been described as a vestigial penis by some scientists, such as Stephen Jay Gould. Others argue that the clitoris serves an important reproductive function in female orgasm.

In whales and other cetaceans, one can find small vestigial leg bones deeply buried within the body; these are remnants of their land-living ancestors' legs. The wings of ostriches and emus are vestigial, remnants of their flying ancestors' wings.

Because vestigial organs are supporting evidence for evolution, creationists have vigorously attacked the idea, claiming that for an organ to be "vestigial" it must be utterly useless. This is a misrepresentation: an organ in a modern animal may be described as vestigial if it does not serve the same function in the modern animal as the cognate organ served in an ancestor, even if the modern organ serves a completely different use. An example is the gas bladder of many fish, which is thought to be a vestigial lung, "left over" from the occasionally-air-gasping common ancestor of ray-finned fish and land vertebrates.

External links

• Article relating to vestigial clitoris controversy (http://www.findarticles.com/p/articles/mi_m1175/is_n1_v29/ai_17955288)