Vestigial organ

From Academic Kids

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.

Some debate occurs regarding the definition for "vestigial", with some claiming a strict interpretation that an organ must be utterly useless to classify. Others claim that 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 of the dispute 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.

Because vestigial organs are used as supporting evidence for evolution, creationists vigorously oppose the idea.

Definition

Organs or structures remaining or surviving in a degenerate, atrophied, or imperfect condition or form.

External links

Navigation

Academic Kids Menu

  • Art and Cultures
    • Art (http://www.academickids.com/encyclopedia/index.php/Art)
    • Architecture (http://www.academickids.com/encyclopedia/index.php/Architecture)
    • Cultures (http://www.academickids.com/encyclopedia/index.php/Cultures)
    • Music (http://www.academickids.com/encyclopedia/index.php/Music)
    • Musical Instruments (http://academickids.com/encyclopedia/index.php/List_of_musical_instruments)
  • Biographies (http://www.academickids.com/encyclopedia/index.php/Biographies)
  • Clipart (http://www.academickids.com/encyclopedia/index.php/Clipart)
  • Geography (http://www.academickids.com/encyclopedia/index.php/Geography)
    • Countries of the World (http://www.academickids.com/encyclopedia/index.php/Countries)
    • Maps (http://www.academickids.com/encyclopedia/index.php/Maps)
    • Flags (http://www.academickids.com/encyclopedia/index.php/Flags)
    • Continents (http://www.academickids.com/encyclopedia/index.php/Continents)
  • History (http://www.academickids.com/encyclopedia/index.php/History)
    • Ancient Civilizations (http://www.academickids.com/encyclopedia/index.php/Ancient_Civilizations)
    • Industrial Revolution (http://www.academickids.com/encyclopedia/index.php/Industrial_Revolution)
    • Middle Ages (http://www.academickids.com/encyclopedia/index.php/Middle_Ages)
    • Prehistory (http://www.academickids.com/encyclopedia/index.php/Prehistory)
    • Renaissance (http://www.academickids.com/encyclopedia/index.php/Renaissance)
    • Timelines (http://www.academickids.com/encyclopedia/index.php/Timelines)
    • United States (http://www.academickids.com/encyclopedia/index.php/United_States)
    • Wars (http://www.academickids.com/encyclopedia/index.php/Wars)
    • World History (http://www.academickids.com/encyclopedia/index.php/History_of_the_world)
  • Human Body (http://www.academickids.com/encyclopedia/index.php/Human_Body)
  • Mathematics (http://www.academickids.com/encyclopedia/index.php/Mathematics)
  • Reference (http://www.academickids.com/encyclopedia/index.php/Reference)
  • Science (http://www.academickids.com/encyclopedia/index.php/Science)
    • Animals (http://www.academickids.com/encyclopedia/index.php/Animals)
    • Aviation (http://www.academickids.com/encyclopedia/index.php/Aviation)
    • Dinosaurs (http://www.academickids.com/encyclopedia/index.php/Dinosaurs)
    • Earth (http://www.academickids.com/encyclopedia/index.php/Earth)
    • Inventions (http://www.academickids.com/encyclopedia/index.php/Inventions)
    • Physical Science (http://www.academickids.com/encyclopedia/index.php/Physical_Science)
    • Plants (http://www.academickids.com/encyclopedia/index.php/Plants)
    • Scientists (http://www.academickids.com/encyclopedia/index.php/Scientists)
  • Social Studies (http://www.academickids.com/encyclopedia/index.php/Social_Studies)
    • Anthropology (http://www.academickids.com/encyclopedia/index.php/Anthropology)
    • Economics (http://www.academickids.com/encyclopedia/index.php/Economics)
    • Government (http://www.academickids.com/encyclopedia/index.php/Government)
    • Religion (http://www.academickids.com/encyclopedia/index.php/Religion)
    • Holidays (http://www.academickids.com/encyclopedia/index.php/Holidays)
  • Space and Astronomy
    • Solar System (http://www.academickids.com/encyclopedia/index.php/Solar_System)
    • Planets (http://www.academickids.com/encyclopedia/index.php/Planets)
  • Sports (http://www.academickids.com/encyclopedia/index.php/Sports)
  • Timelines (http://www.academickids.com/encyclopedia/index.php/Timelines)
  • Weather (http://www.academickids.com/encyclopedia/index.php/Weather)
  • US States (http://www.academickids.com/encyclopedia/index.php/US_States)

Information

  • Home Page (http://academickids.com/encyclopedia/index.php)
  • Contact Us (http://www.academickids.com/encyclopedia/index.php/Contactus)

  • Clip Art (http://classroomclipart.com)
Toolbox
Personal tools