The human vermiform appendix is a vestigial structure: it no longer retains its original function.

Vestigial structures are anatomical structures of organisms in a species which are considered to have lost much or all of their original function through evolution. These structures are typically in a degenerate, atrophied, or rudimentary condition or form. Vestigial structures are often referred to as vestigial organs, though not all of them are actually organs. Image File history File links Gray536. ... Image File history File links Gray536. ... In human anatomy, the vermiform appendix (or appendix, pl. ... Anatomical drawing of the human muscles from the Encyclopédie. ... In biology and ecology, an organism (in Greek organon = instrument) is a living complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole. ... In biology, a species is one of the basic units of biodiversity. ... A hypothetical phylogenetic tree of all extant organisms, based on 16S rRNA gene sequence data, showing the evolutionary history of the three domains of life, bacteria, archaea and eukaryotes. ... In biology, an organ (Latin: organum, instrument, tool) is a group of tissues that perform a specific function or group of functions. ...

Although the structures most commonly referred to as "vestigial" tend to be largely or entirely functionless, a vestigial structure need not necessarily be without use or function for the organism. Vestigial structures have lost their original main purpose, but they may retain lesser functionalities, or develop entirely new ones.^[1] Thus, a "vestigial wing" need only be useless for flight to be vestigial; it may still serve some other purpose than that of a wing.

History

The blind mole rat (Spalax typhlus) has tiny eyes completely covered by a layer of skin.

Vestigial structures have been noticed since ancient times, and the reason for their existence has long been speculated upon. In the 4th century BC, Aristotle was one of the earliest writers to comment, in his History of Animals, on the vestigial eyes of moles, calling them "stunted in development". However, only in recent centuries have anatomical vestiges become a subject of serious study. In 1798, Étienne Geoffroy Saint-Hilaire noted on vestigial structures: Image File history File links Download high resolution version (1554x948, 381 KB) Original caption: Blindmaus, Spalax typhlus Pall. ... Image File history File links Download high resolution version (1554x948, 381 KB) Original caption: Blindmaus, Spalax typhlus Pall. ... Genera Nannospalax Spalax Blind mole rats are one of many types of rodents that are referred to as mole rats. ... Aristotle (Ancient Greek: , AristotélÄ“s) (384 BC – March 7, 322 BC) was an ancient Greek philosopher, a student of Plato and teacher of Alexander the Great. ... History of Animals (or Historia Animalium, or On the History of Animals) is a text by Aristotle. ... Étienne Geoffroy Saint-Hilaire (April 15, 1772 - June 19, 1844) was a French naturalist who established the principle of unity of composition. He was born at Étampes, Seine-et-Oise, and studied at the college of Navarre, in Paris, where he studied natural philosophy under M. J. Brisson. ...

Whereas useless in this circumstance, these rudiments... have not been eliminated, because Nature never works by rapid jumps, and She always leaves vestiges of an organ, even though it is completely superfluous, if that organ plays an important role in the other species of the same family.^[2]

His colleague, Jean-Baptiste Lamarck, named a number of vestigial structures in his 1809 book Philosophie Zoologique. Lamarck noted "Olivier's Spalax, which lives underground like the mole, and is apparently exposed to daylight even less than the mole, has altogether lost the use of sight: so that it shows nothing more than vestiges of this organ."^[3] Jean-Baptiste Lamarck Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck (August 1, 1744 – December 28, 1829) was a French naturalist and an early proponent of the idea that evolution occurred and proceeded in accordance with natural laws. ... Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck (August 1, 1744 - December 28, 1829) was a major 19th century naturalist, who was one of the first to use the term biology in its modern sense. ... Guillaume-Antoine Olivier (1756 - 1814) was a French entomologist. ... Genera Nannospalax Spalax Blind mole rats are one of many types of rodents that are referred to as mole rats. ...

Charles Darwin was very familiar with the concept of vestigial structures, though the term for them did not yet exist. He listed a number of them in The Descent of Man, including the muscles of the ear, wisdom teeth, the appendix, the tail bone, body hair, and the semilunar fold in the corner of the eye. Darwin also noted, in The Origin of Species, that a vestigial structure could be useless for its primary function, but still retain secondary anatomical roles: "An organ serving for two purposes, may become rudimentary or utterly aborted for one, even the more important purpose, and remain perfectly efficient for the other.... [A]n organ may become rudimentary for its proper purpose, and be used for a distinct object."^[4] Charles Robert Darwin (12 February 1809 – 19 April 1882) was an English naturalist who achieved lasting fame by producing considerable evidence that species originated through evolutionary change, at the same time proposing the scientific theory that natural selection is the mechanism by which such change occurs. ... The Descent of Man, and Selection in Relation to Sex was a book on evolutionary theory by British naturalist Charles Darwin, first published in 1871. ... Wisdom teeth are third molars that usually appear between the ages of 17 and 24 (although they may appear when older, younger, or may not appear at all). ... Appendix can mean: Appendix (see Book design), part of the content of some books vermiform appendix, a human internal organ, physically part of the digestive system but which function is a matter of controversy See also Look up appendix in Wiktionary, the free dictionary. ... The coccyx, commonly referred to as the tailbone, is the final segment of the human vertebral column, of three to five (usually four) fused vertebrae (the coccygeal vertebrae), below the sacrum. ... Hair is also a musical: see Hair (musical) and Hair (movie) Hair is the filamentous outgrowth of the epidermis found in mammals. ... Many species of land animals have a nictitating membrane, which can move across the eyeball to give the sensitive eye structures additional protection in particular circumstances. ... This article refers to the sight organ. ... The title page of the 1859 edition of On the Origin of Species. ...

In 1893, Robert Wiedersheim published a list of 86 human organs that had, in his words, "lost their original physiological significance". Theorizing that they were vestiges of evolution, he called them "vestigial".^[5] Since his time, the function of some of these structures has been discovered, while other anatomical vestiges have been unearthed, making the list primarily of interest as a record of the knowledge of human anatomy at the time. Later versions of Wiedersheim's list were expanded to as many as 180 human "vestigial organs". This is why the zoologist Newman stated in the Scopes Monkey Trial that "There are, according to Wiedersheim, no less than 180 vestigial structures in the human body, sufficient to make of a man a veritable walking museum of antiquities."^[6] Robert Wiedersheim (1848 – 1932) was a German anatomist who is famous for publishing a list of 86 “vestigial organs” in 1893. ... The Scopes Trial of 1925 pitted William Jennings Bryan against Clarence Darrow and teacher John T. Scopes in an American court case that tested a law passed on March 13, 1925, forbidding the teaching of evolution in Tennessee public schools. ...

Evidence of evolution

Main article: Evidence of evolution

Vestigial structures are often homologous to structures that are functioning normally in other species. Therefore, vestigial structures can be considered evidence for evolution, the process by which beneficial heritable traits arise in population over an extended period of time. The existence of vestigial organs can be attributed to changes in the environment and behavior patterns of the organism in question. As the function of the structure is no longer beneficial for survival, the likelihood that future offspring will inherit the "normal" form of the structure decreases. // Headline text This article or section seems not to be written in the formal tone expected of an encyclopedia entry. ... In biology, two or more structures are said to be homologous if they are alike because of shared ancestry. ... A hypothetical phylogenetic tree of all extant organisms, based on 16S rRNA gene sequence data, showing the evolutionary history of the three domains of life, bacteria, archaea and eukaryotes. ...

The vestigial versions of the structure can be compared to the original version of the structure in other species in order to determine the homology of a vestigial structure. Homologous structures indicate common ancestry with those organisms that have a functional version of the structure.^[7]

In humans

The muscles connected to the ears of a human do not develop enough to have the same mobility allowed to monkeys.

Although the list of human vestigial structures is still more or less the same, the relative usefulness of certain structures on the list is a subject of debate. The following are some of the structures often included in this list: Image File history File links Download high resolution version (1011x706, 113 KB) Derived by LP from Image:Ear_with_earring. ... Image File history File links Download high resolution version (1011x706, 113 KB) Derived by LP from Image:Ear_with_earring. ...

The vermiform appendix is a vestige of the cecum, an organ that was used to digest cellulose by humans' herbivorous ancestors. Analogous organs in other animals similar to humans continue to perform that function, whereas other meat-eating animals may have similarly diminished appendices. The modern functionality of the appendix is still controversial in the field of human physiology, although most scientists and physicians believe that it has little or no function. In human anatomy, the vermiform appendix (or appendix, pl. ... In anatomy of the digestive system, the cecum or caecum is a pouch connected to the large intestine between the ileum. ...

The coccyx, or tailbone, is the remnant of a lost tail. All mammals have a tail at one point in their development; in humans, it is present for a short time during embryonic development. The tailbone, located at the end of the spine, has lost its original function in assisting balance and mobility, though it still serves some secondary functions, such as being an attachment point for muscles, which explains why it has not degraded further. The coccyx is formed of four fused vertebrae. ... A Ring-tailed Lemur For other uses, see Tail (disambiguation). ... Embryos (and one tadpole) of the wrinkled frog (Rana rugosa). ...

The plica semilunaris is small fold of tissue on the inside corner of the eye. It is the vestigial remnant of the nictitating membrane (the "third eyelid") which is present in other animals. Many species of land animals have a nictitating membrane, which can move across the eyeball to give the sensitive eye structures additional protection in particular circumstances. ...

Wisdom teeth are vestigial third molars that humans' ancestors used to help in grinding down plant tissue. It has been proven that the skulls of human ancestors had larger jaws with more teeth, which were probably used to help chew down foliage to compensate for a lack of ability to efficiently digest the cellulose that makes up a plant cell wall. As humankind's diet changed, a smaller jaw was selected for by evolution, but the third molars, or "wisdom teeth", still commonly grow in.^[8] Wisdom teeth are third molars that usually appear between the ages of 17 and 24 (although they may appear when older, younger, or may not appear at all). ... Selection is hierachically classified into natural and artificial selection. ...

Goose bumps are an example of a vestigial human reaction to stress.

Humans also bear some vestigial behaviors and reflexes. For example, the formation of goose bumps in humans under stress is a vestigial reflex; its purpose in humans' evolutionary ancestors was to raise hair to make the animal appear bigger and scare off enemies. Raising the hair is also used to trap an extra layer of air, to keep the animal warm. This reflex formation of goosebumps when cold is not vestigial in humans, but the reflex to form them under stress is. Image File history File links Download high resolution version (561x800, 90 KB) Summary Photo of human goose bumps, from the German Wikipedia [1] This is maskara Licensing Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ... Image File history File links Download high resolution version (561x800, 90 KB) Summary Photo of human goose bumps, from the German Wikipedia [1] This is maskara Licensing Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ... Goose bumps on a human Goose bumps (AE), also called goose pimples, goose flesh (BE), chicken skin (Hawaiian Pidgin), or cutis anserina, are the bumps on a persons skin at the base of body hairs which involuntarily develop when a person is cold or experiences strong emotions like fear. ... Goose bumps, also called goose pimples, goose flesh, or cutis anserina, are the bumps on a persons skin at the base of body hairs (typically on the forearm), which involuntarily develop when a person is cold, afraid, or experiences other strong emotions. ... now. ... The mechanism of the reflex arc A reflex action is a stereotyped (involuntary) motor response elicited by a defined stimulus. ...

The ears of a Macaque monkey and most other monkeys, have far more developed muscles than those of humans and therefore have the capability to move their ears to better hear potential threats.^[9] This inability is compensated mainly by the ability of humans to turn their heads on a horizontal plane, an ability which is not common to most apes. Therefore, a function once provided by one structure is now replaced by another.^[10]

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, such as the nipple, may be more or less useless in the other, but not harmful enough to be selected against. These become vestigial traits in one sex. The clitoris has been described as a vestigial penis by some scientists, such as Stephen Jay Gould. Look up Sex in Wiktionary, the free dictionary. ... In biology, two or more structures are said to be homologous if they are alike because of shared ancestry. ... The udder of a cow with nipples showing In its most general form, a nipple is an appurtenance from which a fluid emanates, in this instance breast milk, to nurture a mothers young. ... A womans clitoris extends from the visible portion to a point below the pubic bone. ... The penis (plural penises, penes) is an external male sexual organ. ... Stephen Jay Gould Stephen Jay Gould (September 10, 1941 – May 20, 2002) was an American paleontologist, evolutionary biologist, and historian of science. ...

There are also vestigial molecular structures in humans, which are no longer in use but may indicate common ancestry with other species. One example of this is L-gulono-gamma-lactone oxidase, a gene, found functional in most other mammals, which produces a Vitamin C-catalyzing enzyme. In humans, an earlier mutation may have caused it to become disabled (unable to produce the enzyme), and it now remains in the human genome only as a vestigial genetic sequence.^[11] The human genome is the genome of Homo sapiens. ...

In other organisms

Letter c in the picture indicates the undeveloped hind legs of a baleen whale.

In whales and other cetaceans, one can find small vestigial leg bones deeply buried within the back of the body. These are remnants of their land-living ancestors' legs. Many whales also have undeveloped, unused, pelvis bones in the anterior part of their torsos. Image File history File links Skelett_vom_Wal_MK1888_ohne_Text. ... Image File history File links Skelett_vom_Wal_MK1888_ohne_Text. ... Families Balaenidae Balaenopteridae Eschrichtiidae Neobalaenidae Scientifically known as the Mysticeti, the baleen whales, also called whalebone whales or great whales, form a suborder of the order cetacea. ... Whales are the largest species of exclusively aquatic mammals, members of the order Cetacea, which also includes dolphins and porpoises. ... Suborders Mysticeti Odontoceti (see text) The order Cetacea includes whales, dolphins and porpoises. ... Human male pelvis, viewed from front Human female pelvis, viewed from front The pelvis is the bony structure located at the base of the spine (properly known as the caudal end). ... In zootomy, several terms are used to describe the location of organs and other structures in the body of bilateral animals. ...

Penguins and Dodo birds (now extinct) have hollow bones, a feature usually reserved for flying birds. (The weight reduction is crucial to staying in the air. Since both birds don't fly, having hollow bones is unneeded, and therefore vestigial.^[12]) The wings of ostriches, emus, and other flightless birds are vestigial; they are remnants of their flying ancestors' wings. Modern Genera Aptenodytes Eudyptes Eudyptula Megadyptes Pygoscelis Spheniscus For extinct genera, see Systematics Penguins (order Sphenisciformes, family Spheniscidae) are an order of aquatic, flightless birds living in the Southern Hemisphere. ... Binomial name Raphus cucullatus (Linnaeus, 1758) Former range (in red) The Mauritius Dodo (Raphus cucullatus, called Didus ineptus by Linnaeus), more commonly just Dodo, was a metre-high flightless bird of the island of Mauritius. ... Binomial name Struthio camelus Linnaeus, 1758 The ostrich (Struthio camelus) is a flightless bird native to Africa. ... Binomial name Dromaius novaehollandiae (Latham, 1790) Synonyms Dromiceius novaehollandiae Emu (IPA pronunciation: ), Dromaius novaehollandiae, is the largest bird native to Australia and the only extant member of the genus Dromaius. ... Flightless birds evolved from flying ancestors; there are about forty species in existence today. ...

The eyes of certain cavefish and salamanders are vestigial, as they no longer allow the organism to see, and are remnants of their ancestors' functional eyes. Genera  Amblyopsis  Chologaster  Forbesichthys  Speoplatyrhinus  Typhlichthys The cavefishes are a family Amblyopsidae of fish found in caves and adapted to life in the dark, notably lacking eyes and of a pale or white color. ...

Crabs have small tails tucked between their rear legs that are probably vestigial, as they are no longer in use. The working version of these tails can be found in their close crustacean relative, the lobster.^[12] Phthirus pubis Pubic lice (Phthirus pubis), also known as crabs , are one of the many varieties of lice (singular louse) specialized to live on different areas of different animals. ... Classes & Subclasses Branchiopoda Phyllopoda Sarsostraca Remipedia Cephalocarida Maxillopoda Thecostraca Tantulocarida Branchiura Pentastomida Mystacocarida Copepoda Ostracoda Myodocopa Podocopa Malacostraca Phyllocarida Hoplocarida Eumalacostraca The crustaceans (Crustacea) are a large group of arthropods (55,000 species), usually treated as a subphylum [1]. They include organisms such as lobsters, crabs, shrimp and barnacles. ... Subfamilies and Genera Neophoberinae Acanthacaris Thymopinae Nephropsis Nephropides Thymops Thymopsis Nephropinae Homarus Nephrops Homarinus Metanephrops Eunephrops Thymopides Clawed lobsters comprise a family (Nephropidae, sometimes also Homaridae) of large marine crustaceans. ...

Vestigial structures are not only found in animals; plants also are known to have vestigial parts. Dandelions and other asexually reproducing plants produce unneeded flower petals. These petals were once used to attract pollinating insects, but are now no longer needed.^[12] Species Taraxacum officinale Taraxacum japonicum Taraxacum albidum and a few others. ... Asexual reproduction in liverworts: a caducuous phylloid germinating Asexual reproduction (also known as agamogenesis) is a form of reproduction which does not involve meiosis, gamete formation, or fertilization. ...

Grass and other non-flowering angiosperms often have small, undeveloped structures which strongly resemble those of flowering plants.^[12] An area of grass-like plants Grass generally describes a monocotyledonous green plant characterized by slender leaves, called blades, which usually grow arching upwards from the ground. ... Classes Magnoliopsida - Dicots Liliopsida - Monocots The flowering plants (also angiosperms or Magnoliophyta) are one of the major groups of modern plants, comprising those that produce seeds in specialized reproductive organs called flowers, where the ovulary or carpel is enclosed. ...

The eyes of a flounder start off on either side of the flounder's head. Shortly after birth, one of the eyes moves around to the other side of the fish's head.^[12] Winter flounder, Pseudopleuronectes americanus Flounder are flatfish that live in ocean waters in Northern European waters and along the east coast of the United States and Canada, as well as the western Pacific (Japan). ...

Fruit flies have been known to occasionally grow legs where their antennae should be. This suggests that the antennae and legs have a similar origin, or that during development appendages are signaled to develop into their respective forms. In this case, it is possible the signal did not occur correctly.^[12] Species Drosophila melanogaster Drosophila subobscura Drosophila is a genus of small flies whose members are often called fruit flies or more appropriately vinegar flies, wine flies, pomace flies, grape flies, and picked fruit-flies. ...

Certains species of moths (for example the Gypsy moth) have females that although flightless, still carry small wings. These wings have no use, and are vestigial to the versions in species whose females can fly.^[12] Lepidopteran on a flower. ... Binomial name Lymantria dispar Linnaeus, 1758 This article deals with the moth Lymantria dispar. ...

Controversy

Because vestigial organs are used as supporting evidence for evolution, some creationists oppose the validity of the idea. They question whether these organs are actually useless, since they believe that God gave each organism its organs for a specific reason and use. A hypothetical phylogenetic tree of all extant organisms, based on 16S rRNA gene sequence data, showing the evolutionary history of the three domains of life, bacteria, archaea and eukaryotes. ... The Creation of Light by Gustave Doré. In many religious traditions, creationism is the active acceptance of an origin belief that humanity, life, the Earth, or the universe as a whole was specially created by a supreme being or by supernatural intervention. ... God is the deity believed by monotheists to be the supreme reality. ...

Those who question the existence of vestigial organs usually claim a different definition for vestigial, giving a strict interpretation that an organ must be utterly useless to qualify.^[13] This is a definition often used in dictionaries^[14] and children's encyclopedias.^[15] Biology textbooks^[16][17] and scientific encyclopedias^[1] usually describe an organ 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 (preadaptation). In biology, two or more structures are said to be homologous if they are alike because of shared ancestry. ... In evolutionary biology, preadaptation describes a situation where an organism uses a preexisting anatomical structure inherited from an ancestor for a potentially unrelated purpose. ...

Those who consider the true meaning of vestigial to be "completely without use" tend to claim that the meaning has been changed over time as structures thought to be vestigial were found to have other uses.^[18] However, documentation indicates that from the theory's beginnings in the 19th century, vestigial structures have invariably been understood to "sometimes retain their potentiality"^[19], becoming either "wholly or in part functionless".^[20] It was thought that "not infrequently the degenerating organ can be turned to account in some other way".^[21]

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. The gas bladder (also fish maw, less accurately swim bladder or air bladder) is an internal organ that contributes to the ability of a fish to control its buoyancy, and thus to stay at the current water depth, ascend, or descend without having to waste energy in swimming. ... The lungs flank the heart and great vessels in the chest cavity. ... Orders See text The Actinopterygii are the ray-finned fish. ...

See also

• Dewclaw
• Plantaris muscle
• Atavism
• Dandelion

The dogs front dewclaw grows on the side of the foot, above the other four toes but below the rear heelpad. ... The Plantaris muscle is a muscle of the human body. ... An atavism can mean an organism that is a real or supposed evolutionary throwback; the unexpected appearance of primitive traits; or a reversion to or reappearance of a trait that had been present in a lineage in the past, but which had been absent in intervening generations. ... Species See text. ...

References

Étienne Geoffroy Saint-Hilaire (April 15, 1772 - June 19, 1844) was a French naturalist who established the principle of unity of composition. He was born at Étampes, Seine-et-Oise, and studied at the college of Navarre, in Paris, where he studied natural philosophy under M. J. Brisson. ... Jean-Baptiste Lamarck Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck (August 1, 1744 – December 28, 1829) was a French naturalist and an early proponent of the idea that evolution occurred and proceeded in accordance with natural laws. ... Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck (August 1, 1744 - December 28, 1829) was a major 19th century naturalist, who was one of the first to use the term biology in its modern sense. ... Charles Robert Darwin (12 February 1809 – 19 April 1882) was an English naturalist who achieved lasting fame by producing considerable evidence that species originated through evolutionary change, at the same time proposing the scientific theory that natural selection is the mechanism by which such change occurs. ... The title page of the 1859 edition of On the Origin of Species. ... Robert Wiedersheim (1848 – 1932) was a German anatomist who is famous for publishing a list of 86 “vestigial organs” in 1893. ...

External links

• Article relating to vestigial clitoris controversy
• talk origins page on vestigial organs