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Vestigiality is the retention, during the process of
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on comparison with homologous features in related species. The emergence of vestigiality occurs by normal evolutionary processes, typically by loss of function of a feature that is no longer subject to
positive Positive is a property of Positivity (disambiguation), positivity and may refer to: Mathematics and science * Converging lens or positive lens, in optics * Plus sign, the sign "+" used to indicate a positive number * Positive (electricity), a po ...

positive
selection pressures Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection. It is a quantitative description of the amount of c ...
when it loses its value in a changing environment. The feature may be selected against more urgently when its function becomes definitively harmful, but if the lack of the feature provides no advantage, and its presence provides no disadvantage, the feature may not be phased out by natural selection and persist across species. Examples of vestigial structures (also called degenerate, atrophied, or rudimentary organs) are the loss of functional wings in island-dwelling birds; the human
vomeronasal organ The vomeronasal organ (VNO), or Jacobson's organ, is the paired auxiliary olfactory (smell) sense organ located in the soft tissue of the nasal septum, in the nasal cavity just above the roof of the mouth (the hard palate). The name is derived fro ...

vomeronasal organ
; and the hindlimbs of the
snake Snakes are elongated, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Many species of snakes ...

snake
and
whale Whales are a widely distributed and diverse group of fully s. They are an informal grouping within the infraorder , which usually excludes s and s. Whales, dolphins and porpoises belong to the order , which consists of s. Their closest n ...

whale
. The human appendix is no longer considered vestigial.


Overview

Vestigial features may take various forms; for example, they may be patterns of behavior, anatomical structures, or biochemical processes. Like most other physical features, however functional, vestigial features in a given species may successively appear, develop, and persist or disappear at various stages within the
life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from birth to reproduction ending with the production of the offspring *Life-cycle hypothesis, ...
of the organism, ranging from early
embryonic development An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...
to late adulthood. Vestigiality, biologically speaking, refers to organisms retaining organs that have seemingly lost their original function. The issue is controversial and not without dispute; nonetheless, vestigial organs are common evolutionary knowledge. In addition, the term ''vestigiality'' is useful in referring to many genetically determined features, either morphological, behavioral, or physiological; in any such context, however, it need not follow that a vestigial feature must be completely useless. A classic example at the level of gross anatomy is the human
vermiform appendix The appendix (or vermiform appendix; also cecal r caecalappendix; vermix; or vermiform process) is a finger-like, blind-ended tube connected to the cecum, from which it prenatal development, develops in the embryo. The cecum is a pouch-like ...

vermiform appendix
—though vestigial in the sense of retaining no significant ''digestive'' function, the appendix still has immunological roles and is useful in maintaining
gut flora Gut or guts may refer to: Anatomy * Abdomen, the region of the body below the thorax but above the pelvic region * Beer gut, slang for an obese stomach * Gastrointestinal tract, the system of digestive organs in humans and other animals * Hu ...
. Similar concepts apply at the molecular level—some
nucleic acid Nucleic acids are biopolymers, macromolecules, essential to all Organism, known forms of life. They are composed of nucleotides, which are the monomers made of three components: a pentose, 5-carbon sugar, a phosphate group and a nitrogenous base. ...

nucleic acid
sequences in
eukaryotic Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...
genomes In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Mol ...
have no known biological function; some of them may be "
junk DNA Non-coding DNA sequences are components of an organism's DNA that do not encode protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins per ...
", but it is a difficult matter to demonstrate that a particular sequence in a particular region of a given genome is truly nonfunctional. The simple fact that it is
noncoding DNA Non-coding DNA sequences are components of an organism's DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of ...
does not establish that it is functionless. Furthermore, even if an extant DNA sequence is functionless, it does not follow that it has descended from an ancestral sequence of functional DNA. Logically such DNA would not be vestigial in the sense of being the vestige of a functional structure. In contrast
pseudogenes Pseudogenes are nonfunctional segments of DNA that resemble functional genes In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical proces ...
have lost their protein-coding ability or are otherwise no longer expressed in the cell. Whether they have any extant function or not, they have lost their former function and in that sense, they do fit the definition of vestigiality. Vestigial structures are often called ''vestigial organs'', although many of them are not actually
organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma Parenchyma () is the bulk of functional ...
. Such vestigial structures typically are degenerate, atrophied, or rudimentary, and tend to be much more
variable
variable
than homologous non-vestigial parts. Although structures commonly regarded "vestigial" may have lost some or all of the functional roles that they had played in ancestral organisms, such structures may retain lesser functions or may have become adapted to new roles in extant populations.Muller, G. B. (2002) "Vestigial Organs and Structures". in ''Encyclopedia of Evolution''. Mark Pagel, editor in chief, New York: Oxford University Press. pp. 1131–1133 It is important to avoid confusion of the concept of vestigiality with that of
exaptation Exaptation and the related term Co-option (biology), co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Ex ...
. Both may occur together in the same example, depending on the relevant point of view. In exaptation, a structure originally used for one purpose is modified for a new one. For example, the wings of
penguin Penguins (order (biology), order Sphenisciformes , family (biology), family Spheniscidae ) are a group of Water bird, aquatic flightless bird, flightless birds. They live almost exclusively in the southern hemisphere: only one species, the Gal ...

penguin
s would be exaptational in the sense of serving a substantial new purpose (underwater locomotion), but might still be regarded as vestigial in the sense of having lost the function of flight. In contrast Darwin argued that the wings of
emu The emu (''Dromaius novaehollandiae'') is the second-largest living bird by height, after its ratite relative, the ostrich. It is endemic Endemism is the state of a species In biology, a species is the basic unit of biological c ...

emu
s would be definitely vestigial, as they appear to have no major extant function; however, function is a matter of degree, so judgments on what is a "major" function are arbitrary; the emu does seem to use its wings as organs of balance in running. Similarly, the
ostrich ''Struthio'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a ...

ostrich
uses its wings in displays and temperature control, though they are undoubtedly vestigial as structures for flight. Vestigial characters range from detrimental through neutral to favorable in terms of selection. Some may be of some limited utility to an organism but still degenerate over time if they do not confer a significant enough advantage in terms of fitness to avoid the effects of
genetic drift Genetic drift (allelic drift or the Sewall Wright effect) is the change in the frequency of an existing gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, M ...

genetic drift
or competing selective pressures. Vestigiality in its various forms presents many examples of evidence for biological evolution.


History

Vestigial structures have been noticed since ancient times, and the reason for their existence was long speculated upon before
Darwinian evolution Darwinism is a theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as obser ...
provided a widely accepted explanation. In the 4th century BC,
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher A philosopher is someone who practices philosophy Philosophy (from , ) is the study of general and fundamental quest ...

Aristotle
was one of the earliest writers to comment, in his ''
History of Animals ''History of Animals'' ( grc-gre, Τῶν περὶ τὰ ζῷα ἱστοριῶν, ''Ton peri ta zoia historion'', "Inquiries on Animals"; la, Historia Animalium, "History of Animals") is one of the major texts on biology by the ancient Gr ...
'', on the vestigial eyes of moles, calling them "stunted in development" due to the fact that moles can scarcely see. However, only in recent centuries have anatomical vestiges become a subject of serious study. In 1798,
Étienne Geoffroy Saint-Hilaire Étienne Geoffroy Saint-Hilaire (15 April 177219 June 1844) was a French French (french: français(e), link=no) may refer to: * Something of, from, or related to France France (), officially the French Republic (french: link=no, Républ ...
noted on vestigial structures: His colleague,
Jean-Baptiste Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist Natural history is a domain of inquiry involving organisms, including animals, fu ...

Jean-Baptiste Lamarck
, named a number of vestigial structures in his 1809 book '' Philosophie Zoologique''. Lamarck noted " Olivier's ''
Spalax The genus ''Spalax'' contains the blind, fossorial, or subterranean mole rats, which are one of several types of rodents that are called "mole rats". The Hystricognathi, hystricognath mole-rats of the family Bathyergidae are completely unrelated, ...
'', 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."
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any organic, life, living system that fu ...

Charles Darwin
was 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 ''The Descent of Man, and Selection in Relation to Sex'' is a book by English natural history, naturalist Charles Darwin, first published in 1871, which applies evolutionary theory to human evolution, and details his theory of sexual selection, a ...
'', including the muscles of the ear,
wisdom teeth A third molar, commonly called wisdom tooth, is one of the three molars The molars or molar teeth are large, flat at the back of the . They are more developed in . They are used primarily to during . The name ''molar'' derives from Latin, ...
, the
appendix Appendix may refer to: In documents *Addendum, an addition made to a document by its author after its initial printing or publication *Bibliography, a systematic list of books and other works *Index (publishing), a list of words or phrases with po ...

appendix
, the tail bone,
body hair Body hair, or androgenic hair, is the terminal hair that develops on the human body during and after puberty. It is differentiated from the head hair and less visible vellus hair, which is much finer and lighter in color. The growth of androgenic ...
, and the semilunar fold in the corner of the
eye Eyes are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma Parenchyma () is t ...

eye
. Darwin also noted, in ''
On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life''),The book's full original title was ''On the Origin of Species by Me ...
'', 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.... organ may become rudimentary for its proper purpose, and be used for a distinct object."
Darwin, Charles Charles Robert Darwin (; 12 February 1809 – 19 April 1882) was an English natural history#Before 1900, naturalist, geologist and biologist, best known for his contributions to the science of evolution. His proposition that all speci ...

Darwin, Charles
(1859). '' On the Origin of Species by Means of Natural Selection''. John Murray: London.
In the first edition of ''On the Origin of Species'', Darwin briefly mentioned
inheritance of acquired characters Lamarckism, also known as Lamarckian inheritance or neo-Lamarckism, is the notion that an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies ...
under the heading "''Effects of Use and Disuse''", expressing little doubt that use "strengthens and enlarges certain parts, and disuse diminishes them; and that such modifications are inherited". In later editions he expanded his thoughts on this, and in the final chapter of the 6th edition concluded that species have been modified "chiefly through the natural selection of numerous successive, slight, favorable variations; aided in an important manner by the inherited effects of the use and disuse of parts". In 1893,
Robert Wiedersheim Robert Ernst Eduard Wiedersheim (21 April 1848 in Nürtingen – 12 July 1923 in Schachen ( Lindau)) was a German anatomist Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies l ...
published '' The Structure of Man'', a book on human anatomy and its relevance to man's evolutionary history. ''The Structure of Man'' contained a list of 86 human organs that Wiedersheim described as, "Organs having become wholly or in part functionless, some appearing in the Embryo alone, others present during Life constantly or inconstantly. For the greater part Organs which may be rightly termed Vestigial." Since his time, the function of some of these structures have 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
Horatio Newman Horatio Hackett Newman (March 19, 1875 – August 29, 1957) was an American zoologist and geneticist who taught at the University of Chicago. Along with Frank Rattray Lillie and Charles M. Child, he is credited with building the University of Chicag ...
said in a written statement read into evidence in the
Scopes Trial The Scopes Trial, formally ''The State of Tennessee v. John Thomas Scopes'', and commonly referred to as the Scopes Monkey Trial, was an American legal case from July 10th to July 21st 1925 in which a high school teacher, John T. Scopes, was acc ...

Scopes 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."


Common descent and evolutionary theory

Vestigial structures are often homologous to structures that are functioning normally in other species. Therefore, vestigial structures can be considered evidence for
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolution
, the process by which beneficial heritable traits arise in populations over an extended period of time. The existence of vestigial traits can be attributed to changes in the environment and behavior patterns of the organism in question. Through an examination of these various traits, it is clear that evolution had a hard role in the development of organisms. Every anatomical structure or behavior response has origins in which they were, at one time, useful. As time progressed, the ancient common ancestor organisms did as well. Evolving with time, natural selection played a huge role. More advantageous structures were selected, while others were not. With this expansion, some traits were left to the wayside. As the function of the trait is no longer beneficial for survival, the likelihood that future offspring will inherit the "normal" form of it decreases. In some cases, the structure becomes detrimental to the organism (for example the eyes of a mole can become infected). In many cases the structure is of no direct harm, yet all structures require extra
energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regula ...

energy
in terms of development, maintenance, and weight, and are also a risk in terms of disease (e.g.,
infection An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host A host is a person responsible for guests at an event or for providing hospitality during it. Host may ...

infection
,
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolo ...

cancer
), providing some
selective Selective may refer to: * Selective school, a school that admits students on the basis of some sort of selection criteria ** Selective school (New South Wales) Selective strength: the human body transitions between being weak and strong. This rang ...
pressure for the removal of parts that do not contribute to an organism's fitness. A structure that is not harmful will take longer to be 'phased out' than one that is. However, some vestigial structures may persist due to limitations in development, such that complete loss of the structure could not occur without major alterations of the organism's developmental pattern, and such alterations would likely produce numerous negative side-effects. The toes of many animals such as
horse The horse (''Equus ferus caballus'') is a domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to ...

horse
s, which stand on a single
toe Toes are the Digit (anatomy), digits (fingers) of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being ''digitigrade''. Humans, and other animals that walk on the soles of their feet, are described a ...

toe
, are still evident in a vestigial form and may become evident, although rarely, from time to time in individuals. 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 Common descent is a concept in evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, c ...
with those organisms that have a functional version of the structure.
Douglas Futuyma Douglas Joel Futuyma (born 24 April 1942) is an American evolutionary biologist. He is a Distinguished Professor in the Department of Ecology and Evolution at Stony Brook University in Stony Brook, New York and a Research Associate on staff at the A ...
has stated that vestigial structures make no sense without evolution, just as spelling and usage of many modern
English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventually become the World language, leading lan ...

English
words can only be explained by their
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became ...

Latin
or
Old Norse Old Norse, Old Nordic, or Old Scandinavian is a stage of development of North Germanic dialects before their final divergence into separate Nordic languages. Old Norse was spoken by inhabitants of Scandinavia Scandinavia; : ''Skades ...
antecedents. Vestigial traits can still be considered
adaptation In , adaptation has three related meanings. Firstly, it is the dynamic evolutionary process that fits s to their environment, enhancing their . Secondly, it is a state reached by the population during that process. Thirdly, it is a or adapti ...

adaptation
s. This is because an adaptation is often defined as a trait that has been favored by natural selection. Adaptations, therefore, need not be ''adaptive'', as long as they were at some point.


Examples


Non-human animals

Vestigial characters are present throughout the
animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...

animal
kingdom, and an almost endless list could be given. Darwin said that "it would be impossible to name one of the higher animals in which some part or other is not in a rudimentary condition." The wings of
ostrich ''Struthio'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a ...

ostrich
es,
emu The emu (''Dromaius novaehollandiae'') is the second-largest living bird by height, after its ratite relative, the ostrich. It is endemic Endemism is the state of a species In biology, a species is the basic unit of biological c ...

emu
s, and other
flightless bird Flightless birds are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), ...
s are vestigial; they are remnants of their flying ancestors' wings. The eyes of certain
cavefish Cavefish or cave fish is a generic term for fresh and brackish water fish adapted to life in cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering ...
and
salamander Salamanders are a group of amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most spe ...

salamander
s are vestigial, as they no longer allow the organism to see, and are remnants of their ancestors' functional eyes. Animals that reproduce without sex (via
asexual reproduction Asexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process Biological processes are those processes that are vital for an organism In biology, an organism (from Ancient Gree ...
) generally lose their sexual traits, such as the ability to locate/recognize the opposite sex and copulation behavior. Boas and
pythons The Pythonidae, commonly known as pythons, are a Family (biology), family of Venomous snake, nonvenomous snakes found in Africa, Asia, and Australia. Among its members are some of the largest snakes in the world. Ten Genus, genera and 42 species ...
have vestigial pelvis remnants, which are externally visible as two small
pelvic spur Pelvic spurs are the externally visible portion of the vestigial is a vestigial structure; it has lost much of its ancestral function. Vestigiality is the retention during the process of evolution Evolution is change in the Heredity, heri ...
s on each side of the cloaca. These spurs are sometimes used in copulation, but are not essential, as no colubrid snake (the vast majority of species) possesses these remnants. Furthermore, in most snakes, the left lung is greatly reduced or absent.
Amphisbaenia Amphisbaenia (called amphisbaenians or worm lizards) is a group of usually legless squamate Squamata (, Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin w ...
ns, which independently evolved limblessness, also retain vestiges of the pelvis as well as the pectoral girdle, and have lost their right lung. A case of vestigial organs was described in
polyopisthocotylea Polyopisthocotylea is a subclass of parasitic flatworms in the class Monogenea. WoRMS (2019). Polyopisthocotylea. Accessed at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=119220 on 2019-02-08Yamaguti, S. (1963). Systema Helminthum Volum ...
n
Monogenea Monogeneans are a group of ectoparasitic flatworm The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλά ...

Monogenea
ns (
parasitic Parasitism is a Symbiosis, symbiotic biological interactions, relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is adaptation (biology), ad ...
flatworm The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a count ...

flatworm
s). These parasites usually have a posterior attachment organ with several clamps, which are sclerotised organs attaching the worm to the gill of the
host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places *Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman *Michel Host (19 ...
fish. These clamps are extremely important for the survival of the parasite. In the family Protomicrocotylidae, species have either normal clamps, simplified clamps, or no clamps at all (in the genus '' Lethacotyle''). After a comparative study of the relative surface of clamps in more than 100
Monogenea Monogeneans are a group of ectoparasitic flatworm The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλά ...

Monogenea
ns, this has been interpreted as an evolutionary sequence leading to the loss of clamps. Coincidentally, other attachment structures (lateral flaps, transverse striations) have evolved in protomicrocotylids. Therefore, clamps in protomicrocotylids were considered vestigial organs. In the foregoing examples the vestigiality is generally the (sometimes incidental) result of
adaptive evolution In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process that fits organisms to their environment, enhancing their Fitness (biology), evolutionary fitness. Secondly, it is a state reached by the popula ...

adaptive evolution
. However, there are many examples of vestigiality as the product of drastic
mutation In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechan ...
, and such vestigiality is usually harmful or counter-adaptive. One of the earliest documented examples was that of vestigial wings in ''
Drosophila ''Drosophila'' () is a genus of fly, flies, belonging to the family (biology), family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the character ...

Drosophila
''. Many examples in many other contexts have emerged since.Snustad, D. Peter. & Simmons, Michael J. Principles of Genetics. Publisher: Wiley, 2008.


Humans

Human vestigiality is related to
human evolution Human evolution is the evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual ...

human evolution
, and includes a variety of characters occurring in the
human Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A speci ...

human
species. Many examples of these are vestigial in other
primate A primate ( ) (from Latin , from 'prime, first rank') is a eutherian mammal constituting the Taxonomy (biology), taxonomic order (biology), order Primates (). Primates arose 85–55 million years ago first from small Terrestrial animal, ...

primate
s and related animals, whereas other examples are still highly developed. The human
caecum The cecum or caecum is a pouch within the peritoneum The peritoneum is the serous membrane In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and liv ...
is vestigial, as often is the case in
omnivore An omnivore () is an animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Over 1.5 million animal have been — ...
s, being reduced to a single chamber receiving the content of the
ileum The ileum () is the final section of the small intestine The small intestine or small bowel is an organ (anatomy), organ in the human gastrointestinal tract, gastrointestinal tract where most of the #Absorption, absorption of nutrients from f ...
into the
colon Colon commonly refers to: * Colon (punctuation) (:), a punctuation mark * Major part of large intestine, the final section of the digestive system Colon may also refer to: Places * Colon, Michigan, US * Colon, Nebraska, US * Kowloon, Hong Kong, s ...

colon
. The ancestral caecum would have been a large, blind diverticulum in which resistant plant material such as
cellulose Cellulose is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...

cellulose
would have been fermented in preparation for absorption in the colon.
Darwin, Charles Charles Robert Darwin (; 12 February 1809 – 19 April 1882) was an English natural history#Before 1900, naturalist, geologist and biologist, best known for his contributions to the science of evolution. His proposition that all speci ...

Darwin, Charles
(1871). ''
The Descent of Man, and Selection in Relation to Sex ''The Descent of Man, and Selection in Relation to Sex'' is a book by English naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any organic, life, living system that functions as ...
''. John Murray: London.
Analogous organs in other animals similar to humans continue to perform similar functions. The
coccyx The coccyx (plural: ''coccyges'' or ''coccyxes''), commonly referred to as the tailbone, is the final segment of the vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton Axial may refer ...
, or tailbone, though a vestige of the tail of some primate ancestors, is functional as an anchor for certain pelvic muscles including: the levator ani muscle and the largest gluteal muscle, the gluteus maximus. Other structures that are vestigial include the plica semilunaris on the inside corner of the
eye Eyes are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma Parenchyma () is t ...

eye
(a remnant of the
nictitating membrane The nictitating membrane (from Latin '' nictare'', to blink) is a transparent or translucent In the field of optics Optics is the branch of physics Physics is the that studies , its , its and behavior through , and the related e ...
); and (as seen at right)
muscles Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly cat ...
in the
ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear The outer ear, external ear, or auris externa is the external part of the ear, which consists ...

ear
. Other organic structures (such as the
occipitofrontalis muscle The occipitofrontalis muscle (epicranius muscle) is a skeletal muscle, muscle which covers parts of the human skull, skull. It consists of two parts or bellies: The Occipitalis muscle, occipital belly, near the occipital bone, and the Frontalis musc ...
) have lost their original functions (to keep the head from falling) but are still useful for other purposes (facial expression). Humans also bear some vestigial behaviors and reflexes. The formation of
goose bumps Goose bumps, goosebumps or goose-pimples are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is tickled, cold , a common physiological response to cold, aiming to reduce the loss of bo ...

goose bumps
in humans under stress is a vestigial
reflex In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
; its function in human ancestors was to raise the body's hair, making the ancestor appear larger and scaring off predators. The ''arrector pili'' (muscle that connects the hair follicle to connective tissue) contracts and creates goosebumps on skin. 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 a gene that is functional in most other mammals and which produces L-gulonolactone oxidase, an
enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates in ...

enzyme
that can make
vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a vitamin A vitamin is an organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain ca ...

vitamin C
. A documented mutation deactivated the gene in an ancestor of the modern infraorder of , and it now remains in their
genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

genome
s, including the
human genome The human genome is a complete set of nucleic acid sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecules c ...

human genome
, as a vestigial sequence called a
pseudogene Pseudogenes are nonfunctional segments of DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon ...
. The shift in human diet towards soft and processed food over time caused a reduction in the number of powerful grinding teeth, especially the third molars or wisdom teeth, which were highly prone to impaction.


Plants and fungi

Plants also have vestigial parts, including functionless
stipulesIn botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient ...
and
carpels '' stigmas and style Gynoecium (, from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided in ...

carpels
, leaf reduction of
Equisetum ''Equisetum'' (; horsetail, snake grass, puzzlegrass) is the only living genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study ...

Equisetum
, paraphyses of
Fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

Fungi
. Well known examples are the reductions in floral display, leading to smaller and/or paler flowers, in plants that reproduce without
outcrossing Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing unrelated genetic material into a breeding line. It increases genetic diversity Genetic diversity is the total number of gen ...
, for example via
selfing Selfing or self-fertilization is the union of male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot sexual re ...
or obligate clonal reproduction.CG Eckert (2002
The loss of sex in clonal plants
Evolutionary Ecology 45:501-520


See also

*
Atavism In biology, an atavism is a modification of a biological structure whereby an ancestral genetic Trait (biological), trait reappears after having been lost through evolutionary change in previous generations. Atavisms can occur in several ways; one ...
*
Dewclaw A dewclaw is a Digit (anatomy), digit – Vestigial structure, vestigial in some animals – on the foot of many mammals, birds, and reptiles (including some extinct orders, like certain theropods). It commonly grows higher on the leg than the ...
*
Exaptation Exaptation and the related term co-option Co-option (also co-optation, sometimes spelt coöption or coöptation) has two common meanings. It may refer to the process of adding members to an elite group A group is a number A number is a mat ...
*
Human vestigiality In the context of human evolution Human evolution is the evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to thei ...
*
Maladaptation A maladaptation () is a trait Trait may refer to: * Phenotypic trait in biology, which involve genes and characteristics of organisms * Trait (computer programming), a model for structuring object-oriented programs (a template class in the C++ p ...
*
Plantaris muscle The plantaris is one of the superficial muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ sys ...
* Recessive refuge * Spandrel (biology) *Vestigial response


References


External links


Vestigial organs
at the TalkOrigins Archive {{evolution Evolutionary biology concepts