Vestigiality is the retention, during the process of
evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
, 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 and may refer to:
Mathematics and science
* Positive formula, a logical formula not containing negation
* Positive number, a number that is greater than 0
* Plus sign, the sign "+" used to indicate a posi ...
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 ...
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) in various tetrapods. ...
; and the hindlimbs of the
snake
Snakes are elongated, Limbless vertebrate, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Ma ...
and
whale
Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...
.
Overview
![Darwin-s-tubercle](https://upload.wikimedia.org/wikipedia/commons/2/29/Darwin-s-tubercle.jpg)
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 an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...
to late adulthood.
![Rudimentary hindlegs spurs in Boa constrictor snake](https://upload.wikimedia.org/wikipedia/commons/2/20/Rudimentary_hindlegs_spurs_in_Boa_constrictor_snake.jpg)
Vestigiality, biologically speaking, refers to organisms retaining organs that have seemingly lost their original function. 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 develops in the embryo. The cecum is a pouch-like structure of the large i ...
, vestigial in the sense of retaining no significant digestive function.
Similar concepts apply at the molecular level—some
nucleic acid
Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main cl ...
sequences in
eukaryotic
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
genomes
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding gen ...
have no known biological function; some of them may be "
junk DNA
Non-coding DNA (ncDNA) sequences are components of an organism's DNA that do not genetic code, encode protein sequences. Some non-coding DNA is Transcription (genetics), transcribed into functional non-coding RNA molecules (e.g. transfer RNA, micro ...
", 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 (ncDNA) sequences are components of an organism's DNA that do not encode protein sequences. Some non-coding DNA is transcribed into functional non-coding RNA molecules (e.g. transfer RNA, microRNA, piRNA, ribosomal RNA, and regul ...
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
pseudogene
Pseudogenes are nonfunctional segments of DNA that resemble functional genes. Most arise as superfluous copies of functional genes, either directly by DNA duplication or indirectly by Reverse transcriptase, reverse transcription of an mRNA trans ...
s 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
In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a f ...
. Such vestigial structures typically are degenerate, atrophied, or rudimentary, and tend to be much more
variable
Variable may refer to:
* Variable (computer science), a symbolic name associated with a value and whose associated value may be changed
* Variable (mathematics), a symbol that represents a quantity in a mathematical expression, as used in many ...
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 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. Exaptations are common ...
. 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 List of Sphenisciformes by population, Sphenisciformes , family (biology), family Spheniscidae ) are a group of Water bird, aquatic flightless birds. They live almost exclusively in the Southern Hemisphere: on ...
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-tallest living bird after its ratite relative the ostrich. It is endemic to Australia where it is the largest native bird and the only extant member of the genus ''Dromaius''. The 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
Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There are ...
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, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance.
Genetic drift may cause gene variants to disappear completely and there ...
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 of biological evolution developed by the English naturalist Charles Darwin (1809–1882) and others, stating that all species of organisms arise and develop through the natural selection of small, inherited variations that ...
provided a widely accepted explanation. In the 4th century BC,
Aristotle
Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
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 naturalist who established the principle of "unity of composition". He was a colleague of Jean-Baptiste Lamarck and expanded and defended Lamarck's evolutionary theories. ...
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, biologist, academic, and soldier. He was an early proponent of the idea that biologi ...
, named a number of vestigial structures in his 1809 book ''
Philosophie Zoologique
''Philosophie zoologique'' ("Zoological Philosophy, or Exposition with Regard to the Natural History of Animals") is an 1809 book by the French naturalist Jean-Baptiste Lamarck, in which he outlines his pre-Darwinian theory of evolution, part of ...
''. Lamarck noted "
Olivier
Olivier is the French form of the given name Oliver. It may refer to:
* Olivier (given name), a list of people and fictional characters
* Olivier (surname), a list of people
* Château Olivier, a Bordeaux winery
*Olivier, Louisiana, a rural popul ...
's ''
Spalax
''Spalax'' is a genus of rodent in the family Spalacidae, subfamily '' Spalacinae'' (blind mole-rats). It is one of two extant genera in the subfamily Spalacinae, alongside ''Nannospalax''.'
Species in this genus are found in eastern Europe ...
'', 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, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
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 naturalist Charles Darwin, first published in 1871, which applies evolutionary theory to human evolution, and details his theory of sexual selection, a form of biolo ...
'', including the
muscles of the ear,
wisdom teeth
A third molar, commonly called wisdom tooth, is one of the three molars per quadrant of the human dentition. It is the most posterior of the three. The age at which wisdom teeth come through ( erupt) is variable, but this generally occurs betw ...
, the
appendix, the
tail bone
The coccyx (plural, : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horse anatomy, horses. In tailless primates ( ...
,
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 androge ...
, and the
semilunar fold in the corner of the
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 naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
(1859). ''On the Origin of Species by Means of Natural Selection
On, on, or ON may refer to:
Arts and entertainment Music
* On (band), a solo project of Ken Andrews
* ''On'' (EP), a 1993 EP by Aphex Twin
* ''On'' (Echobelly album), 1995
* ''On'' (Gary Glitter album), 2001
* ''On'' (Imperial Teen album), 200 ...
''. 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 can pass on to its offspring physical characteristics that the parent organism acquired through use or disuse during its lifetime. It is also calle ...
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 who is famous for publishing a list of 86 "vestigial organs" in his book ''The Structure of Man: An Index to His Past Histor ...
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 Ch ...
said in a written statement read into evidence in the
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 characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
, 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, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
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 tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
,
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 tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
), providing some
selective 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, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...
s, which stand on a single
toe
Toes are the 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 as being ''plan ...
, 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 applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the last universal comm ...
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 ...
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 people
English may also refer to:
Peoples, culture, and language
* ''English'', an adjective for something of, from, or related to England
** English national ide ...
words can only be explained by their
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
or
Old Norse
Old Norse, Old Nordic, or Old Scandinavian, is a stage of development of North Germanic languages, North Germanic dialects before their final divergence into separate Nordic languages. Old Norse was spoken by inhabitants of Scandinavia and t ...
antecedents.
Vestigial traits can still be considered
adaptation
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
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 are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
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
Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There are ...
es,
emu
The emu () (''Dromaius novaehollandiae'') is the second-tallest living bird after its ratite relative the ostrich. It is endemic to Australia where it is the largest native bird and the only extant member of the genus ''Dromaius''. The emu' ...
s and other
flightless bird
Flightless birds are birds that through evolution lost the ability to fly. There are over 60 extant species, including the well known ratites (ostriches, emu, cassowaries, rheas, and kiwi) and penguins. The smallest flightless bird is the In ...
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 caves and other underground habitats. Related terms are subterranean fish, troglomorphic fish, troglobitic fish, stygobitic fish, phreatic fish and hypog ...
and
salamander
Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
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 that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...
) 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 of nonvenomous snakes found in Africa, Asia, and Australia. Among its members are some of the largest snakes in the world. Ten genera and 42 species are currently recognized.
Distribution ...
have vestigial pelvis remnants, which are externally visible as two small
pelvic spur
Pelvic spurs are the externally visible portion of the vestigial remnants of legs found on each side of the cloaca in primitive snakes, such as boas and pythons. The remnants of a pelvis and femur, which have no connection with the spine, simply " ...
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 squamates, comprising over 200 extant species. Amphisbaenians are characterized by their long bodies, the reduction or loss of the limbs, and rudimentary eyes. As ...
ns, which independently evolved limblessness, also retain vestiges of the pelvis as well as the pectoral girdle, and have lost their right lung.
![Journal](https://upload.wikimedia.org/wikipedia/commons/6/66/Journal.pone.0079155.g003_Clamps_in_various_genera_of_Protomicrocotylidae.png)
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 flatworms commonly found on the skin, gills, or fins of fish. They have a direct lifecycle and do not require an intermediate host. Adults are hermaphrodites, meaning they have both male and female reprod ...
ns (
parasitic
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
flatworm
The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegment ...
s). These parasites usually have a posterior attachment organ with several
clamps
Clamp may refer to:
Tools and devices
*Brick clamp, an early method of baking bricks
*Clamp (tool), a device or tool used to hold objects in a fixed relative position (many types listed)
** C-clamp
** C-clamp (stagecraft)
**Riser clamp, a device ...
, 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 ...
fish. These clamps are extremely important for the survival of the parasite. In the family
Protomicrocotylidae
Protomicrocotylidae is a family of monogenean parasites in the order Mazocraeidea.
The type-genus of the family is ''Protomicrocotyle''. The genus was created in 1922 by Thomas Harvey Johnston and Oscar Werner Tiegs for a worm previously des ...
, species have either normal clamps, simplified clamps, or no clamps at all (in the genus ''
Lethacotyle
''Lethacotyle'' is a genus of polyopisthocotylean monogeneans, included in the family Protomicrocotylidae.
The genus includes only two species: ''Lethacotyle fijiensis'' Manter & Price, 1953
Manter, H. W. & Price, D. F. 1953: Some Monogenetic Tre ...
''). After a comparative study of the relative surface of clamps in more than 100
Monogenea
Monogeneans are a group of ectoparasitic flatworms commonly found on the skin, gills, or fins of fish. They have a direct lifecycle and do not require an intermediate host. Adults are hermaphrodites, meaning they have both male and female reprod ...
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
Clamp may refer to:
Tools and devices
*Brick clamp, an early method of baking bricks
*Clamp (tool), a device or tool used to hold objects in a fixed relative position (many types listed)
** C-clamp
** C-clamp (stagecraft)
**Riser clamp, a device ...
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 of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...
. However, there are many examples of vestigiality as the product of drastic
mutation
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mi ...
, 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 flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species ...
''. 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 evolutionary process within the history of primates that led to the emergence of ''Homo sapiens'' as a distinct species of the hominid family, which includes the great apes. This process involved the gradual development of ...
, and includes a variety of characters occurring in the
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
species. Many examples of these are vestigial in other
primate
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...
s and related animals, whereas other examples are still highly developed. The human
caecum
The cecum or caecum is a pouch within the peritoneum that is considered to be the beginning of the large intestine. It is typically located on the right side of the body (the same side of the body as the appendix, to which it is joined). The wo ...
is vestigial, as often is the case in
omnivore
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutr ...
s, being reduced to a single chamber receiving the content of the
ileum
The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine ma ...
into the
colon. The ancestral caecum would have been a large, blind diverticulum in which resistant plant material such as
cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...
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 naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
(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 Charles Darwin, first published in 1871, which applies evolutionary theory to human evolution, and details his theory of sexual selection, a form of biolo ...
''. John Murray: London. Analogous organs in other animals similar to humans continue to perform similar functions. The
coccyx
The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and othe ...
, 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 (a remnant of the
nictitating membrane
The nictitating membrane (from Latin '' nictare'', to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision. All ...
);
and (as seen at right)
muscles
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...
in the
ear
An ear is the organ that enables hearing and, in mammals, body balance using the vestibular system. In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. The outer ear consists of ...
.
Other organic structures (such as the
occipitofrontalis muscle
The occipitofrontalis muscle (epicranius muscle) is a muscle which covers parts of the skull. It consists of two parts or bellies: the occipital belly, near the occipital bone, and the frontal belly, near the frontal bone. It is supplied by th ...
) 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 or experiencing strong emotions such as fear, euphoria or sexual arousal.
The fo ...
in humans under
stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
is a vestigial
reflex
In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus.
Reflexes are found with varying levels of complexity in organisms with a nervous system. A reflex occurs ...
; 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
L-Gulonolactone oxidase ( ECbr>1.1.3.8 is an enzyme that produces vitamin C, but is non-functional in Haplorrhini (including humans), in some bats, and in guinea pigs. It catalyzes the reaction of L-gulono-1,4-lactone with oxygen to form L-xyl ...
, an
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
that can make
vitamin C
Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) an ...
. A documented mutation deactivated the gene in an ancestor of the modern infraorder of
monkeys, and apes, and it now remains in their
genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
s, including the
human genome
The human genome is a complete set of nucleic acid sequences for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. These are usually treated separately as the n ...
, as a vestigial sequence called a
pseudogene
Pseudogenes are nonfunctional segments of DNA that resemble functional genes. Most arise as superfluous copies of functional genes, either directly by DNA duplication or indirectly by Reverse transcriptase, reverse transcription of an mRNA trans ...
.
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
stipules
In botany, a stipule is an outgrowth typically borne on both sides (sometimes on just one side) of the base of a leafstalk (the petiole). Stipules are considered part of the anatomy of the leaf of a typical flowering plant, although in many speci ...
and
carpels
Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) ''pistils'' ...
, leaf reduction of
Equisetum
''Equisetum'' (; horsetail, snake grass, puzzlegrass) is the only living genus in Equisetaceae, a family of ferns, which reproduce by spores rather than seeds.
''Equisetum'' is a "living fossil", the only living genus of the entire subclass Eq ...
,
paraphyses of
Fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
. 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 distantly related genetic material into a breeding line, thereby increasing genetic diversity.
Outcrossing can be a useful ...
, for example via
selfing
Autogamy, or self-fertilization, refers to the fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a reproductive mechanism employed by many flowering plants. However, species o ...
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 reappears after having been lost through evolutionary change in previous generations. Atavisms can occur in several ways; one of which is when ...
*
Dewclaw
A dewclaw is a digit – 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 rest of the foot, such that in digit ...
*
Exaptation
Exaptation and the related term 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. Exaptations are common ...
*
Human vestigiality
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, an ...
*
Maladaptation
In evolution, a maladaptation () is a trait that is (or has become) more harmful than helpful, in contrast with an adaptation, which is more helpful than harmful. All organisms, from bacteria to humans, display maladaptive and adaptive traits. I ...
*
Plantaris muscle
The plantaris is one of the superficial muscles of the superficial posterior compartment of the leg, one of the fascial compartments of the leg.
It is composed of a thin muscle belly and a long thin tendon. While not as thick as the achilles te ...
*
Recessive refuge
In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The first ...
*
Spandrel (biology)
In evolutionary biology, a spandrel is a phenotypic trait that is a byproduct of the evolution of some other characteristic, rather than a direct product of adaptive selection. Stephen Jay Gould and Richard Lewontin brought the term into biology ...
*
Vestigial response
References
External links
Vestigial organsat the
TalkOrigins Archive
The TalkOrigins Archive is a website that presents mainstream science perspectives on the antievolution claims of young-earth, old-earth, and "intelligent design" creationists. With sections on evolution, creationism, geology, astronomy and homi ...
{{evolution
Evolutionary biology concepts