digplanet beta 1: Athena
Share digplanet:

Agriculture

Applied sciences

Arts

Belief

Business

Chronology

Culture

Education

Environment

Geography

Health

History

Humanities

Language

Law

Life

Mathematics

Nature

People

Politics

Science

Society

Technology

Exaptation (a replacement for the teleologically-loaded term "pre-adaptation"[1]) 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 in both anatomy and behaviour. Bird feathers are a classic example: initially they may have evolved for temperature regulation, but later were adapted for flight. Interest in exaptation relates to both the process and products of evolution: the process that creates complex traits and the products (functions, anatomical structures, biochemicals, etc.) that may be imperfectly developed.[2][3]

History and definitions[edit]

The idea that the function of a trait might shift during its evolutionary history originated with Charles Darwin (Darwin 1859). For many years the phenomenon was labeled "preadaptation", but since this term suggests teleology, which is contrary to a basic principle of natural selection, it has been replaced by the term exaptation.

The idea had been explored by several scholars[4] when in 1982 Gould and Vrba introduced the term "exaptation". However, this definition had two categories with different implications for the role of adaptation.

(1) A character, previously shaped by natural selection for a particular function (an adaptation), is coopted for a new use—cooptation. (2) A character whose origin cannot be ascribed to the direct action of natural selection (a nonaptation), is coopted for a current use—cooptation. (Gould and Vrba 1982, Table 1)

The definitions are silent as to whether exaptations had been shaped by natural selection after cooption, although Gould and Vrba cite examples (e.g., feathers) of traits shaped after cooption. Note that the selection pressure upon a trait is likely to change if it is (especially, primarily or solely) used for a new purpose, potentially initiating a different evolutionary trajectory.

To avoid these ambiguities, Buss, et al. (1998) suggested the term "co-opted adaptation", which is limited to traits that evolved after cooption. However, the commonly used terms of "exaptation" and "cooption" are ambiguous in this regard.

Preadaptation[edit]

In some circumstances, the "pre-" in preadaptation can be interpreted as applying, for non-teleological reasons, prior to the adaptation itself, creating a meaning for the term that is distinct from exaptation.[5][6] For example, future environments (say, hotter or drier ones), may resemble those already encountered by a population at one of its current spatial or temporal margins.[5] This is not actual foresight, but rather the luck of having adapted to a climate which later becomes more prominent. Cryptic genetic variation may have the most strongly deleterious mutations purged from it, leaving an increased chance of useful adaptations,[6][7] but this represents selection acting on current genomes with consequences for the future, rather than foresight.

Examples[edit]

There are many examples of exaptations. A classic example is how feathers, which initially evolved for heat regulation, were co-opted for display, and later co-opted for use in bird flight. Another example is the lungs of many basal fish, which evolved into the lungs of terrestrial vertebrates but also underwent exaptation to become the gas bladder, a buoyancy control organ, in derived fish.[8]

A behavioural example pertains to subdominant wolves licking the mouths of alpha wolves as a sign of submissiveness. (Similarly, dogs, which are wolves who through a long process were domesticated, lick the faces of their human owners.) This trait can be explained as an exaptation of wolf pups licking the faces of adults to encourage them to regurgitate food.[9]

Arthropods provide the earliest identifiable fossils of land animals, from about 419 million years ago in the Late Silurian, and terrestrial tracks from about 450 million years ago appear to have been made by arthropods.[10] Arthropods were well pre-adapted to colonize land, because their existing jointed exoskeletons provided support against gravity and mechanical components that could interact to provide levers, columns and other means of locomotion that did not depend on submergence in water.[11]

Implications[edit]

Evolution of complex traits[edit]

One of the challenges to Darwin's theory of evolution was explaining how complex structures could evolve gradually,[12] given that their incipient forms may have been inadequate to serve any function. As Mivart (a critic of Darwin) pointed out, 5 percent of a bird wing would not be functional. The incipient form of complex traits would not have survived long enough to evolve to a useful form.

As Darwin elaborated in the last edition of The Origin of Species,[13] many complex traits evolved from earlier traits that had served different functions. By trapping air, primitive wings would have enabled birds to efficiently regulate their temperature, in part, by lifting up their feathers when too warm. Individual animals with more of this functionality would more successfully survive and reproduce, resulting in the proliferation and intensification of the trait.

Eventually, feathers became sufficiently large to enable some individuals to glide. These individuals would in turn more successfully survive and reproduce, resulting in the spread of this trait because it served a second and still more beneficial function: that of locomotion. Hence, the evolution of bird wings can be explained by a shifting in function from the regulation of temperature to flight.

Jury-rigged design[edit]

Darwin explained how the traits of living organisms are well-designed for their environment, but he also recognized that many traits are imperfectly designed. They appear to have been made from available material, that is, jury-rigged.[14] Understanding exaptations may suggest hypotheses regarding subtleties in the adaptation. For instance, that feathers evolved initially for thermal regulation may help to explain some of their features unrelated to flight (Buss et al., 1998). However, this is readily explained by the fact that they serve a dual purpose.

Some of the chemical pathways for physical pain and pain from social exclusion overlap (MacDonald and Leary, 2005). The physical pain system may have been co-opted to motivate social animals to respond to threats to their inclusion in the group.

See also[edit]

Notes[edit]

  1. ^ Gould, S. J.; Vrba, E. S. (1982). "Exaptation - a missing term in the science of form". Paleobiology 8 (1): 4–15. JSTOR 2400563.  edit
  2. ^ Bock, W.J. (1959). "Preadaptation and multiple evolutionary pathways". Evolution 13 (2): 194–211. doi:10.2307/2405873. JSTOR 2405873. 
  3. ^ Hayden, Eric J.; Evandro Ferrada, Andreas Wagner (2 June 2011). "Cryptic genetic variation promotes rapid evolutionary adaptation in an RNA enzyme". Nature 474 (7349): 92–95. doi:10.1038/nature10083. PMID 21637259. 
  4. ^ See Jacob (1977) and Mayr (1982) for references.
  5. ^ a b Eshel,I. Matessi, C. (1998). "Canalization, genetic assimilation and preadaptation: A quantitative genetic model". Genetics 4: 2119–2133. 
  6. ^ a b Masel, Joanna (March 2006). "Cryptic Genetic Variation Is Enriched for Potential Adaptations". Genetics (Genetics Society of America) 172 (3): 1985–1991. doi:10.1534/genetics.105.051649. PMC 1456269. PMID 16387877. 
  7. ^ Rajon, E., Masel, J. (2011). "Evolution of molecular error rates and the consequences for evolvability". PNAS 108 (3): 1082–1087. doi:10.1073/pnas.1012918108. PMC 3024668. PMID 21199946. 
  8. ^ Colleen Farmer (1997). "Did Lungs and the Intracardiac Shunt Evolve to Oxygenate the Heart in Vertebrates?". Paleobiology (Paleontological Society) 23 (3): 358–372. JSTOR 2401109. 
  9. ^ "accessed May 16, 2008". Wolf.org. Retrieved 2013-12-17. 
  10. ^ Pisani, D., Laura L Poling, L.L., Lyons-Weiler M., and Hedges, S.B. (2004). "The colonization of land by animals: molecular phylogeny and divergence times among arthropods". BMC Biology 2: 1. doi:10.1186/1741-7007-2-1. PMC 333434. PMID 14731304. 
  11. ^ Cowen, R. History of Life (3rd ed.). Blackwell Science. p. 126. ISBN 0-632-04444-6. 
  12. ^ The development of complex structures (i.e., evolution of novelties) occur either by intensification of an existing function or by a switch in functions.
  13. ^ Darwin 1872
  14. ^ Jacob (1977) sees much of evolution as "tinkering," that is, working with available traits. "Tinkering" includes (but is not limited to) shifts in function.

References[edit]

External links[edit]


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Exaptation — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.

13 news items

 
Bloody Elbow
Fri, 25 Jul 2014 06:52:30 -0700

April 2001: Less than a month after his 19th birthday, Robbie Lawler has his mixed martial arts pro debut. He knocks out John Reed at Extreme Challenge 39 in Illinois in one round. He goes to train at Miletich Fighting Systems, the greatest camp in the ...

Chronicle of Higher Education (subscription)

Chronicle of Higher Education (subscription)
Sun, 27 Jul 2014 21:07:53 -0700

Ever since Stephen Jay Gould and Elisabeth Vrba introduced the concept of exaptation—a trait evolving to serve one function but then taking on another—we have had a way of describing the emergence of things like altruism and morality from humbler ...
 
Discover Magazine (blog)
Wed, 02 Jul 2014 10:01:34 -0700

Researchers took their exaptation theory one step further by suggesting not just feathers, but also forelimb anatomy and other physiological traits, evolved in therapod dinosaurs for non-flight-related functions. This selection likely happened ...

Motherboard

Motherboard
Sun, 06 Jul 2014 10:03:45 -0700

“Pennaceous feathers thus represented an exaptation and were later, in several lineages and following different patterns, recruited for aerodynamic functions," they continued. "This indicates that the origin of flight in avialans was more complex than ...

University Herald

University Herald
Wed, 02 Jul 2014 13:26:15 -0700

Red Kangaroos (Photo : Flickr/CC) Red Kangaroos use the tail to help propel themselves forward during grazing. Kangaroos may have four limbs, two of which being powerful hind legs used for hopping, but new research suggests they use their tail as a ...
 
科学时报 (博客)
Tue, 22 Jul 2014 04:52:45 -0700

研究表明,科学和技术创新基于人们已经把握的科技成就积累,具有“邻近可能性”(Adjacent Possible)和“扩展适应性”(Exaptation)。也就是说,一项崭新的科学和技术首创,需要基于本地的科技水准,包括原创科技累积和从其 ...

Tagesspiegel

Tagesspiegel
Thu, 03 Jul 2014 03:48:10 -0700

Die spätere „Zweckentfremdung“ der Federn zum Fliegen ist ein Beispiel für „Exaptation“. Dieser von dem Paläontologen Stephen Jay Gould geprägte Ausdruck bezeichnet das Phänomen, dass bestimmte Merkmale (wie Federn) plötzlich neben ihrem ...

AFIS science

AFIS science
Wed, 09 Jul 2014 11:22:30 -0700

L'utilisation du raisonnement dans le domaine scientifique peut être vue sous cet angle comme une exaptation (l'utilisation d'une fonction initialement sélectionnée par l'évolution pour de tout autres motifs). La psychologie évolutionniste a aussi son ...
Loading

Oops, we seem to be having trouble contacting Twitter

Talk About Exaptation

You can talk about Exaptation with people all over the world in our discussions.

Support Wikipedia

A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia. Please add your support for Wikipedia!