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Encyclopedia > Punctuated equilibrium

Punctuated equilibrium (or punctuated equilibria) is a theory in evolutionary biology which states that most sexually reproducing species will show little to no evolutionary change throughout their history. When evolution does occur, it happens sporadically (by splitting) and occurs relatively quickly compared to the species' full duration on earth. For this reason, the theory is sometimes called evolution by jerks. (Ghiselin, 1986) Punctuated equilibrium is commonly contrasted against the theory of phyletic gradualism (“evolution by creeps”), which hypothesizes that most evolution occurs uniformly and by the steady and gradual transformation of whole lineages (anagenesis). For a non-technical introduction to the topic, please see Introduction to evolution. ... Sexual reproduction is a type of reproduction that results in increasing genetic diversity of the offspring. ... Charles Darwins first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837) Speciation is the evolutionary process by which new biological species arise. ... In biology, a species is one of the basic units of biodiversity. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... Phyletic gradualism is a macroevolutionary hypothesis rooted in uniformitarianism. ... Anagenesis is the progressive evolution of species involving a change in gene frequency in an entire population rather than a cladogenetic branching event. ...

Contents

Punctuated equilibrium's history

Punctuated equilibrium originated as an extension of Ernst Mayr's concept of genetic revolutions by peripatric and allopatric speciation. Although the workings of the theory were proposed and specifically identified by Mayr in 1954, most historians of science recognize Niles Eldredge and Stephen Jay Gould's 1972 paper as the principal source of its acceptance (by both paleontologists and evolutionary biologists) and as the foundational document of a new and serious paleontological research program (Mayr 1992: 25-26, Shermer 2001: 102-113). Punctuated equilibrium differed from Mayr simply in that Eldredge and Gould had placed considerably greater emphasis on stasis, whereas Mayr was generally concerned with explaining the morphological discontinuity (or punctuational patterns) found in the fossil record. This article has been identified as possibly containing errors. ... Peripatric speciation (also known as Parapatry) is a type of speciation in the theory of natural selection. ... Allopatric speciation, also known as geographic speciation, occurs when populations physically isolated by an extrinsic barrier evolve intrinsic (genetic) reproductive isolation such that if the barrier between the populations breaks down, individuals of the two populations can no longer interbreed. ... Year 1954 (MCMLIV) was a common year starting on Friday of the Gregorian calendar. ... Science is a body of empirical and theoretical knowledge, produced by a global community of researchers, making use of specific techniques for the observation and explanation of real phenomena, this techne summed up under the banner of scientific method. ... Dr. Niles Eldredge (born August 25, 1943) is an American paleontologist, who, along with Stephen Jay Gould, proposed the theory of punctuated equilibrium in 1972. ... It has been suggested that Darwinian Fundamentalism be merged into this article or section. ... 1972 (MCMLXXII) was a leap year starting on Saturday. ... Paleontology or palaeontology (see Spelling differences) is the study of the history and development of life on Earth, including that of ancient plants and animals, based on the fossil record (evidence of their prehistoric existence as typically preserved in sedimentary rocks). ... Evolutionary biology is a subfield of biology concerned with the origin and descent of species, as well as their change, multiplication, and diversity over time. ... This article has been identified as possibly containing errors. ... Michael Shermer Michael Shermer Ph. ... Dr. Niles Eldredge (born August 25, 1943) is an American paleontologist, who, along with Stephen Jay Gould, proposed the theory of punctuated equilibrium in 1972. ... It has been suggested that Darwinian Fundamentalism be merged into this article or section. ...


The Eldredge and Gould paper was presented at the Annual Meeting of the Geological Society of America in 1971.(Eldredge and Gould 1972, Gould 1991) The symposium focused its attention on how modern microevolutionary studies could revitalize various aspects of paleontology and macroevolution. Tom Schopf, who organized that year's meeting, assigned Stephen Jay Gould the topic of speciation. Gould recalls that "Eldredge's 1971 publication [on Paleozoic trilobites] had presented the only new and interesting ideas on the paleontological implications of the subject—so I asked Schopf if we could present the paper jointly." (Gould 2002: 775) They did. According to Gould "the ideas came mostly from Niles, with yours truly acting as a sounding board and eventual scribe. I coined the term punctuated equilibrium and wrote most of our 1972 paper, but Niles is the proper first author in our pairing of Eldredge and Gould." (Gould 1991) The Geological Society of America (or GSA) is a nonprofit organization dedicated to the advancement of the geosciences. ... 1971 (MCMLXXI) was a common year starting on Friday (the link is to a full 1971 calendar). ... Microevolution is the occurrence of small-scale changes in allele frequencies in a population, over a few generations, also known as change at or below the species level. ... 1971 (MCMLXXI) was a common year starting on Friday (the link is to a full 1971 calendar). ... The Paleozoic Era (from the Greek palaio, old and zoion, animals, meaning ancient life) is the earliest of three geologic eras of the Phanerozoic eon. ... Orders Agnostida Redlichiida Corynexochida Lichida Phacopida Proetida Asaphida Harpetida Ptychopariida Nektaspida (doubtful order) Trilobites are extinct arthropods in the class Trilobita. ... For album titles with the same name, see 2002 (album). ... 1972 (MCMLXXII) was a leap year starting on Saturday. ... 1991 (MCMXCI) was a common year starting on Tuesday of the Gregorian calendar. ...


Tempo and mode

Ernst Mayr's paper "Change of genetic environment and evolution" (1954) emphasized the homogenizing effects of gene flow and the stabilizing influence of large interbreeding populations.(Mayr 1954) These populations exemplified "ecotypic variation." Peripherally isolated populations, in contrast, possess "typostrophic variation" which "have the characteristic features of incipient species, but what is more important they often are species or incipient species of an entirely new type. That is, they may have morphological or ecological features that deviate quite strikingly and unexpectedly from the parental 'pattern' " (1954:160) Year 1954 (MCMLIV) was a common year starting on Friday of the Gregorian calendar. ... Gene flow (also known as gene migration) is the transfer of genes from one population to another. ...


Stephen Jay Gould summarized the theory, and its consequences for punctuated equilibrium, in a 1977 essay for Natural History: For the album by Ash, see 1977 (album). ... Natural History is a magazine on science and nature aimed at the general public which is published by the American Museum of Natural History. ...

"A new species can arise when a small segment of the ancestral population is isolated at the periphery of the ancestral range. Large, stable central populations exert a strong homogenizing influence. New and favorable mutations are diluted by the sheer bulk of the population through which they must spread. They may build slowly in frequency, but changing environments usually cancel their selective value long before they reach fixation. Thus, phyletic transformation in large populations should be very rare—as the fossil record proclaims. But small, peripherally isolated groups are cut off from their parental stock. They live as tiny populations in geographic corners of the ancestral range. Selective pressures are usually intense because peripheries mark the edge of ecological tolerance for ancestral forms. Favorable variations spread quickly. Small peripheral isolates are a laboratory of evolutionary change.
"What should the fossil record include if most evolution occurs by speciation in peripheral isolates? Species should be static through their range because our fossils are the remains of large central populations. In any local area inhabited by ancestors, a descendant species should appear suddenly by migration from the peripheral region in which it evolved. In the peripheral region itself, we might find direct evidence of speciation, but such good fortune would be rare indeed because the event occurs so rapidly in such a small population. Thus, the fossil record is a faithful rendering of what evolutionary theory predicts, not a pitiful vestige of a once bountiful tale." (1980:184)

Common misconceptions

Confusion with other rapid modes of evolution

Punctuated equilibrium is often confused with George Gaylord Simpson's quantum evolution, Richard Goldschmidt's saltationism, pre-Lyellian catastrophism, and the phenomenon of mass extinction. Punctuated equilibrium is therefore mistakenly thought to oppose the concept of gradualism, when it is actually more appropriately understood as a form of gradualism (in the strict and literal sense of biological continuity).(Eldredge and Gould 1972) This is because even though evolutionary change aggregates "quickly" between geological sediments—relative to the species' full geological existence—change is still occurring incrementally, with no great change from one generation to the next. To this end, Gould later commented that: George Gaylord Simpson (June 16, 1902 - October 6, 1984) was an American paleontologist. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Richard Benedict Goldschmidt (* April 12, 1878; ± 24 April 1958) was a Jewish-German-American geneticist. ... In biology, saltation (from Latin, saltus, leap) is a sudden change from one generation to the next, that is large, or very large, in comparison with the usual variation of an organism. ... Catastrophism is the theory that Earth has been affected by sudden, short-lived, violent events that were sometimes worldwide in scope. ... An extinction event (also extinction-level event, ELE) is a period in time when a large number of species die out. ... Gradualism, in biology, holds that evolution occurs through the accumulation of slight modifications over a period of generations. ...

Most of our paleontological colleagues missed this insight because they had not studied evolutionary theory and either did not know about allopatric speciation or had not considered its translation to geological time. Our evolutionary colleagues also failed to grasp the implication, primarily because they did not think at geological scales. (Gould 1991)

The relationship between punctuationism and gradualism can be better appreciated by considering an example. Suppose the average length of a limb in a particular species grows 50 centimeters (20 inches) over 70,000 years—a large amount in a geologically short period of time. If the average generation is seven years, then our given time span corresponds to 10,000 generations. It is therefore reasonable to conclude that if the limb size in our hypothetical population evolved in the most conservative manner, it need only increase at a rate of 0.005 cm per generation (= 50 cm/10,000), despite its abrupt appearance in the geological record. Paleontology or palaeontology (see Spelling differences) is the study of the history and development of life on Earth, including that of ancient plants and animals, based on the fossil record (evidence of their prehistoric existence as typically preserved in sedimentary rocks). ... Allopatric speciation, also known as geographic speciation, occurs when populations physically isolated by an extrinsic barrier evolve intrinsic (genetic) reproductive isolation such that if the barrier between the populations breaks down, individuals of the two populations can no longer interbreed. ... For a non-technical introduction to the topic, please see Introduction to evolution. ... A centimetre (American spelling centimeter, symbol cm) is a unit of length that is equal to one hundredth of a metre, the current SI base unit of length. ... An inch (plural: inches; symbol or abbreviation: in or, sometimes, ″ - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ... In mathematics and statistics, the arithmetic mean (or simply the mean) of a list of numbers is the sum of all the members of the list divided by the number of items in the list. ...


Challenge of uniformity of rates

Critics of punctuated equilibrium, such as Richard Dawkins, have argued that the concept of phyletic gradualism was merely a straw man—arguing that a belief in the uniformity of rates was never really held by any serious evolutionist (Dawkins 1986, 223-224, 228). Eldredge and Gould's advocacy of the theory brought punctuated equilibrium much attention, including full page stories in The New York Times and Newsweek.(Adler and Carey 1982) The resulting debate stirred up in evolutionary circles and the lack of transitional fossils were represented by some creationists to portray Darwinism as a "theory in crisis." The actual differences between the various evolutionary theorists were not as large as they were made to appear (Dawkins 1986, 236). Gould himself later said that the theory did not in fact refute Darwin's gradualism [citation needed], but just added the ideas of catastrophism and stasis. Clinton Richard Dawkins (born March 26, 1941) is a British ethologist, evolutionary biologist and popular science writer who holds the Charles Simonyi Chair for the Public Understanding of Science at Oxford University. ... A straw man, or straw person, argument is a logical fallacy based on misrepresentation of an opponents position. ... 1986 (MCMLXXXVI) was a common year starting on Wednesday of the Gregorian calendar. ... The New York Times is a newspaper published in New York City by Arthur Ochs Sulzberger Jr. ... The Creation of Light by Gustave Doré. Creation refers to the concept that all humanity, life, the Earth, or the universe as a whole was created by a deity (often referred to as God). ...


Supplemental modes of rapid evolution

Recent work in developmental biology has identified dynamical and physical mechanisms of tissue morphogenesis that may underlie abrupt morphological transitions during evolution. Consequently, consideration of mechanisms of phylogenetic change that are actually (not just apparently) non-gradual is increasingly common in the field of evolutionary developmental biology, particularly in studies of the origin of morphological novelty. A description of such mechanisms can be found in the multi-authored volume Origination of Organismal Form (MIT Press; 2003). Views of a Foetus in the Womb, Leonardo da Vinci, ca. ... Morphogenesis is also the name of a band. ... Evolutionary developmental biology (evolution of development or informally, evo-devo) is a field of biology that compares the developmental processes of different animals in an attempt to determine the ancestral relationship between organisms and how developmental processes evolved. ... Origination of Organismal Form Beyond the Gene in Developmental and Evolutionary Biology Edited by Gerd Müller and Stuart Newman ISBN 0-262-13419-5 This book explores the multiple factors that may have been responsible for the origination of biological form in multicellular life. ...

See also: Rapid modes of evolution

Rapid modes of evolution have been proposed by several notable biologists ever since Charles Darwin proposed his theory of evolutionary descent by natural selection. ...

Relation to Darwinism

The sudden appearance and lack of substantial gradual change of most species in the geologic record—from their initial appearance until their extinction—has long been noted, including by Charles Darwin (1859:301, 1871:119-120) who appealed to the imperfection of the record as the favored explanation. Nevertheless, with the influence of catastrophism, Darwin needed to forcefully stress the gradual nature of evolution. It is often incorrectly assumed that he insisted that the rate of change must be constant, or nearly so. In The Origin of Species Darwin wrote that "the periods during which species have undergone modification, though long as measured in years, have probably been short in comparison with the periods during which they retain the same form." (1872:619) Thus punctuationism in general is consistent with Darwin's conception of evolution, and with the independent proposals of natural selection by William Charles Wells, Patrick Matthew, and Alfred Russel Wallace. Catastrophism is the theory that Earth has been affected by sudden, short-lived, violent events that were sometimes worldwide in scope. ... The Galápagos Islands hold 13 species of finches that are closely related and differ most markedly in the shape of their beaks. ... William Charles Wells (1757 — 1817) was Wells was born Charlestown, where? and was sent to school in Dumfries and later attended the University of Edinburgh. ... Patrick Matthew Patrick Matthew (20 October 1790 — 8 June 1874) was a Scottish fruit grower who had proposed the principle of natural selection as a mechanism of evolution over a quarter-century earlier than did Charles Darwin and Alfred Russel Wallace. ... Alfred Russel Wallace Alfred Russel Wallace, OM, FRS (January 8, 1823 – November 7, 1913) was a British naturalist, explorer, geographer, anthropologist and biologist. ...


According to the theory of punctuated equilibrium, "peripheral isolates" are considered to be of critical importance for speciation. However, Darwin wrote, "I can by no means agree…that immigration and isolation are necessary elements. . . . Although isolation is of great importance in the production of new species, on the whole I am inclined to believe that largeness of area is still more important, especially for the production of species which shall prove capable of enduring for a long period, and of spreading widely." (1859:105-106)


Darwin explained the reasons for this belief as follows:

"Throughout a great and open area, not only will there be a greater chance of favourable variations, arising from the large number of individuals of the same species there supported, but the conditions of life are much more complex from the large number of already existing species; and if some of these species become modified and improved, others will have to be improved in a corresponding degree, or they will be exterminated. Each new form, also, as soon as it has been improved, will be able to spread over the open and continuous area, and will thus come into competition with many other forms ... the new forms produced on large areas, which have already been victorious over many competitors, will be those that will spread most widely, and will give rise to the greatest number of new varieties and species. They will thus play a more important role in the changing history of the organic world." (1859:107-108)

Thus punctuated equilibrium contradicts some of Darwin's ideas regarding the specific mechanisms of evolution, but generally accords with Darwin's theory of evolution by natural selection.


In Social Theory

Punctuated Equilibrium has also played a role in social and political theory, particularly in policy studies, as one of many cross-overs of evolutionary theory into social theory. The punctuated equilibrium model of policy change was first presented by Frank Baumgartner and Bryan Jones in 1993, and has subsequently been examined in many policy contexts and has increasingly received attention in the field. The model states that policy generally changes only incrementally due to several restraints, namely lack of institutional change and bounded rationality of individual decision-making. Policy change will thus be punctuated by changes in these conditions, especially change in party control of government or changes in public opinion. Thus, policy is characterized by long periods of stability, punctuated by large, but rare, changes due to large shifts in society or government. This has been shown to be particularly useful in environmental policy and energy policy. Many models of human behavior in the social sciences assume that humans can be reasonably approximated or described as rational entities, especially as conceived by rational choice theory. ... Public Opinion is a book on media and democracy by Walter Lippmann. ... Environmental policy refers to the laws, regulations, and other policy mechanisms concerning environmental issues and sustainability. ... Energy policy is the manner a given entity (often governmental) has decided to address issues of energy production, distribution and consumption. ...


See also

Adaptive radiation describes the rapid speciation of a single or a few species to fill many ecological niches. ... Evolutionary capacitance is a cutting-edge biological theory stating that living systems have the ability to accumulate genetic variation that has no phenotypic effect until the system is disturbed (perhaps by stress), at which point the variation has a phenotypic effect and is subject to natural selection. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Hopeful Monster is the colloquial term used in evolutionary biology to describe an event of instantaneous-speciation, saltation, or systemic mutation, which contributes positively to the production of new major evolutionary groups. ... Punctuated gradualism is a macroevolutionary hypothesis that refers to a species that has relative stasis over a considerable part of its total duration [and] underwent periodic, relatively rapid, morphologic change that did not lead to lineage branching.[1] Phyletic gradualism Punctuated equilibrium ^ GeoScienceWorld article Evidence for punctuated gradualism in the... Phyletic gradualism is a macroevolutionary hypothesis rooted in uniformitarianism. ... Eruption column rising, Mount Redoubt, Alaska According to the Toba catastrophe theory, modern human evolution was affected by a recent, large volcanic event. ...

References

  • Adler, J. and Carey, J. (1982) "Enigmas of Evolution", Newsweek, March 29, 1982.
  • Brett, C. E., L. C. Ivany, and K. M. Schopf (1996) "Coordinated stasis: An overview." Palaeogeography Palaeoclimatology Palaeoecology 127 (1-4): 1-20.
  • Dawkins, R. (1986). The Blind Watchmaker. New York: W.W. Norton & Company.
  • Eldredge, N. and S. J. Gould (1972) "Punctuated equilibria: an alternative to phyletic gradualism" In T.J.M. Schopf, ed., Models in Paleobiology. San Francisco: Freeman Cooper. pp. 82-115. Reprinted in N. Eldredge Time frames. Princeton: Princeton Univ. Press. 1985
  • Erwin, D. H. and R. L. Anstey (1995) New approaches to speciation in the fossil record. New York : Columbia University Press.
  • Fitch, W. J. and F. J. Ayala (1995) Tempo and mode in evolution : genetics and paleontology 50 years after Simpson. Washington, D.C.: National Academy Press.
  • Ghiselin, M.T. (1986) "WE ARE ALL CONTRAPTIONS", The New York Times, December 14, 1986.
  • Gould, S. J. (1977) "Evolution's erratic pace." Natural History 86 (May): 12-16.
  • Gould, S. J. (1980) The Panda's Thumb. New York. W. W. Norton. pp. 182-184.
  • Gould, S. J. (1991) "Opus 200" Natural History 100 (August): 12-18.
  • Gould, S. J. (1992) "Punctuated equilibrium in fact and theory." In Albert Somit and Steven Peterson The Dynamics of Evolution. New York: Cornell University Press. pp. 54-84.
  • Gould, S. J. (2002) The Structure of Evolutionary Theory. Cambridge MA: Harvard Univ. Press.
  • Gould, S. J. and N. Eldredge (1993) "Punctuated equilibrium comes of age" Nature 366 (6452): 223-227.
  • Mayr, E. (1954) "Change of genetic environment and evolution" In J. Huxley, A. C. Hardy and E. B. Ford. Evolution as a Process London: Allen and Unwin. pp. 157-180.
  • Mayr, E. (1963) Animal Species and Evolution. Cambridge MA: Harvard University Press.
  • Mayr, E. (1992) "Speciational Evolution or Punctuated Equilibria" from Albert Somit and Steven Peterson The Dynamics of Evolution. New York: Cornell University Press. pp. 21-53.
  • Rhodes, R. H. T. (1983) "Gradualism, punctuated equilibrium and the Origin of Species." Nature 305 (5932): 269-272.
  • Shermer, M. (2001) The Borderlands of Science. New York: Oxford University Press.

Cover illustration by the zoologist Desmond Morris The Blind Watchmaker is a 1986 book by Richard Dawkins in which he presents an explanation of, and argument for, the theory of evolution by means of natural selection. ...

External links

Speciation guide
v  d  e
Basic concepts: species | chronospecies | speciation | cline
Modes of speciation: allopatric | peripatric | parapatric | sympatric | polyploidy
Auxiliary mechanisms: sexual selection | assortative mating | punctuated equilibrium
Intermediate stages: hybrid | Haldane's rule | ring species

  Results from FactBites:
 
Punctuated equilibrium - Wikipedia, the free encyclopedia (1633 words)
Punctuated equilibrium (or punctuated equilibria) is a theory in evolutionary biology which states that most sexually reproducing species will show little to no evolutionary change throughout their history.
Punctuated equilibrium is commonly contrasted against the theory of phyletic gradualism, which hypothesizes that most evolution occurs uniformly and by the steady and gradual transformation of whole lineages (anagenesis).
Punctuated equilibrium differed from Mayr simply in that Eldredge and Gould had placed considerably greater emphasis on stasis, whereas Mayr was generally concerned with explaining the morphological discontinuity (or punctuational patterns) found in the fossil record.
Punctuated Equilibrium (703 words)
Punctuated equilibrium, also called punctuated equilibria or the punctuational model, holds that genetic change occurs relatively rapidly on a geological timescale, and these shorter periods of evolution are sandwiched between longer periods of “stasis,”
Proponents of the punctuational model have relied heavily upon the work of mathematician Sewall Wright, who observed that novel variation was more likely to become fixed in small populations which were reproductively isolated (often due to geographic factors) from the main population.
One primary difference between the punctuational and gradualistic models of evolution is thus that under the gradualistic model, the entire parent population slowly morphs into the descendant species.
  More results at FactBites »

 
 

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