Saltation (biology)
Encyclopedia
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. The term is used for occasionally hypothesized, nongradual changes (especially single-step speciation
) that are atypical of, or violate, standard concepts - gradualism
- involved in neo-Darwinian evolution
.
Saltation was the idea that new species arise as a result of large mutations. It was seen as a much faster alternative to the Darwinian concept of a gradual process of small random variations being acted on by natural selection. It was popular with early geneticists such as Hugo de Vries
, who along with Carl Correns
helped rediscover Gregor Mendel
's laws of inheritance in 1900, William Bateson
, a British zoologist who switched to genetics, and early in his career Thomas Hunt Morgan
. Some of these geneticists developed it into the mutation theory of evolution.
Saltation does not fit into contemporary evolutionary theory, but there are some prominent proponents, including Carl Woese
. Woese, and colleagues, suggested that the absence of RNA signature continuum between domains
of bacteria
, archaea
, and eukarya constitutes a primary indication that the three primary organismal lineages materialized via one or more major evolutionary saltations from some universal ancestral state involving dramatic change in cellular organization that was significant early in the evolution of life, but in complex organisms gave way to the generally accepted Darwinian mechanisms.
Polyploidy
(most common in plants but not unknown in animals) is considered a type of saltation, even though most polyploid individuals are sterile. Polyploidy meets the basic criteria of saltation in that a significant change (in gene numbers) results in speciation in just one generation. Mammalian liver cells are typically polyploidal, but they are not part of the germ line.
is a saltationist theory, often mistaken for Richard Goldschmidt's
hypothesis of "Hopeful Monsters."
However, punctuated equilibrium refers instead to a pattern of evolution where most speciation
occurs relatively rapidly from a geological perspective (tens of thousands of years instead of millions of years), but through neo-Darwinian evolution, not by saltations.
argued that the recent discovery of regulatory genes
offered new evidence which supported some of Goldschmidt's postulates. Gould argued that instances of rapid evolution neither undermine Darwinian theory
(as Goldschmidt believed) nor await immediate discreditation (as many neo-Darwinians thought). Gould insisted that Darwin's
belief in gradualism
—which was largely inherited from the anti-catastrophic views of Charles Lyell
—was never an essential component to Darwin's theory of evolution. Thomas Henry Huxley also warned Darwin that he had loaded his work "with an unnecessary difficulty in adopting Natura non facit saltum
so unreservedly." Huxley feared this assumption could discourage naturalists who believed that major leaps and cataclysms played a significant role in the history of life. Gould continued:
Nevertheless, Gould argued that Goldschmidt's "hopeful monster" concept was incorrect:
opposed the theory of gradual evolution, and in the 1930s suggested that major evolutionary transformations must have occurred in large leaps between species due to macromutation. This idea became known as the "Hopeful Monster" theory and was further taken and developed up by the German-born geneticist
Richard Goldschmidt
in the 1940s. Schindewolf was also the first to suggest, in 1950, that mass extinctions might have been caused by extraterrestrial impacts or nearby supernova.
Goldschmidt thought that small gradual changes could not bridge the hypothetical divide between microevolution
and macroevolution
. In his seminal work The Material Basis of Evolution (1940), he wrote "the change from species to species is not a change involving more and more additional atomistic changes, but a complete change of the primary pattern or reaction system into a new one, which afterwards may again produce intraspecific variation by micromutation."
Goldschmidt's thesis however was universally rejected and widely ridiculed within the biological community, which favored the neo-Darwinian
explanations of R.A. Fisher
, J. B. S. Haldane
and Sewall Wright
.
Soren Lovtrup advocated a similar hypothesis of macromutation to Goldschmidt's in 1974. Lovtrup, a biochemist
and embryologist from Denmark, believed that macromutations interfered with various epigenetic processes, that is, those which affect the casual processes in biological development. This is in contrast to the gradualistic theory of micromutations of Neo-Darwinism
which claims that evolutionary innovations are generally the result of accumulation of numerous very slight modifications. Lovtrup also rejected the punctuated equilibria of Stephen Gould
and Niles Eldredge
claiming it was a form of gradualism and not a macromutation theory. Lovtrup defended many of Darwin's critics including Schindewolf, Mivart, Goldschmidt, and Himmelfarb.
Mae Wan Ho described Lovtrup's theory as similar to the hopeful monster theory of Richard Goldschmidt
.
to associate Goldschmidt's "hopeful monsters" with the theory of punctuated equilibrium
, as proposed by Eldredge and Gould. Punctuated equilibrium differs from hopeful monsters in that the former acts on populations rather than individuals, is theoretically more gradual (which proposes to take 50,000 to 100,000 years), functions by the evolution of reproductive isolation (through mechanisms such as allopatric speciation
), and the latter says nothing of stasis. Creationists such as Luther Sutherland claim that both theories inadvertently appeal to the absence of fossil evidence for evolution and thereby undermining the theory of Darwinian evolution. This predicament is used by creationists to argue that "there are no transitional fossil
s." Paleontologists such as Niles Eldredge
, Stephen Jay Gould
, and Steven M. Stanley
avoid this by explaining that transitional forms may be rare between species, but "they are abundant between larger groups", and none of these paleontologists support Goldschmidt's "hopeful monster" hypothesis
.
Steven M. Stanley
argued that some of Goldschmidt's views err mainly in exaggerating the importance of "chromosomal rearrangements" leading to "rapid changes in growth gradients or developmental sequences, and on what we now call quantum speciation."
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
, ""saltation"" (from Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
, 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. The term is used for occasionally hypothesized, nongradual changes (especially single-step speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
) that are atypical of, or violate, standard concepts - gradualism
Gradualism
Gradualism is the belief in or the policy of advancing toward a goal by gradual, often slow stages.-Politics and society:In politics, the concept of gradualism is used to describe the belief that change ought to be brought about in small, discrete increments rather than in abrupt strokes such as...
- involved in neo-Darwinian evolution
Modern evolutionary synthesis
The modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...
.
Saltation was the idea that new species arise as a result of large mutations. It was seen as a much faster alternative to the Darwinian concept of a gradual process of small random variations being acted on by natural selection. It was popular with early geneticists such as Hugo de Vries
Hugo de Vries
Hugo Marie de Vries ForMemRS was a Dutch botanist and one of the first geneticists. He is known chiefly for suggesting the concept of genes, rediscovering the laws of heredity in the 1890s while unaware of Gregor Mendel's work, for introducing the term "mutation", and for developing a mutation...
, who along with Carl Correns
Carl Correns
Carl Erich Correns was a German botanist and geneticist, who is notable primarily for his independent discovery of the principles of heredity, and for his rediscovery of Gregor Mendel's earlier paper on that subject, which he achieved simultaneously but independently of the botanists Erich...
helped rediscover Gregor Mendel
Gregor Mendel
Gregor Johann Mendel was an Austrian scientist and Augustinian friar who gained posthumous fame as the founder of the new science of genetics. Mendel demonstrated that the inheritance of certain traits in pea plants follows particular patterns, now referred to as the laws of Mendelian inheritance...
's laws of inheritance in 1900, William Bateson
William Bateson
William Bateson was an English geneticist and a Fellow of St. John's College, Cambridge...
, a British zoologist who switched to genetics, and early in his career Thomas Hunt Morgan
Thomas Hunt Morgan
Thomas Hunt Morgan was an American evolutionary biologist, geneticist and embryologist and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries relating the role the chromosome plays in heredity.Morgan received his PhD from Johns Hopkins University in zoology...
. Some of these geneticists developed it into the mutation theory of evolution.
Saltation does not fit into contemporary evolutionary theory, but there are some prominent proponents, including Carl Woese
Carl Woese
Carl Richard Woese is an American microbiologist and physicist. Woese is famous for defining the Archaea in 1977 by phylogenetic taxonomy of 16S ribosomal RNA, a technique pioneered by Woese and which is now standard practice. He was also the originator of the RNA world hypothesis in 1977,...
. Woese, and colleagues, suggested that the absence of RNA signature continuum between domains
Domain (biology)
In biological taxonomy, a domain is the highest taxonomic rank of organisms, higher than a kingdom. According to the three-domain system of Carl Woese, introduced in 1990, the Tree of Life consists of three domains: Archaea, Bacteria and Eukarya...
of bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
, and eukarya constitutes a primary indication that the three primary organismal lineages materialized via one or more major evolutionary saltations from some universal ancestral state involving dramatic change in cellular organization that was significant early in the evolution of life, but in complex organisms gave way to the generally accepted Darwinian mechanisms.
Polyploidy
Polyploidy
Polyploid is a term used to describe cells and organisms containing more than two paired sets of chromosomes. Most eukaryotic species are diploid, meaning they have two sets of chromosomes — one set inherited from each parent. However polyploidy is found in some organisms and is especially common...
(most common in plants but not unknown in animals) is considered a type of saltation, even though most polyploid individuals are sterile. Polyploidy meets the basic criteria of saltation in that a significant change (in gene numbers) results in speciation in just one generation. Mammalian liver cells are typically polyploidal, but they are not part of the germ line.
Confusion with punctuated equilibrium
It is a popular misconception that punctuated equilibriumPunctuated equilibrium
Punctuated equilibrium is a theory in evolutionary biology which proposes that most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state called stasis...
is a saltationist theory, often mistaken for Richard Goldschmidt's
Richard Goldschmidt
Richard Benedict Goldschmidt was a German-born American geneticist. He is considered the first to integrate genetics, development, and evolution. He pioneered understanding of reaction norms, genetic assimilation, dynamical genetics, sex determination, and heterochrony...
hypothesis of "Hopeful Monsters."
However, punctuated equilibrium refers instead to a pattern of evolution where most speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
occurs relatively rapidly from a geological perspective (tens of thousands of years instead of millions of years), but through neo-Darwinian evolution, not by saltations.
Stephen Jay Gould
In 1977 Stephen Jay GouldStephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
argued that the recent discovery of regulatory genes
Gene regulatory network
A gene regulatory network or genetic regulatory network is a collection of DNA segments in a cell whichinteract with each other indirectly and with other substances in the cell, thereby governing the rates at which genes in the network are transcribed into mRNA.In general, each mRNA molecule goes...
offered new evidence which supported some of Goldschmidt's postulates. Gould argued that instances of rapid evolution neither undermine Darwinian theory
Darwinism
Darwinism is a set of movements and concepts related to ideas of transmutation of species or of evolution, including some ideas with no connection to the work of Charles Darwin....
(as Goldschmidt believed) nor await immediate discreditation (as many neo-Darwinians thought). Gould insisted that Darwin's
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
belief in gradualism
Gradualism
Gradualism is the belief in or the policy of advancing toward a goal by gradual, often slow stages.-Politics and society:In politics, the concept of gradualism is used to describe the belief that change ought to be brought about in small, discrete increments rather than in abrupt strokes such as...
—which was largely inherited from the anti-catastrophic views of Charles Lyell
Charles Lyell
Sir Charles Lyell, 1st Baronet, Kt FRS was a British lawyer and the foremost geologist of his day. He is best known as the author of Principles of Geology, which popularised James Hutton's concepts of uniformitarianism – the idea that the earth was shaped by slow-moving forces still in operation...
—was never an essential component to Darwin's theory of evolution. Thomas Henry Huxley also warned Darwin that he had loaded his work "with an unnecessary difficulty in adopting Natura non facit saltum
Natura non facit saltus
Natura non facit saltum has been a principle of natural philosophy since at least Aristotle's time. It appears as an axiom in the works of Gottfried Leibniz and Isaac Newton, the co-inventors of the infinitesimal calculus, see Law of Continuity...
so unreservedly." Huxley feared this assumption could discourage naturalists who believed that major leaps and cataclysms played a significant role in the history of life. Gould continued:
As a Darwinian, I wish to defend Goldschmidt's postulate that macroevolution is not simply microevolution extrapolated, and that major structural transitions can occur rapidly without a smooth series of intermediate stages. . . . In his infamous book of 1940, Goldschmidt specifically invokes rate genes as a potential maker of hopeful monsters: 'This basis is furnished by the existence of mutants producing monstrosities of the required type and the knowledge of embryonic determination, which permits a small rate change in early embryonic processes to produce a large effect embodying considerable parts of the organism.' In my own, strongly biased opinion, the problem of reconciling evident discontinuity in macroevolution with Darwinism is largely solved by the observation that small changes early in embryology accumulate through growth to yield profound differences among adults.
Nevertheless, Gould argued that Goldschmidt's "hopeful monster" concept was incorrect:
The developmental theme of the 'hopeful monster' (despite its inappropriate name, virtually guaranteed to inspire ridicule and opposition), based on the important concept of 'rate genes,' came first in Goldschmidt's thought, and always occupied more of his attention and research. Unfortunately, he bound this interesting challenge from development, a partially valid concept that could have been incorporated into a Darwinian framework as an auxiliary hypothesis (and now has been accepted, to a large extent, if under different names), to his truly oppositional and ultimately incorrect theory of systemic mutation, therefore winning anathema for his entire system. Goldschmidt may have acted as the architect of his own undoing, but much of his work should evoke sympathetic attention today.
Macromutation theory
German paleontologist Otto SchindewolfOtto Schindewolf
Otto Heinrich Schindewolf was a German paleontologist who studied the evolution of corals and cephalopods....
opposed the theory of gradual evolution, and in the 1930s suggested that major evolutionary transformations must have occurred in large leaps between species due to macromutation. This idea became known as the "Hopeful Monster" theory and was further taken and developed up by the German-born geneticist
Geneticist
A geneticist is a biologist who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a researcher or lecturer. Some geneticists perform experiments and analyze data to interpret the inheritance of skills. A geneticist is also a Consultant or...
Richard Goldschmidt
Richard Goldschmidt
Richard Benedict Goldschmidt was a German-born American geneticist. He is considered the first to integrate genetics, development, and evolution. He pioneered understanding of reaction norms, genetic assimilation, dynamical genetics, sex determination, and heterochrony...
in the 1940s. Schindewolf was also the first to suggest, in 1950, that mass extinctions might have been caused by extraterrestrial impacts or nearby supernova.
Goldschmidt thought that small gradual changes could not bridge the hypothetical divide between microevolution
Microevolution
Microevolution is the changes in allele frequencies that occur over time within a population. This change is due to four different processes: mutation, selection , gene flow, and genetic drift....
and macroevolution
Macroevolution
Macroevolution is evolution on a scale of separated gene pools. Macroevolutionary studies focus on change that occurs at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes within a species or population.The process of speciation may fall...
. In his seminal work The Material Basis of Evolution (1940), he wrote "the change from species to species is not a change involving more and more additional atomistic changes, but a complete change of the primary pattern or reaction system into a new one, which afterwards may again produce intraspecific variation by micromutation."
Goldschmidt's thesis however was universally rejected and widely ridiculed within the biological community, which favored the neo-Darwinian
Neo-Darwinism
Neo-Darwinism is the 'modern synthesis' of Darwinian evolution through natural selection with Mendelian genetics, the latter being a set of primary tenets specifying that evolution involves the transmission of characteristics from parent to child through the mechanism of genetic transfer, rather...
explanations of R.A. Fisher
Ronald Fisher
Sir Ronald Aylmer Fisher FRS was an English statistician, evolutionary biologist, eugenicist and geneticist. Among other things, Fisher is well known for his contributions to statistics by creating Fisher's exact test and Fisher's equation...
, J. B. S. Haldane
J. B. S. Haldane
John Burdon Sanderson Haldane FRS , known as Jack , was a British-born geneticist and evolutionary biologist. A staunch Marxist, he was critical of Britain's role in the Suez Crisis, and chose to leave Oxford and moved to India and became an Indian citizen...
and Sewall Wright
Sewall Wright
Sewall Green Wright was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. He is the discoverer of the inbreeding coefficient and of...
.
Soren Lovtrup advocated a similar hypothesis of macromutation to Goldschmidt's in 1974. Lovtrup, a biochemist
Biochemist
Biochemists are scientists who are trained in biochemistry. Typical biochemists study chemical processes and chemical transformations in living organisms. The prefix of "bio" in "biochemist" can be understood as a fusion of "biological chemist."-Role:...
and embryologist from Denmark, believed that macromutations interfered with various epigenetic processes, that is, those which affect the casual processes in biological development. This is in contrast to the gradualistic theory of micromutations of Neo-Darwinism
Neo-Darwinism
Neo-Darwinism is the 'modern synthesis' of Darwinian evolution through natural selection with Mendelian genetics, the latter being a set of primary tenets specifying that evolution involves the transmission of characteristics from parent to child through the mechanism of genetic transfer, rather...
which claims that evolutionary innovations are generally the result of accumulation of numerous very slight modifications. Lovtrup also rejected the punctuated equilibria of Stephen Gould
Stephen Gould
Stephen Gould is an American heldentenor, born in Virginia.Having started in musical theatre, in 2006 he performed the title-role of Siegfried in Wagner's Der Ring des Nibelungen at Bayreuth...
and Niles Eldredge
Niles Eldredge
Niles Eldredge is an American paleontologist, who, along with Stephen Jay Gould, proposed the theory of punctuated equilibrium in 1972.-Education:...
claiming it was a form of gradualism and not a macromutation theory. Lovtrup defended many of Darwin's critics including Schindewolf, Mivart, Goldschmidt, and Himmelfarb.
Mae Wan Ho described Lovtrup's theory as similar to the hopeful monster theory of Richard Goldschmidt
Richard Goldschmidt
Richard Benedict Goldschmidt was a German-born American geneticist. He is considered the first to integrate genetics, development, and evolution. He pioneered understanding of reaction norms, genetic assimilation, dynamical genetics, sex determination, and heterochrony...
.
Use by creationists
It has been common practice for creationistsCreationism
Creationism is the religious beliefthat humanity, life, the Earth, and the universe are the creation of a supernatural being, most often referring to the Abrahamic god. As science developed from the 18th century onwards, various views developed which aimed to reconcile science with the Genesis...
to associate Goldschmidt's "hopeful monsters" with the theory of punctuated equilibrium
Punctuated equilibrium
Punctuated equilibrium is a theory in evolutionary biology which proposes that most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state called stasis...
, as proposed by Eldredge and Gould. Punctuated equilibrium differs from hopeful monsters in that the former acts on populations rather than individuals, is theoretically more gradual (which proposes to take 50,000 to 100,000 years), functions by the evolution of reproductive isolation (through mechanisms such as allopatric speciation
Allopatric speciation
Allopatric speciation or geographic speciation is speciation that occurs when biological populations of the same species become isolated due to geographical changes such as mountain building or social changes such as emigration...
), and the latter says nothing of stasis. Creationists such as Luther Sutherland claim that both theories inadvertently appeal to the absence of fossil evidence for evolution and thereby undermining the theory of Darwinian evolution. This predicament is used by creationists to argue that "there are no transitional fossil
Transitional fossil
A transitional fossil is any fossilized remains of a lifeform that exhibits characteristics of two distinct taxonomic groups. A transitional fossil is the fossil of an organism near the branching point where major individual lineages diverge...
s." Paleontologists such as Niles Eldredge
Niles Eldredge
Niles Eldredge is an American paleontologist, who, along with Stephen Jay Gould, proposed the theory of punctuated equilibrium in 1972.-Education:...
, Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
, and Steven M. Stanley
Steven M. Stanley
Steven M. Stanley is an American paleontologist and evolutionary biologist at the University of Hawaii at Manoa. He is best known for his empirical research documenting the evolutionary process of punctuated equilibrium in the fossil record.Stanley received his Ph.D. from Yale University in 1968...
avoid this by explaining that transitional forms may be rare between species, but "they are abundant between larger groups", and none of these paleontologists support Goldschmidt's "hopeful monster" hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
.
Steven M. Stanley
Steven M. Stanley
Steven M. Stanley is an American paleontologist and evolutionary biologist at the University of Hawaii at Manoa. He is best known for his empirical research documenting the evolutionary process of punctuated equilibrium in the fossil record.Stanley received his Ph.D. from Yale University in 1968...
argued that some of Goldschmidt's views err mainly in exaggerating the importance of "chromosomal rearrangements" leading to "rapid changes in growth gradients or developmental sequences, and on what we now call quantum speciation."
See also
- CatastrophismCatastrophismCatastrophism is the theory that the Earth has been affected in the past by sudden, short-lived, violent events, possibly worldwide in scope. The dominant paradigm of modern geology is uniformitarianism , in which slow incremental changes, such as erosion, create the Earth's appearance...
- Phyletic gradualismPhyletic gradualismPhyletic gradualism is a model of evolution which theorizes that most speciation is slow, uniform and gradual. When evolution occurs in this mode, it is usually by the steady transformation of a whole species into a new one...
- Rapid modes of evolutionRapid modes of evolutionRapid modes of evolution have been proposed by several notable biologists ever since Charles Darwin proposed his theory of evolutionary descent by natural selection...
- Leo S. Berg
- History of evolutionary thoughtHistory of evolutionary thoughtEvolutionary thought, the conception that species change over time, has roots in antiquity, in the ideas of the ancient Greeks, Romans, and Chinese as well as in medieval Islamic science...
- Eclipse of Darwinism