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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 does not fit into contemporary evolutionary theory[citation needed], 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.[1]
Polyploidy (most common in plants but not unknown in animals) can be seen as a type of saltation[dubious ], even though most polyploid individuals are sterile[verification needed]. 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.
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Punctuated Equilibrium
It is a popular misconception that punctuated equilibrium is a saltationist theory, often mistaken for Richard Goldschmidt's hypothesis of "Hopeful Monsters."[2] 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.
Pop Culture
In popular culture, a form of saltation appears to have emerged from misconceptions over currently accepted theories of evolution (the X-men and its various spin-offs being the most egregious examples). It was also fictionalized in Greg Bear's novel, Darwin's Radio.
The Teenage Mutant Ninja Turtles ( and many other, similar science-fiction pieces ) are not examples of saltationism, however. A saltation would be a substantial change that takes place during reproduction; a case when a child belongs to a different species than its parents - between generations, not during a generation.
See also
- Catastrophism
- Phyletic gradualism
- Rapid modes of evolution
- The Blind Watchmaker
- History of evolutionary thought
- Eclipse of Darwinism
Notes and references
- ^ Elijah Roberts, Anurag Sethi†, Jonathan Montoya, Carl R. Woese, and Zaida Luthey-Schulten (May 19, 2008). "Molecular signatures of ribosomal evolution". Proceedings of the National Academy of Sciences. http://www.pnas.org/content/105/37/13953.full?sid=f3651397-00e9-4a57-802b-f41c6ef6cf5a.
- ^ Gould, Stephen Jay. "Punctuated Equilibrium's Threefold History". The Structure of Evolutionary Theory. Harvard University Press. pp. 1006–1021. "[T]he urban legend rests on the false belief that ... punctuated equilibrium became a saltational theory wedded to Goldschmidt's hopeful monsters as a mechanism. I have labored to refute this nonsensical charge from the day I first heard it."
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