Punctuated Equilibrium Theory
A Punctuated Equilibrium Theory is an theory of evolution where rates of morphological evolution very over time, often with periods of long stasis interspersed with periods of rapid change.
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- Counter-Example(s):
- See: Cladogenesis, Allopatric Speciation, Fossil, Evolution, Species, Geologic Time Scale.
References
2015
- (Wikipedia, 2015) ⇒ http://en.wikipedia.org/wiki/Punctuated_equilibrium Retrieved:2015-5-5.
- Punctuated equilibrium (also called punctuated equilibria) is a theory in evolutionary biology which proposes that once formed most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state of stasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and rapid (on a geologic time scale) events of branching speciation called cladogenesis. Cladogenesis is the process by which a species splits into two distinct species, rather than one species gradually transforming into another.[1] Punctuated equilibrium is commonly contrasted against phyletic gradualism, the belief that evolution generally occurs uniformly and by the steady and gradual transformation of whole lineages (called anagenesis). In this view, evolution is seen as generally smooth and continuous.
In 1972, paleontologists Niles Eldredge and Stephen Jay Gould published a landmark paper developing their theory and called it punctuated equilibria.[2] Their paper built upon Ernst Mayr's model of geographic speciation,[3] I. Michael Lerner's theories of developmental and genetic homeostasis, [4] as well as their own empirical research. Eldredge and Gould proposed that the degree of gradualism commonly attributed to Charles Darwin is virtually nonexistent in the fossil record, and that stasis dominates the history of most fossil species.
- Punctuated equilibrium (also called punctuated equilibria) is a theory in evolutionary biology which proposes that once formed most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state of stasis. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and rapid (on a geologic time scale) events of branching speciation called cladogenesis. Cladogenesis is the process by which a species splits into two distinct species, rather than one species gradually transforming into another.[1] Punctuated equilibrium is commonly contrasted against phyletic gradualism, the belief that evolution generally occurs uniformly and by the steady and gradual transformation of whole lineages (called anagenesis). In this view, evolution is seen as generally smooth and continuous.
- ↑ Gould, Stephen Jay, & Eldredge, Niles (1977). "Punctuated equilibria: the tempo and mode of evolution reconsidered." Paleobiology 3 (2): 115-151. (p.145)
- ↑ Eldredge, Niles 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, pp. 193-223.
- ↑ Mayr, Ernst (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.
- ↑ Lerner, Israel Michael (1954). Genetic Homeostasis. New York: John Wiley.
- (Trivers, 2015) ⇒ Robert Trivers. (2015). “Vignettes of Famous Evolutionary Biologists, Large and Small.” In: The UNZ Review, April 27, 2015
- QUOTE: Many of us theoretical biologists who knew Stephen personally thought he was something of an intellectual fraud precisely because he had a talent for coining terms that promised more than they could deliver, while claiming exactly the opposite. One example was the notion of “punctuated equilibria” — which simply asserted that rates of (morphological) evolution were not constant, but varied over time, often with periods of long stasis interspersed with periods of rapid change. All of this was well known from the time of Darwin. The classic example were bats. They apparently evolved very quickly from small non-flying mammals (in perhaps less than 20 million years) but then stayed relatively unchanged once they reached the bat phenotype we are all familiar with today (about 50 million years ago). Nothing very surprising here, intermediate forms were apt to be neither very good classic mammals, nor good flying ones either, so natural selection pushed them rapidly through the relevant evolutionary space.
But Steve wanted to turn this into something grander, a justification for replacing natural selection (favoring individual reproductive success) with something called species selection. Since one could easily imagine that there was rapid turnover of species during periods of intense selection and morphological change, one might expect species selection to be more intense, while during the rest of the equilibrium stabilizing selection would rule throughout. But rate of species turnover has nothing to do with the traits within species — only with the relative frequency of species showing these traits.
- QUOTE: Many of us theoretical biologists who knew Stephen personally thought he was something of an intellectual fraud precisely because he had a talent for coining terms that promised more than they could deliver, while claiming exactly the opposite. One example was the notion of “punctuated equilibria” — which simply asserted that rates of (morphological) evolution were not constant, but varied over time, often with periods of long stasis interspersed with periods of rapid change. All of this was well known from the time of Darwin. The classic example were bats. They apparently evolved very quickly from small non-flying mammals (in perhaps less than 20 million years) but then stayed relatively unchanged once they reached the bat phenotype we are all familiar with today (about 50 million years ago). Nothing very surprising here, intermediate forms were apt to be neither very good classic mammals, nor good flying ones either, so natural selection pushed them rapidly through the relevant evolutionary space.