- Phyletic gradualism
Phyletic gradualism is a macroevolutionary
hypothesis rooted in uniformitarianism. The hypothesis states that species continue to adapt to new challenges over the course of their history, gradually becoming new species. Gradualism holds that every individual is the samespecies as its parents, and that there is no clear line of demarcation between the old species and the new species. It holds that the species is not a fixed type, and that thepopulation , not the individual, evolves. During this process,evolution occurs at a slow and smooth (but not necessarily constant) rate, even on a geological timescale. (cf.punctuated equilibrium ) [cite web|url=http://www.economist.com/science/displaystory.cfm?story_id=7995205|title=Unity and diversity|publisher=The Economist|accessdate=2006-10-05]Phyletic gradualism has been largely deprecated as the exclusive pattern of evolution by modern evolutionary biologists in favor of the acceptation of occurrence of patterns such as those described on
punctuated equilibrium ,quantum evolution , andpunctuated gradualism .Authors such as
Richard Dawkins argue that such constant-rate gradualism is not present in academic literature, serving only as astraw-man for punctuated equilibrium advocates. He refutes the idea that Charles Darwin himself was a constant-rate gradualist, as suggested byStephen Jay Gould , for Darwin has explicitly stated that "Many species, once formed, never undergo any further change...; and the periods, during which species have undergone modification, though long as measured by years, have probably been short in comparison with the periods during which they retain the same form."ources
* [http://www.blackwellpublishing.com/ridley/a-z/Phyletic_gradualism.asp The distinction between phyletic gradualism and punctuated equilibrium models]
* DAWKINS, Richard. "The Blind Watchmaker - Why the evidence of evolution reveals a universe without design". W. W. Norton & Company. New York, 1996References
The theory of the punctuated equilibrium goes against the theory of phyletic gradualism.
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