Editing Gradualism (section)

==Geology and biology==
{{further|Alternatives to Darwinism}}

In the natural sciences, gradualism is the [[theory]] which holds that profound change is the cumulative product of slow but continuous processes, often contrasted with [[catastrophism]].  The theory was proposed in 1795 by [[James Hutton]], a Scottish geologist, and was later incorporated into [[Charles Lyell]]'s theory of [[Uniformitarianism (science)|uniformitarianism]].  Tenets from both theories were applied to [[biology]] and formed the basis of early [[evolution]]ary theory.

[[Charles Darwin]] was influenced by Lyell's ''Principles of Geology'', which explained both uniformitarian methodology and theory. Using uniformitarianism, which states that one cannot make an appeal to any force or phenomenon which cannot presently be observed (see [[catastrophism]]), Darwin theorized that the evolutionary process must occur gradually, not in [[Saltation (biology)|saltations]], since saltations are not presently observed, and extreme deviations from the usual phenotypic variation would be more likely to be selected against.

Gradualism is often confused with the concept of [[phyletic gradualism]]. It is a term coined by [[Stephen Jay Gould]] and [[Niles Eldredge]] to contrast with their model of [[punctuated equilibrium]], which is gradualist itself, but argues that most evolution is marked by long periods of evolutionary stability (called stasis), which is punctuated by rare instances of branching evolution.<ref name=punc1972>Eldredge, Niles, and S. J. Gould (1972). [http://www.blackwellpublishing.com/ridley/classictexts/eldredge.pdf "Punctuated equilibria: an alternative to phyletic gradualism"]. In T.J.M. Schopf, ed., ''Models in Paleobiology''. San Francisco: Freeman, Cooper and Company, pp. 82-115.</ref>

[[Phyletic gradualism]] is a model of [[evolution]] which theorizes that most [[speciation]] is slow, uniform and gradual.<ref name=pe1972>Eldredge, N. and S. J. Gould (1972). [http://www.blackwellpublishing.com/ridley/classictexts/eldredge.asp "Punctuated equilibria: an alternative to phyletic gradualism"] In T.J.M. Schopf, ed., ''Models in Paleobiology''. San Francisco: Freeman Cooper. p. 84.</ref> When evolution occurs in this mode, it is usually by the steady transformation of a whole [[species]] into a new one (through a process called [[anagenesis]]). In this view no clear line of demarcation exists between an ancestral species and a descendant species, unless [[cladogenesis|splitting]] occurs.

[[Punctuated gradualism]] is a [[microevolution]]ary [[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". It is one of the three common models of [[evolution]]. While the traditional model of palaeontology, the phylogenetic model, states that features evolved slowly without any direct association with speciation, the relatively newer and more controversial idea of [[punctuated equilibrium]] claims that major evolutionary changes do not happen over a gradual period but in localized, rare, rapid events of branching speciation.  Punctuated gradualism is considered to be a variation of these models, lying somewhere in between the [[phyletic gradualism]] model and the punctuated equilibrium model. It states that speciation is not needed for a lineage to rapidly evolve from one equilibrium to another but may show rapid transitions between long-stable states.