Article

Stasis

Scott Lidgard and Melanie Hopkins

in Evolutionary Biology


Published online August 2015 | | DOI: http://dx.doi.org/10.1093/obo/9780199941728.016.0067

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In modern biology, stasis refers primarily to a relative lack of evolutionary change over a long period during the history of a species. It is one of the key facets of macroevolution, or evolution that takes place at or above the level of the species. Stasis is frequently associated with the theory of punctuated equilibrium, in which most evolutionary change is concentrated during the phylogenetic branching of lineages in very rapid bursts of speciation. Much longer episodes of relative morphological invariance, or stasis, follow speciation events. Stasis is also contrasted with incremental directional change within and between related lineages (gradualism), and sometimes with lineage patterns that cannot be distinguished from random trends. The idea of stasis is hardly new. Notions of the fixity of species in space and time extend back well before biology became a recognized science, and these notions have influenced thinking about evolution from before Darwin until today. While most discussion begins with lineages of interrelated populations of organisms at or near species level, the idea of stasis has also been applied to other levels of biological hierarchy for entities other than species: morphological traits, highly conserved genes, ecological communities, and more. How species stasis is recognized as an evolutionary pattern depends, in part, upon how species are discriminated and which species concepts are used, which properties are measured, and methods of analysis. The dynamics and causes of macroevolution are crucial, yet still unsettled, problems in evolutionary biology, either invoking or questioning the extrapolation of microevolutionary mechanisms to explain protracted temporal patterns such as stasis.

Article.  15288 words. 

Subjects: Evolutionary Biology

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