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t. e. In evolutionary biology, punctuated equilibrium (also called punctuated equilibria) is a theory that proposes that once a species appears in the fossil record, the population will become stable, showing little evolutionary change for most of its geological history. [1] This state of little or no morphological change is called stasis.
Category. v. t. e. Punctuated gradualism is a microevolutionary 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.
Punctuated equilibrium in social theory is a conceptual framework for understanding the process of change in complex social systems. The approach studies the evolution of policy change, [1] including the evolution of conflicts. [2] The theory posits that most social systems exist in an extended period of stasis, which may be punctuated by ...
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 ...
Punctuated equilibrium and phyletic gradualism are not mutually exclusive (as Simpson's work demonstrates), and examples of each have been documented in different lineages. The debate between these two models is often misunderstood by non-scientists, and according to Richard Dawkins has been oversold by the media. [ 45 ]
The word phyletic derives from the Greek φυλετικός phūletikos, which conveys the meaning of a line of descent. [2] Phyletic gradualism contrasts with the theory of punctuated equilibrium, which proposes that most evolution occurs isolated in rare episodes of rapid evolution, when a single species splits into two distinct species, followed by a long period of stasis or non-change.
Gould's initial work on punctuated equilibrium was coauthored with Niles Eldredge. [20] Gould's model of punctuated equilibrium drew attention to episodic bursts of evolutionary change followed by periods of morphological stability. He challenged the conventional model of gradual, continuous change - called phyletic gradualism. [21]
Group development. The goal of most research on group development is to learn why and how small groups change over time. To quality of the output produced by a group, the type and frequency of its activities, its cohesiveness, the existence of group conflict. A number of theoretical models have been developed to explain how certain groups ...