Punctuated equilibria: an alternative to phyletic gradualism
01 Jan 1972-
About: The article was published on 1972-01-01 and is currently open access. It has received 2655 citations till now. The article focuses on the topics: Phyletic gradualism & Punctuated gradualism.
Citations
More filters
TL;DR: This poster presents a probabilistic procedure to characterize the response of the immune system to E.coli bacteria and shows clear patterns in response to the presence of E. coli.
Abstract: 1Department of Genetics, University of Georgia, Athens, Georgia 30602; 2NMFS/ CZES, Genetics, 2725 Montlake Boulevard East, Seattle, Washington 98112; 3Savannah River Ecology Laboratory, Drawer E, Aiken, South Carolina 29801; ~Department of Microbiology and Immunology, School of Medicine, University of California, Los Angeles, California 90024; -SSchool f Veterinary Medicine, Virginia Tech University, Blacksburg, Virginia 24046
3,366 citations
TL;DR: It is argued that virtually none of the examples brought forward to refute the model of punctuated equilibria can stand as support for phyletic gradualism; many are so weak and ambiguous that they only reflect the persistent bias for gradualism still deeply embedded in paleontological thought.
Abstract: We believe that punctuational change dominates the history of life: evolution is concentrated in very rapid events of speciation (geologically instantaneous, even if tolerably continuous in ecological time). Most species, during their geological history, either do not change in any appreciable way, or else they fluctuate mildly in morphology, with no apparent direction. Phyletic gradualism is very rare and too slow, in any case, to produce the major events of evolution. Evolutionary trends are not the product of slow, directional transformation within lineages; they represent the differential success of certain species within a clade—speciation may be random with respect to the direction of a trend (Wright's rule).As an a priori bias, phyletic gradualism has precluded any fair assessment of evolutionary tempos and modes. It could not be refuted by empirical catalogues constructed in its light because it excluded contrary information as the artificial result of an imperfect fossil record. With the model of punctuated equilibria, an unbiased distribution of evolutionary tempos can be established by treating stasis as data and by recording the pattern of change for all species in an assemblage. This distribution of tempos can lead to strong inferences about modes. If, as we predict, the punctuational tempo is prevalent, then speciation—not phyletic evolution—must be the dominant mode of evolution.We argue that virtually none of the examples brought forward to refute our model can stand as support for phyletic gradualism; many are so weak and ambiguous that they only reflect the persistent bias for gradualism still deeply embedded in paleontological thought. Of the few stronger cases, we concentrate on Gingerich's data for Hyopsodus and argue that it provides an excellent example of species selection under our model. We then review the data of several studies that have supported our model since we published it five years ago. The record of human evolution seems to provide a particularly good example: no gradualism has been detected within any hominid taxon, and many are long-ranging; the trend to larger brains arises from differential success of essentially static taxa. The data of molecular genetics support our assumption that large genetic changes often accompany the process of speciation.Phyletic gradualism was an a priori assertion from the start—it was never “seen” in the rocks; it expressed the cultural and political biases of 19th century liberalism. Huxley advised Darwin to eschew it as an “unnecessary difficulty.” We think that it has now become an empirical fallacy. A punctuational view of change may have wide validity at all levels of evolutionary processes. At the very least, it deserves consideration as an alternate way of interpreting the history of life.
2,278 citations
TL;DR: In this paper, a study of the complete life-spans of eight naturally-ocurring teams was conducted and it was found that several project groups did not accomplish their work by progressing gradually through a universal series of stages, as traditional group development models would predict.
Abstract: This study of the complete life-spans of eight naturally-ocurring teams began with the unexpected finding that several project groups, studied for another purpose, did not accomplish their work by progressing gradually through a universal series of stages, as traditional group development models would predict. Instead, teams progressed in a pattern of “punctuated equilibrium,” through alternating inertia and revolution in the behaviors and themes through which they approached their work. The findings also suggested that groups' progress was triggered more by members' awareness of time and deadlines than by completion of an absolute amount of work in a specific developmental stage. The paper proposes a new model of group development that encompasses the timing and mechanisms of change as well as groups' dynamic relations with their contexts. Implications for theory, research, and practice are drawn.
2,269 citations
TL;DR: The African Middle and early Late Pleistocene hominid fossil record is fairly continuous and in it can be recognized a number of probably distinct species that provide plausible ancestors for H. sapiens, and suggests a gradual assembling of the package of modern human behaviors in Africa, and its later export to other regions of the Old World.
2,165 citations
TL;DR: Models from six domains are compared to explicate the punctuated equilibrium paradigm and show its broad applicability for organizational studies: how it is triggered, how systems function during such periods, and how it concludes.
Abstract: Research on how organizational systems develop and change is shaped, at every level of analysis, by traditional assumptions about how change works. New theories in several fields are challenging some of the most pervasive of these assumptions, by conceptualizing change as a punctuated equilibrium: an alternation between long periods when stable infrastructures permit only incremental adaptations, and brief periods of revolutionary upheaval. This article compares models from six domains—adult, group, and organizational development, history of science, biological evolution, and physical science—to explicate the punctuated equilibrium paradigm and show its broad applicability for organizational studies. Models are juxtaposed to generate new research questions about revolutionary change in organizational settings: how it is triggered, how systems function during such periods, and how it concludes. The article closes with implications for research and theory.
2,033 citations