- Facilitated variation
Facilitated variation is a new theory that has been presented by
Marc W. Kirschner, a professor and chair at the Department of Systems Biology, Harvard Medical School, and John C. Gerhart, a professor at the Graduate School, University of California, Berkeley.
The theory of facilitated variation addresses the nature of variation in evolution. Recent advances in cellular and developmental biology in the light of evolutionary biology sheds light on a number of mechanisms for generating novelty. While the concept and mechanism of natural selection is well understood, the variation component of the evolutionary theory remains under-developed. Variation mechanisms such as mutations, genetic drift, and genetic flow have been studied and documented thoroughly. The theory of facilitated variation is an effort to illustrate that seemingly complex biological systems can arise with a limited number of genes, and a limited number of variation mechanisms.
This is accomplished by exploring the relation between the genotype and phenotype, specifically:
* How are changes in the genotype translated to changes in the phenotype?
* Can environmental conditions affecting the phenotype affect the genotype?
* Since selection operates on the phenotype, how can physiological adaptability affect selection?
The theory can be summarized in the following points:
* Organisms have 'constrained' and 'deconstrained' variations of their phenotype. The constrained processes remain mostly unchanged but they allow 'deconstrained' processes to alter the phenotype without resulting in lethality.
* The constrained elements are called "conserved core processes" that remain in stasis for perhaps millions of years and they endure little if any changes. These core processes, such as the processing of DNA and RNA, are created in rapid 'invention' periods (e.g from prokaryotes to Eukaryotes), and are shared by all organisms.
* The 'deconstrained' processes are those that change the amount, time, kind, and place of gene expression.
* The 'conserved core processes' are linked via weak regulatory linkage, which is a loose mechanism for signal transcription. This mechanism facilitates new changes in how genes are expressed, thereby leading to variations in the phenotype which are selected upon. Furthermore, changes and combinations of these weak permissive signals can give rise to new novel functions on the structural and molecular level.
* Exploratory processes have the ability to generate many different phenotypical outcomes or states given a limited number of genes. A few of these states are selected for their physiological adaptability in their respective environmental conditions. For example, the vascular system expands to regions with insufficient oxygen supply. There is no predetermined genetical map for the distribution of blood vessels in the body, but the vascular system responds to signals from hypoxic tissues. Exploratory processes are powerful because they provide organisms with a tremendous adaptation scope.
In the classical Darwinian view, a large number of successive mutations, each selected for its usefulness to the survival of the organism, is required to produce novel structures such as wings, limbs, or the brain. Alternatively, facilitated variation asserts that the physiological adaptability of core processes and properties such as weak linkage and exploratory processes enable proteins, cells, and body structures to interact in numerous ways that can lead to the creation of novelty with a limited number of genes, and a limited number of mutations.
Therefore, the role of mutations is often to change how, where, and when the genes are expressed during the development of the embryo and adult.
The theory challenges
Irreducible complexityby explaining how mutationcan cause unusual changes within a species. They explain how the individual organism can change from a passive target of natural selection, to a central player in the 3-billion-year history of evolution. By closing the major gap in Darwin’s theory Kirschner and Gerhart also provide a timely scientific rebuttal to modern critics of evolution who champion " intelligent design".
*Marc W. Kirschner, John C. Gerhart: "The Plausibility of Life: Resolving Darwin's Dilemma" (
Yale University Press 2005) ISBN 0-300-10865-6, released in 2005.
* [http://yalepress.yale.edu/yupbooks/book.asp?isbn=0300108656 The Plausibility of Life]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Erleichterte Variation — Die Theorie der erleichterten Variation (engl: Theory of Facilitated Variation) ist ein Erklärungsmodell, das sich als Ergänzung der Evolutionstheorie versteht und sich mit der Beschaffenheit der Variation in der Evolution befasst. Diese Theorie… … Deutsch Wikipedia
Evolutionäre Entwicklungsbiologie — Die evolutionäre Entwicklungsbiologie oder kurz Evo Devo (abgeleitet vom englischen Begriff evolutionary developmental biology) ist eine Forschungsrichtung der Biologie, die untersucht, wie die Systeme der Individualentwicklung (Ontogenese) der… … Deutsch Wikipedia
Orthogenesis — Orthogenesis, orthogenetic evolution, progressive evolution or autogenesis, is the hypothesis that life has an innate tendency to evolve in a unilinear fashion due to some internal or external driving force . The hypothesis is based on… … Wikipedia
Irreducible complexity — This article covers irreducible complexity as used by those who argue for intelligent design. For information on irreducible complexity as used in Systems Theory, see Irreducible complexity (Emergence). Irreducible complexity (IC) is an argument… … Wikipedia
Marc Kirschner — ist ein US amerikanischer Biologe. Beruflicher Werdegang Kirschner graduierte 1966 an der Northwestern University und erreichte 1971 seinen Doktor an der University of California, Berkeley. 1972 wurde er Assistant Professor an der Prince … Deutsch Wikipedia
Complexite irreductible — Complexité irréductible Cet article traite de la complexité irréductible telle qu elle est utilisée par les partisans du dessein intelligent ((en) intelligent design). Pour la complexité irréductible dans le cadre de la théorie des systèmes … Wikipédia en Français
Complexité Irréductible — Cet article traite de la complexité irréductible telle qu elle est utilisée par les partisans du dessein intelligent ((en) intelligent design). Pour la complexité irréductible dans le cadre de la théorie des systèmes, voir l article… … Wikipédia en Français
Collaborative intelligence — is a term used in several disciplines, and has several different meanings. In a business setting, it can describe the result of accessing a network of people. It is also used to denote non anonymous heterogeneity in multi agent problem solving… … Wikipedia
France — /frans, frahns/; Fr. /frddahonns/, n. 1. Anatole /ann nann tawl /, (Jacques Anatole Thibault), 1844 1924, French novelist and essayist: Nobel prize 1921. 2. a republic in W Europe. 58,470,421; 212,736 sq. mi. (550,985 sq. km). Cap.: Paris. 3.… … Universalium
Europe, history of — Introduction history of European peoples and cultures from prehistoric times to the present. Europe is a more ambiguous term than most geographic expressions. Its etymology is doubtful, as is the physical extent of the area it designates.… … Universalium