| Gene-centric View Of Evolution |
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The gene-centric view of evolution, '''gene selection theory''' or '''selfish gene theory''' holds that Natural Selection acts through differential survival of Genes , increasing the frequency of those Allele s whose Phenotypic effects successfully promotes its own Replication at the expense of their less efficient competitors. This view is at odds with the view that selection acts through differential survival of higher units such as Population s and Species ( Group Selection ). HISTORY The gene-centric view of Evolution is a logical extension of the theory of Natural Selection proposed by Charles Darwin and Alfred Russell Wallace in the light of the discoveries about the mechanisms of Inheritance and development. Gregor Mendel 's particulate inheritance theory, August Weismann 's continuity of the germ plasm, and Francis Crick 's Central Dogma Of Molecular Biology identified genes codified in DNA molecules as (1) the persistent entities that are transmitted through generations and (2) as causal agents of the phenotype. This view was implicit in the Mathematic al evolutionary Biology of the early 20th Century developed by Ronald Fisher (particularly in his 1930 book, '' The Genetical Theory Of Natural Selection ''), J. B. S. Haldane and others, and also in the Kin Selection theory by W.D. Hamilton . Leading up to the 1960s, verbal arguments were often couched in terms of "survival of the species" — essentially Group Selection (a view notably expounded by V.C. Wynne-Edwards ). However, models of the period showed that group selection was severely limited in its strength. As a reaction to this tendency to invoke group selection, George C. Williams and Richard Dawkins sought to advocate a gene centric view in their respective books '' Adaptation And Natural Selection '' and '' The Selfish Gene '', and bring the focus of evolutionary biology back to the gene. Other main figures that developed the gene-centric view of evolution were John Maynard Smith , Robert Trivers , David Haig , David Hull and Daniel C. Dennett . On the sidelines of this conflict, an extended argument developed between Stephen Jay Gould and Dawkins, mostly focused on the semantic issue of whether the individual or the gene is the "unit of selection." Gould insisted that only individuals could reproduce or die, and hence genes could not be the unit of selection. The argument generated a considerable amount of public interest and the many books written by the two authors became bestsellers. A DEFENSE The gene-centric view is based on some simple facts about inheritance and development: First, genes are the hereditary information coded on the base pair sequences of DNA molecules. Genes do two important things: they are replicated and they exert phenotypic effects through RNA and proteins coded by them. Second, genes are the only replicators in biological systems. So, only genetic mutations are transmitted through generations, and phenotypic differences can have long-term impact only if they are produced by genetic differences. Third, genes are the only entities that persist for an evolutionary significant time and exist in many copies. An Organism is the unique product of the interaction between genome and environment (see Gene-environment Interaction ). A sexual Genome is the unique combination of father's and mother's chromosomes and only half of it is transmitted to descendants due to the Independent Segregation . A Chromosome is the unique combination of homologues' fragments and only fragments of it are transmitted to descendants due to Recombination . GENETIC DETERMINISM The gene-centric view is not associated with Genetic Determinism : the phenotype is the joint product of genes and environment. This view only states that phenotypic variation can only be relevant to natural selection if it is anchored on a genetic variation. In other words, if a phenotypic novelty is to be transmited, it can do so only through genes. ADAPTATION Adaptation refers to those phenotypic traits of living systems characterized by their improbable Functional Organization . The Human Hand , the veins' Valves , the Vertebrate Eye , the Hemoglobin Molecule , the Pony Fish 's glow, Parental Investment and Kin Altruism are notorious examples of adaptation. The gene-centric view advocates that all adaptations evolved by natural selection because they caused the transmission of the relevant alleles in a more efficient way. So, all adaptations are for the good of the gene. It is interesting that the first use of the selfish gene metaphor was in explaining how Altruism could evolve by natural selection. Hamilton proposed the theory of Kin Selection , in which a gene could be favorably selected by causing its bearers to be altruistic to other organisms containing copies of it. Kin selection, however, has occasionally been criticised for being essentially a Group Selection argument. CONCLUSION The gene-centric view is the updated version of the theory of natural selection and is more far-reaching than the classic individual-centric view. It explains not only those adaptations that promotes individual reproductive success, but also the adaptations that promote the reproductive success of relatives ( Kin Selection ), Intragenomic Conflict and Green-beard Effect genes. BIBLIOGRAPHY
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