Gene-centered view of evolution

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The gene-centered view of evolution, gene selection theory or selfish gene theory holds that natural selection acts primarily through differential survival of competing genes, increasing the frequency of those alleles whose phenotypic effects successfully promote their own propagation. According to this theory, adaptations are the phenotypic effects through which genes achieve their propagation.

Introduction

The gene-centered view of evolution is a different way of looking at the basis of evolutionary development. It turns the whole solution of evolution inside-out for the purpose of examination. What this new perspective reveals is a more easily understood model for the evolution of social characteristics such as racism, deceit and kindness that much of the study of evolution, caught up in the survival of the fittest individual organisms, overlooks. Moreover, it eases the transition to the evolutionary modeling of other mediums such as the development of new technologies and the changes in Wikipedia pages, because it describes evolution in terms of the evolution of specific features as opposed to just in terms of the features’ vehicles.

Acquired characteristics are not inherited

Discoveries in science such as the formulation of the central dogma of molecular biology made it clear that the inheritance of acquired characters was not an evolutionary factor in a physical sense and identified genes as lasting entities that survive through many generations. Maynard Smith summarized the issue:

The rejection of the inheritance of acquired characters combined with the classical mathematical evolutionary biology developed by Ronald Fisher (particularly in his 1930 book, The Genetical Theory of Natural Selection), J. B. S. Haldane and Sewall Wright, they paved the way to the formulation of the selfish gene theory.^{[clarification needed]} An exception to this of course is the advent of society, where adaptations are indeed passed on through generations, and can even influence which members are allowed to prosper and reproduce, eventually effecting change in the genetic makeup of the population. For cases when environment can influence heredity see epigenetics.^{[clarification needed]}

Gene as the primary unit of selection

The 1976 book The Selfish Gene by Richard Dawkins was a notable early work of popular science that focused on the gene-centered view of evolution.

The view of the gene as the unit of selection was developed mainly in the books Adaptation and Natural Selection (1966), by George C. Williams, and in The Selfish Gene (1976) and The Extended Phenotype (1982), both by Richard Dawkins. It had earlier been proposed by Colin Pittendrigh in his 1958 article, Adaptation, natural selection, and behavior, and in the classic papers about altruism of 1963 and 1964 by William Hamilton.

According to Williams' 1966 book:

Williams argued that "The natural selection of phenotypes cannot in itself produce cumulative change, because phenotypes are extremely temporary manifestations." (Williams, 1966) Each phenotype is the unique product of the interaction between genome and environment. It does not matter how fit and fertile a phenotype is, it will eventually be destroyed and will never be duplicated.

Since 1954, it has been known that DNA is the main physical substrate to genetic information, and it is capable of high fidelity replication through many generations. So, a particular sequence of DNA can have a high permanence and a low rate of endogenous change.

In normal sexual reproduction, an entire genome is the unique combination of father's and mother's chromosomes produced at the moment of fertilization. It is generally destroyed with its organism, because "meiosis and recombination destroy genotypes as surely as death." (Williams, 1966) Only half of it is transmitted to each descendant due to the independent segregation.

The gene as an informational entity persists for an evolutionary significant span of time through a lineage of many physical copies.

In his book River out of Eden, Dawkins coins the phrase God's utility function to explain his view on genes as units of selection. He uses this phrase as a synonym of the "meaning of life" or the "purpose of life". By rephrasing the word purpose in terms of what economists call a utility function, meaning "that which is maximized", Dawkins attempts to reverse-engineer the purpose in the mind of the Divine Engineer of Nature, or the Utility Function of God. Finally, Dawkins argues that it is a mistake to assume that an ecosystem or a species as a whole exists for a purpose. He writes that it is incorrect to suppose that individual organisms lead a meaningful life either; in nature, only genes have a utility function – to perpetuate their own existence with indifference to great sufferings inflicted upon the organisms they build, exploit and discard.

Organisms as Vehicles

Genes are not naked in the world. They are usually packed together inside a genome, which is itself contained inside an organism. Genes group together into genomes because "genetic replication makes use of energy and substrates that are supplied by the metabolic economy in much greater quantities than would be possible without a genetic division of labour" (Haig, 1997). They build vehicles to promote their mutual interests of jumping into the next generation of vehicles. As Dawkins puts it, organisms are the "survival machines" of genes.

The phenotypic effect of a particular gene is contingent on its environment, including the fellow genes constituting with it the total genome. A gene never has a fixed effect, so how is it possible to speak of a gene for long legs? It is because of the phenotypic differences between alleles. One may say that one allele, all other things being equal or varying within certain limits, causes greater legs than its alternative. This difference enables the scrutiny of natural selection.

"A gene can have multiple phenotypic effects, each of which may be of positive, negative or neutral value. It is the net selective value of a gene's phenotypic effect that determines the fate of the gene" (Cronin, 1991). For instance, a gene can cause its bearer to have greater reproductive success at a young age, but also cause a greater likelihood of death at a later age. If the benefit outweighs the harm, averaged out over the individuals and environments in which the gene happens to occur, then phenotypes containing the gene will generally be positively selected and thus the abundance of that gene in the population will increase.

Even so, it becomes necessary to model the genes in combination with their vehicle as well as in combination with the vehicle’s environment.

Selfish Gene Theory

The selfish gene theory of natural selection can be restated as follows:

The result is that "the prevalent genes in a sexual population must be those that, as a mean condition, through a large number of genotypes in a large number of situations, have had the most favourable phenotypic effects for their own replication." (Williams, 1985) In other words, we expect selfish genes, "selfish" meaning that promotes its own survival without necessarily promoting the survival of the organism, group or even species. This theory implicates that adaptations are the phenotypic effects of genes to maximize their representation in the future generations. An adaptation is maintained by selection if it promotes genetic survival directly or some subordinate goal that ultimately contributes to successful reproduction.

Individual altruism, genetic egoism

The gene is a unit of hereditary information that exists in many physical copies in the world, and which particular physical copy will be replicated and originate new copies does not matter from the gene's point of view. (Williams, 1992) A selfish gene could be favoured by selection by producing altruism among organisms containing it. The idea is summarized as follows:

A gene in a somatic cell of an individual may forego replication to promote the transmission of its copies in the germ line cells. It ensures the high value of p = 1 due to their constant contact and their common origin from the zygote.

The kin selection theory predicts that a gene may promote the recognition of kinship by historical continuity: a mammalian mother learns to identify her own offspring in the act of giving birth; a male preferentially directs resources to the offspring of mothers with whom he has copulated; the other chicks in a nest are siblings; and so on. The expected altruism between kin is calibrated by the value of p, also known as the coefficient of relatedness. For instance, an individual have a p = 1/2 in relation to his brother, and p = 1/8 to his cousin, so we would expect, ceteris paribus, greater altruism among brothers than among cousins. Geneticist J.B.S. Haldane is famously quoted, "Would I lay down my life to save my brother? No, but I would to save two brothers or eight cousins." ^[1] Don't worry, he was only joking. The slight horror that such a statement invokes suggests that there is something else at work. Examining the human propensity for altruism, kin selection theory seems like a vast underestimate for cross-familiar, cross-racial, and even cross-special acts of kindness. A far more expansive explanation for altruism is rooted in the green-beard effect.

Green-beard effect

Green-beard effects gained their name from a thought-experiment of Richard Dawkins (1976), who considered the possibility of a gene that caused its possessors to develop a green beard and to be nice to other green-bearded individuals. Since then, a 'green beard effect' has come to refer to forms of genetic self-recognition in which a gene in one individual might direct benefits to other individuals that possess the gene.

Such genes are essentially especially selfish, benefiting themselves regardless of the fates of their vehicles.

Note that because the green-beard effect depends on the ability of the individual to recognize the mirrored trait in other individuals, green-beard effects are most prevalent in organisms with sufficiently great intellects. Creatures of great intellect, such as humans, are capable of evolving culturally as well as genetically. Thus, insomuch as culture varies from our genes, the surface changeable adaptations of culture may magnify any underlying genetic green-bearding.

All kinds of altruism

Kindness

On the other hand, a single trait, group reciprocal kindness, is capable of explaining the vast majority of altruism that is generally accepted as “good” by modern societies. Imagine a green-bearding behavioral trait whose recognition does not depend on the recognition of some external feature such as beard color, but relies on recognition of the behavior itself. Imagine now that the behavior is altruistic. The success of such a trait in sufficiently intelligent and undeceived organisms is implicit. Moreover, the existence of such a trait predicts a tendency for kindness to unrelated organisms that are apparently kind, even if the organisms are of a completely different species. Moreover, the gene need not be exactly the same, so long as the effect is similar. Multiple versions of the gene—or even meme—would have virtually the same effect in a sort of symbiotic green-bearding cycle of altruism.

Deceit

Whenever recognition plays a role in evolution, so does deception. Just like the harmless lizard that has evolved a pattern that mimics its poisonous cousin and trick predators, the selfish creature may pretend to be kind by “growing a green beard” whatever that green beard may be. Thus green-bearding and the selfish gene theory also give rise to an explanation for the evolution of lies and deceit, characteristics that do not benefit the population as a whole.

Intragenomic conflict

As genes are capable of producing individual altruism, they are capable of producing conflict among genes inside the genome of one individual. This phenomenon was called intragenomic conflict and arises when one gene promotes its own replication in detriment to other genes in the genome. The classic example is segregation distorter genes that cheat during meiosis or gametogenesis and end up in more than half of the functional gametes. These genes persist even resulting in reduced fertility. Egbert Leigh (1971) compared the genome to "a parliament of genes: each acts in its own self-interest, but if its acts hurt the others, they will combine together to suppress it" to explain the relative low occurrence of intragenomic conflict. This may be a confusing explanation as the genes themselves are limited to their natural actions and cannot in general act to suppress problematic genes. Such explanations may give rise to criticisms of oversimplification. A better description may be the application of group selection to genomic conflict modeling.

Challenges to the gene-centric view

Prominent opponents of this gene-centric view of evolution include evolutionary biologist Ernst Mayr, palaeontologist Stephen Jay Gould, biologist and anthropologist David Sloan Wilson and philosopher Elliot Sober.

Mayr went so far as to say "Dawkins' basic theory of the gene being the object of evolution is totally non-Darwinian".^[2]

Writing in the New York Review of Books, Gould has characterized the gene-centered perspective as confusing book-keeping with causality. Gould views selection as working on many levels, and has called attention to a hierarchical perspective of selection. Gould also called the claims on Selfish Gene "strict adaptationism", "ultra-Darwinism", and "Darwinian fundamentalism", describing them as excessively "reductionist". He saw the theory as leading to a simplistic "algorithmic" theory of evolution, or even to the re-introduction of a teleological principle.^[3]

Gould also addressed the issue of selfish genes in his essay 'Caring groups and selfish genes'.^[4] Gould acknowledged that Dawkins was not imputing conscious action to genes, but simply using shorthand metaphor commonly found in evolutionary writings. To Gould, the fatal flaw was that "no matter how much power Dawkins wishes to assign to genes, there is one thing that he cannot give them - direct visibility to natural selection" (Gould, 1990. p. 76).^[4] Rather, the unit of selection is the phenotype, not the genotype, because it is phenotypes which interact with the environment at the natural selection interface. So, in Kim Sterelny's (2007, p. 83)^[5] summation of Gould's view: "gene differences do not cause evolutionary changes in populations, they register those changes". Sterelny's book provides one of the single best, balanced overviews of the two schools of evolutionary thought represented by Dawkins and Gould.

Since Gould's death in 2002, Niles Eldredge (2004)^[6] has continued with counter-arguments to gene-centered natural selection. Eldredge notes that in Dawkin's book A Devil's Chaplain, which was published just before Eldrege's book, "Richard Dawkins comments on what he sees as the main difference between his position and that of the late Stephen Jay Gould. He concludes that it is his own vision that genes play a causal role in evolution", while Gould (and Eldredge) "sees genes as passive recorders of what worked better than what" (p. 233).

Critics of the gene-centred view of evolution approach suggest that taking the gene as the unit of selection − of a single event in which an individual either succeeds or fails to reproduce − is misleading, but that the gene could be better described as a unit of evolution − of the long-term changes in allele frequencies in a population.^[7] Another common objection is that genes cannot survive alone, but must cooperate to build an individual, and therefore cannot be an independent "unit".^[8] Advocates for higher levels of selection such as Richard Lewontin, David Sloan Wilson, and Elliot Sober suggest that there are many phenomena (including altruism) that gene-based selection cannot satisfactorily explain.

Summary

The gene-centered view of evolution is a synthesis of the theory of evolution by natural selection, the particulate inheritance theory and the non-transmission of acquired characters. It states that those genes whose phenotypic effects successfully promote their own propagation will be favourably selected in detriment to their competitors. This process produces adaptations for the benefit of genes that promote the reproductive success of the organism, or of other organisms containing the same gene (kin altruism and green-beard effects), or even only its own propagation in detriment to the other genes of the genome (intragenomic conflict).^{[citation needed]}

Other main figures

Besides Richard Dawkins and George C. Williams, other biologists and philosophers have expanded and refined the selfish gene theory, such as John Maynard Smith, Robert Trivers, David Haig, Helena Cronin, David Hull, Philip Kitcher and Daniel Dennett.

See also

Evolutionary biology portal

• Evolutionary biology

Bibliography

• Crick, F. (1970) Central dogma of molecular biology Nature 227 (August 8): 561-563.
• Cronin, H. (1991) The Ant and the Peacock. Cambridge University Press, Cambridge. ISBN 0-521-32937-X
• Darwin, C. & Wallace, A. (1858) On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection. Proceedings of Linnean Society 3 (July): 45-62.
• Dawkins, R. (1976) The Selfish Gene. Oxford University Press, Oxford. ISBN 0-19-286092-5
• Dawkins, R. (1982) The Extended Phenotype. Oxford University Press, Oxford. ISBN 0-19-288051-9
• Dawkins, R. (1982) "Replicators and Vehicles" King's College Sociobiology Group, eds., Current Problems in Sociobiology, Cambridge, Cambridge University Press, pp. 45–64.
• Fisher, R. A. (1930) The Genetical Theory of Natural Selection. Oxford University Press, Oxford. ISBN 0-19-850440-3.
• Haig, D. (1997) The Social Gene. In J. R. Krebs and N. B. Davies, eds., Behavioural Ecology, Oxford: Blackwell Scientific, pp. 284–304.
• Hamilton, W. D. (1963) The evolution of altruistic behavior. The American Naturalist 97 (896): 354-356.
• Hamilton, W. D. (1964) The genetical evolution of social behaviour. Journal of Theoretical Biology 7: 1-52.
• Leigh, E. (1971) Adaptation and Diversity. Cooper, San Francisco.
• Maynard Smith, J. (1998) Evolutionary Genetics: 2nd Edition. Oxford University Press, Oxford.
• Mayr, E. (1997) The objects of selection Proc. Natl. Acad. Sci. USA 94 (March): 2091-2094.
• Pittendrigh, C. (1958) Adaptation, natural selection, and behavior. In A. Roe and G. G. Simpson, eds., Behavior and Evolution, New Haven: Yale University Press, pp 390–416.
• Williams, G. C. (1966) Adaptation and Natural Selection. Princeton University Press, Princeton. ISBN 0-691-02615-7
• Williams, G. C. (1985) A defense of reductionism in evolutionary biology. Oxford Surveys in Evolutionary Biology, 2: 1-27.
• Williams, G. C. (1992) Natural Selection: Domains, Levels and Challenges. Oxford University Press, Oxford. ISBN 0-19-506932-3