"Non-Darwinian Evolution" is a scientific paper written by Jack Lester King and Thomas H. Jukes and published in 1969. It is credited, along with Motoo Kimura's 1968 paper "Evolutionary Rate at the Molecular Level", with proposing what became known as the neutral theory of molecular evolution. The paper brings together a wide variety of evidence, ranging from protein sequence comparisons to studies of the Treffers mutator gene[1] in E. coli to analysis of the genetic code to comparative immunology, to argue that most protein evolution is due to neutral mutations and genetic drift. It was published in the journal Science on May 16, 1969.[2]
The idea of evolution at the molecular level being driven by the random processes of mutation and genetic drift, largely independent from natural selection, was controversial at the time; the provocative title further emphasized the break with mainstream evolutionary thought, which was dominated by the synthetic theory of evolution, often referred to as "Neo-Darwinism". Although they argued for essentially the same conclusion as Motoo Kimura's earlier paper, King and Jukes criticized one of Kimura's central arguments, an estimate of the rate of amino acid change in proteins that according to Kimura would indicate an impossibly high genetic load if the changes were caused by natural selection. The paper was initially rejected by its reviewers (one thought it was trivial and the other thought it was totally wrong ), but was published after an appeal. This time, the reviewer was James F. Crow, Motoo Kimura's collaborator. Despite the intentionally inflammatory title and "antiauthoritarian tone"—which according to historian Michael R. Dietrich "undoubtedly struck a nerve", especially since King and Jukes worked at UC Berkeley during that period of political unrest—the paper acknowledges the significance of natural selection; it merely argues against panselectionism (as advocated at the molecular level by G. G. Simpson and Emil L. Smith in particular). From 1969 until the early 1970s, the concept of neutral mutations driven to fixation by genetic drift was known as "Non-Darwinian Evolution"; it was subsequently termed the "neutral theory of molecular evolution".[3]
"Non-Darwinian Evolution" generated considerable interest in neutral mutations, and became very influential in the field of molecular evolution. The response by critics (including direct rebuttals by Bryan Clarke[4] and Rollin Richmond[5]), and subsequent replies (by King and Jukes, Kimura, and others), marked the beginning of the neutralist/selectionist controversy. In the 1970s and 1980s, Kimura became the chief advocate of the neutral theory, but he adopted a number of King and Jukes' arguments and de-emphasized genetic load.[3]
1 2 Dietrich, Michael R. (1994-03-01). "The origins of the neutral theory of molecular evolution". Journal of the History of Biology. 27 (1): 21–59. doi:10.1007/BF01058626. PMID11639258. S2CID367102.
Junk DNA is a DNA sequence that has no known biological function. Most organisms have some junk DNA in their genomes—mostly, pseudogenes and fragments of transposons and viruses—but it is possible that some organisms have substantial amounts of junk DNA.
Genetic drift, also known as random genetic drift, allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance.
Molecular evolution describes how inherited DNA and/or RNA change over evolutionary time, and the consequences of this for proteins and other components of cells and organisms. Molecular evolution is the basis of phylogenetic approaches to describing the tree of life. Molecular evolution overlaps with population genetics, especially on shorter timescales. Topics in molecular evolution include the origins of new genes, the genetic nature of complex traits, the genetic basis of adaptation and speciation, the evolution of development, and patterns and processes underlying genomic changes during evolution.
The neutral theory of molecular evolution holds that most evolutionary changes occur at the molecular level, and most of the variation within and between species are due to random genetic drift of mutant alleles that are selectively neutral. The theory applies only for evolution at the molecular level, and is compatible with phenotypic evolution being shaped by natural selection as postulated by Charles Darwin.
Population genetics is a subfield of genetics that deals with genetic differences within and among populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.
The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleotide sequences for DNA, RNA, or amino acid sequences for proteins.
Motoo Kimura was a Japanese biologist best known for introducing the neutral theory of molecular evolution in 1968. He became one of the most influential theoretical population geneticists. He is remembered in genetics for his innovative use of diffusion equations to calculate the probability of fixation of beneficial, deleterious, or neutral alleles. Combining theoretical population genetics with molecular evolution data, he also developed the neutral theory of molecular evolution in which genetic drift is the main force changing allele frequencies. James F. Crow, himself a renowned population geneticist, considered Kimura to be one of the two greatest evolutionary geneticists, along with Gustave Malécot, after the great trio of the modern synthesis, Ronald Fisher, J. B. S. Haldane, and Sewall Wright.
Tomoko Ohta is a Japanese scientist and Professor Emeritus of the National Institute of Genetics. Ohta works on population genetics/molecular evolution and is known for developing the nearly neutral theory of evolution.
Genetic distance is a measure of the genetic divergence between species or between populations within a species, whether the distance measures time from common ancestor or degree of differentiation. Populations with many similar alleles have small genetic distances. This indicates that they are closely related and have a recent common ancestor.
The Neutral Theory of Molecular Evolution is an influential monograph written in 1983 by Japanese evolutionary biologist Motoo Kimura. While the neutral theory of molecular evolution existed since his article in 1968, Kimura felt the need to write a monograph with up-to-date information and evidences showing the importance of his theory in evolution.
Neutral mutations are changes in DNA sequence that are neither beneficial nor detrimental to the ability of an organism to survive and reproduce. In population genetics, mutations in which natural selection does not affect the spread of the mutation in a species are termed neutral mutations. Neutral mutations that are inheritable and not linked to any genes under selection will be lost or will replace all other alleles of the gene. That loss or fixation of the gene proceeds based on random sampling known as genetic drift. A neutral mutation that is in linkage disequilibrium with other alleles that are under selection may proceed to loss or fixation via genetic hitchhiking and/or background selection.
In population genetics, fixation is the change in a gene pool from a situation where there exists at least two variants of a particular gene (allele) in a given population to a situation where only one of the alleles remains. That is, the allele becomes fixed. In the absence of mutation or heterozygote advantage, any allele must eventually either be lost completely from the population, or fixed, i.e. permanently established at 100% frequency in the population. Whether a gene will ultimately be lost or fixed is dependent on selection coefficients and chance fluctuations in allelic proportions. Fixation can refer to a gene in general or particular nucleotide position in the DNA chain (locus).
The nearly neutral theory of molecular evolution is a modification of the neutral theory of molecular evolution that accounts for the fact that not all mutations are either so deleterious such that they can be ignored, or else neutral. Slightly deleterious mutations are reliably purged only when their selection coefficient are greater than one divided by the effective population size. In larger populations, a higher proportion of mutations exceed this threshold for which genetic drift cannot overpower selection, leading to fewer fixation events and so slower molecular evolution.
Jack Lester King was an American evolutionary biologist best known for co-authoring a seminal paper on the neutral theory of molecular evolution, "Non-Darwinian Evolution".
Thomas Hughes Jukes was a British-born American biologist known for his work in nutrition, molecular evolution, and for his public engagement with controversial scientific issues, including DDT, vitamin C and creationism. He was the co-author, with Jack Lester King, of the 1969 Science article "Non-Darwinian Evolution" which, along with Motoo Kimura's earlier publication, was the origin of the neutral theory of molecular evolution.
The history of molecular evolution starts in the early 20th century with "comparative biochemistry", but the field of molecular evolution came into its own in the 1960s and 1970s, following the rise of molecular biology. The advent of protein sequencing allowed molecular biologists to create phylogenies based on sequence comparison, and to use the differences between homologous sequences as a molecular clock to estimate the time since the last common ancestor. In the late 1960s, the neutral theory of molecular evolution provided a theoretical basis for the molecular clock, though both the clock and the neutral theory were controversial, since most evolutionary biologists held strongly to panselectionism, with natural selection as the only important cause of evolutionary change. After the 1970s, nucleic acid sequencing allowed molecular evolution to reach beyond proteins to highly conserved ribosomal RNA sequences, the foundation of a reconceptualization of the early history of life.
A nonsynonymous substitution is a nucleotide mutation that alters the amino acid sequence of a protein. Nonsynonymous substitutions differ from synonymous substitutions, which do not alter amino acid sequences and are (sometimes) silent mutations. As nonsynonymous substitutions result in a biological change in the organism, they are subject to natural selection.
A neutral network is a set of genes all related by point mutations that have equivalent function or fitness. Each node represents a gene sequence and each line represents the mutation connecting two sequences. Neutral networks can be thought of as high, flat plateaus in a fitness landscape. During neutral evolution, genes can randomly move through neutral networks and traverse regions of sequence space which may have consequences for robustness and evolvability.
The rate of evolution is quantified as the speed of genetic or morphological change in a lineage over a period of time. The speed at which a molecular entity evolves is of considerable interest in evolutionary biology since determining the evolutionary rate is the first step in characterizing its evolution. Calculating rates of evolutionary change is also useful when studying phenotypic changes in phylogenetic comparative biology. In either case, it can be beneficial to consider and compare both genomic data and paleontological data, especially in regards to estimating the timing of divergence events and establishing geological time scales.
Alternatives to Darwinian evolution have been proposed by scholars investigating biology to explain signs of evolution and the relatedness of different groups of living things. The alternatives in question do not deny that evolutionary changes over time are the origin of the diversity of life, nor that the organisms alive today share a common ancestor from the distant past ; rather, they propose alternative mechanisms of evolutionary change over time, arguing against mutations acted on by natural selection as the most important driver of evolutionary change.
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