"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]
Genetic drift is the change in the frequency of an existing gene variant (allele) in a population due to random sampling of organisms. The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces. A population's allele frequency is the fraction of the copies of one gene that share a particular form.
Molecular evolution is the process of change in the sequence composition of cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and population genetics to explain patterns in these changes. Major topics in molecular evolution concern the rates and impacts of single nucleotide changes, neutral evolution vs. natural selection, origins of new genes, the genetic nature of complex traits, the genetic basis of speciation, evolution of development, and ways that evolutionary forces influence genomic and phenotypic changes.
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. The neutral theory allows for the possibility that most mutations are deleterious, but holds that because these are rapidly removed by natural selection, they do not make significant contributions to variation within and between species at the molecular level. A neutral mutation is one that does not affect an organism's ability to survive and reproduce. The neutral theory assumes that most mutations that are not deleterious are neutral rather than beneficial. Because only a fraction of gametes are sampled in each generation of a species, the neutral theory suggests that a mutant allele can arise within a population and reach fixation by chance, rather than by selective advantage.
Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.
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 working on population genetics/molecular evolution. She and Richard Lewontin were jointly awarded the Crafoord Prize for 2015 "for their pioneering analyses and fundamental contributions to the understanding of genetic polymorphism".
In evolutionary biology, conserved sequences are identical or similar sequences in nucleic acids or proteins across species, or within a genome, or between donor and receptor taxa. Conservation indicates that a sequence has been maintained by natural selection.
Genetic hitchhiking, also called genetic draft or the hitchhiking effect, is when an allele changes frequency not because it itself is under natural selection, but because it is near another gene that is undergoing a selective sweep and that is on the same DNA chain. When one gene goes through a selective sweep, any other nearby polymorphisms that are in linkage disequilibrium will tend to change their allele frequencies too. Selective sweeps happen when newly appeared mutations are advantageous and increase in frequency. Neutral or even slightly deleterious alleles that happen to be close by on the chromosome 'hitchhike' along with the sweep. In contrast, effects on a neutral locus due to linkage disequilibrium with newly appeared deleterious mutations are called background selection. Both genetic hitchhiking and background selection are stochastic (random) evolutionary forces, like genetic drift.
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 either be lost or will replace all other alleles of the gene. This 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.
Masatoshi Nei is a Japanese-born American evolutionary biologist currently affiliated with the Department of Biology at Temple University as a Carnell Professor. He was, until recently, Evan Pugh Professor of Biology at Pennsylvania State University and Director of the Institute of Molecular Evolutionary Genetics; he was there from 1990 to 2015.
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. In the absence of mutation or heterozygote advantage, any allele must eventually be lost completely from the population or fixed. 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).
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-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 fixed allele is an allele that is the only variant that exists for that gene in all the population. A fixed allele is homozygous for all members of the population. The term allele normally refers to one variant gene out of several possible for a particular locus in the DNA. When all but one allele go extinct and only one remains, that allele is said to be fixed.
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.
