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Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with artificial selection, which in his view is intentional, whereas natural selection is not.
Selfish genetic elements are genetic segments that can enhance their own transmission at the expense of other genes in the genome, even if this has no positive or a net negative effect on organismal fitness. Genomes have traditionally been viewed as cohesive units, with genes acting together to improve the fitness of the organism. However, when genes have some control over their own transmission, the rules can change, and so just like all social groups, genomes are vulnerable to selfish behaviour by their parts.
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 among populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.
In evolutionary genetics, Muller's ratchet is a process through which, in the absence of recombination, an accumulation of irreversible deleterious mutations results. This happens due to the fact that in the absence of recombination, and assuming reverse mutations are rare, offspring bear at least as much mutational load as their parents. Muller proposed this mechanism as one reason why sexual reproduction may be favored over asexual reproduction, as sexual organisms benefit from recombination and consequent elimination of deleterious mutations. The negative effect of accumulating irreversible deleterious mutations may not be prevalent in organisms which, while they reproduce asexually, also undergo other forms of recombination. This effect has also been observed in those regions of the genomes of sexual organisms that do not undergo recombination.
Evolutionary biology is the subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth. It is also defined as the study of the history of life forms on Earth. Evolution holds that all species are related and gradually change over generations. In a population, the genetic variations affect the phenotypes of an organism. These changes in the phenotypes will be an advantage to some organisms, which will then be passed onto their offspring. Some examples of evolution in species over many generations are the peppered moth and flightless birds. In the 1930s, the discipline of evolutionary biology emerged through what Julian Huxley called the modern synthesis of understanding, from previously unrelated fields of biological research, such as genetics and ecology, systematics, and paleontology.
In biology, polymorphism is the occurrence of two or more clearly different morphs or forms, also referred to as alternative phenotypes, in the population of a species. To be classified as such, morphs must occupy the same habitat at the same time and belong to a panmictic population.
Sexual reproduction is an adaptive feature which is common to almost all multicellular organisms and various unicellular organisms, with some organisms being incapable of asexual reproduction. Currently the adaptive advantage of sexual reproduction is widely regarded as a major unsolved problem in biology. As discussed below, one prominent theory is that sex evolved as an efficient mechanism for producing variation, and this had the advantage of enabling organisms to adapt to changing environments. Another prominent theory, also discussed below, is that a primary advantage of outcrossing sex is the masking of the expression of deleterious mutations. Additional theories concerning the adaptive advantage of sex are also discussed below. Sex does, however, come with a cost. In reproducing asexually, no time nor energy needs to be expended in choosing a mate. And if the environment has not changed, then there may be little reason for variation, as the organism may already be well adapted. Sex also halves the amount of offspring a given population is able to produce. Sex, however, has evolved as the most prolific means of species branching into the tree of life. Diversification into the phylogenetic tree happens much more rapidly via sexual reproduction than it does by way of asexual reproduction.
Evolutionary ecology lies at the intersection of ecology and evolutionary biology. It approaches the study of ecology in a way that explicitly considers the evolutionary histories of species and the interactions between them. Conversely, it can be seen as an approach to the study of evolution that incorporates an understanding of the interactions between the species under consideration. The main subfields of evolutionary ecology are life history evolution, sociobiology, the evolution of interspecific interactions and the evolution of biodiversity and of ecological communities.
Mutationism is one of several alternatives to evolution by natural selection that have existed both before and after the publication of Charles Darwin's 1859 book On the Origin of Species. In the theory, mutation was the source of novelty, creating new forms and new species, potentially instantaneously, in sudden jumps. This was envisaged as driving evolution, which was thought to be limited by the supply of mutations.
Intragenomic conflict refers to the evolutionary phenomenon where genes have phenotypic effects that promote their own transmission in detriment of the transmission of other genes that reside in the same genome. The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects cause their transmission to new organisms, and most genes achieve this by cooperating with other genes in the same genome to build an organism capable of reproducing and/or helping kin to reproduce. The assumption of the prevalence of intragenomic cooperation underlies the organism-centered concept of inclusive fitness. However, conflict among genes in the same genome may arise both in events related to reproduction and altruism.
Brian Charlesworth is a British evolutionary biologist at the University of Edinburgh, and editor of Biology Letters. Since 1997, he has been Royal Society Research Professor at the Institute of Evolutionary Biology (IEB) in Edinburgh. He has been married since 1967 to the British evolutionary biologist Deborah Charlesworth.
Coalescent theory is a model of how alleles sampled from a population may have originated from a common ancestor. In the simplest case, coalescent theory assumes no recombination, no natural selection, and no gene flow or population structure, meaning that each variant is equally likely to have been passed from one generation to the next. The model looks backward in time, merging alleles into a single ancestral copy according to a random process in coalescence events. Under this model, the expected time between successive coalescence events increases almost exponentially back in time. Variance in the model comes from both the random passing of alleles from one generation to the next, and the random occurrence of mutations in these alleles.
In biology, saltation is a sudden and large mutational change from one generation to the next, potentially causing single-step speciation. This was historically offered as an alternative to Darwinism. Some forms of mutationism were effectively saltationist, implying large discontinuous jumps.
Alexey Simonovich Kondrashov worked on a variety of subjects in evolutionary genetics. He is best known for the deterministic mutation hypothesis explaining the maintenance of sexual reproduction, his work on sympatric speciation, and his work on evaluating mutation rates.
Experimental evolution studies are a means of testing evolutionary theory under carefully designed, reproducible experiments. Given enough time, space, and money, any organism could be used for experimental evolution studies. However, those with rapid generation times, high mutation rates, large population sizes, and small sizes increase the feasibility of experimental studies in a laboratory context. For these reasons, bacteriophages are especially favored by experimental evolutionary biologists. Bacteriophages, and microbial organisms, can be frozen in stasis, facilitating comparison of evolved strains to ancestors. Additionally, microbes are especially labile from a molecular biologic perspective. Many molecular tools have been developed to manipulate the genetic material of microbial organisms, and because of their small genome sizes, sequencing the full genomes of evolved strains is trivial. Therefore, comparisons can be made for the exact molecular changes in evolved strains during adaptation to novel conditions.
Günter P. Wagner is an Austrian-born evolutionary biologist who is Professor of Ecology and Evolutionary biology at Yale University, and head of the Wagner Lab.
Laurence Daniel Hurst is a Professor of Evolutionary Genetics in the Department of Biology and Biochemistry at the University of Bath and the director of the Milner Centre for Evolution.
The following outline is provided as an overview of and topical guide to evolution:
Epistasis is a phenomenon in genetics in which the effect of a gene mutation is dependent on the presence or absence of mutations in one or more other genes, respectively termed modifier genes. In other words, the effect of the mutation is dependent on the genetic background in which it appears. Epistatic mutations therefore have different effects on their own than when they occur together. Originally, the term epistasis specifically meant that the effect of a gene variant is masked by that of a different gene.
References
- 1 2 "Jon Seger's Research Interests". Archived from the original on 2010-06-09. Retrieved 2010-04-06.
- ↑ "If mutations occur at random over the entire sequence of a species' genome, how can a complex organ such as an eye evolve? How can all the mutations that direct the development of that organ be concentrated in the right places?". Scientific American .
- ↑ "Annual Report of the Smithsonian Institution 1970". archive.org. City of Washington: Smithsonian Institution Press. 30 June 1970. Retrieved 19 May 2017.
- ↑ "Jon Seger". MacArthur Foundation. 1 July 1987.
- ↑ "Fellows by Domain and Area (OLD) - MacArthur Foundation". Archived from the original on 2010-08-14. Retrieved 2010-04-06.
- ↑ "Issue Highlights". Genetics. 184 (2). February 2010.