- For a non-technical introduction to the topic, please see Introduction to evolution.
| Part of the Biology series on | | Evolution | | | | Mechanisms and processes | | Adaptation
Genetic drift
Gene flow
Mutation
Selection
Speciation Image File history File links Padlock. ...
Look up evolution in Wiktionary, the free dictionary. ...
Evolution is change in organisms over generations. ...
This article or section does not cite its references or sources. ...
Image File history File links Tree_of_life. ...
A biological adaptation is an anatomical structure, physiological process or behavioral trait of an organism that has evolved over a period of time by the process of natural selection such that it increases the expected long-term reproductive success of the organism. ...
In population genetics, genetic drift is the statistical effect that results from the influence that chance has on the success of alleles (variants of a gene). ...
Gene flow (also known as gene migration) is the transfer of genes from one population to another. ...
It has been suggested that mutant be merged into this article or section. ...
Selection is hierachically classified into natural and artificial selection. ...
Charles Darwins first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837) Speciation is the evolutionary process by which new biological species arise. ...
| | Research and history | | Evidence
History
Modern synthesis
Social effect / Objections While on board HMS Beagle, Charles Darwin collected numerous specimens, many new to science, which supported his later theory of evolution by natural selection. ...
The history of evolutionary thought is very long, since the idea of biological evolution has existed since ancient times, but the modern theory wasnt established until the 18th and 19th centuries, with scientists such as Jean-Baptiste Lamarck and Charles Darwin. ...
The modern evolutionary synthesis (often referred to simply as the new synthesis, the modern synthesis, the evolutionary synthesis, neo-Darwinian synthesis or neo-Darwinism), generally denotes the integration of Charles Darwins theory of the evolution of species by natural selection, Gregor Mendels theory of genetics as the basis...
The theory of transmutation had early origins in the speculations and hypotheses of Erasmus Darwin, and Jean-Baptiste Lamarck. ...
This ichthys fish parody reflects the view that Christianity and Darwinian evolution are in conflict, but that Christian TRUTH will triumph. ...
| | Evolutionary biology fields | | Ecological genetics
Evolutionary development
Human evolution
Molecular evolution
Phylogenetics
Population genetics
Evolutionary biology is a subfield of biology concerned with the origin and descent of species, as well as their change, multiplication, and diversity over time. ...
Ecological genetics is the study of genetics (itself a field of biology) from an ecological perspective. ...
Evolutionary developmental biology (evolution of development or informally, evo-devo) is a field of biology that compares the developmental processes of different animals in an attempt to determine the ancestral relationship between organisms and how developmental processes evolved. ...
This article does not cite its references or sources. ...
Molecular evolution is the process of the genetic material in populations of organisms changing over time. ...
In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ...
Population genetics is the study of the distribution of and change in allele frequencies under the influence of the four evolutionary forces: natural selection, genetic drift, mutation, and migration. ...
| | Biology Portal · v • d • e | In biology, evolution is the change in a population's inherited characteristics, or traits, from generation to generation. These traits are encoded as genes that are copied and passed on to offspring during reproduction. Random changes in these genes can produce new or altered traits, resulting in differences between organisms. Evolution occurs when these different traits become more common or rare in a population. This can occur randomly through genetic drift, or based on the reproductive value of traits through natural selection. This article or section does not cite its references or sources. ...
Heritability, as used professionally in genetics, has a very precise definition. ...
In biology, a trait or character is a genetically inherited feature of an organism. ...
For other meanings of this term, see gene (disambiguation). ...
Biological reproduction is the biological process by which new individual organisms are produced. ...
In population genetics, genetic drift is the statistical effect that results from the influence that chance has on the success of alleles (variants of a gene). ...
The Galápagos Islands hold 13 species of finches that are closely related and differ most markedly in the shape of their beaks. ...
Under natural selection, organisms with traits that help them to survive and reproduce tend to have more offspring. In doing so, they will pass more copies of inheritable beneficial traits on to the next generation. This leads to advantageous traits becoming more common in each generation, while disadvantageous traits become rarer.[1][2][3] Over time, this process can result in varied adaptations to changing environmental conditions.[4] As differences in and between populations accumulate, new species can evolve. All known species are descended from a single ancestor through this process of gradual divergence.[1][5][6] A biological adaptation is an anatomical structure, physiological process or behavioral trait of an organism that has evolved over a period of time by the process of natural selection such that it increases the expected long-term reproductive success of the organism. ...
Charles Darwins first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837) Speciation is the evolutionary process by which new biological species arise. ...
A group of organisms is said to have common descent if they have a common ancestor. ...
The theory of evolution by natural selection was first put forth in detail in Charles Darwin's 1859 book On the Origin of Species. In the 1930s, Darwinian natural selection was combined with Mendelian inheritance to form the modern evolutionary synthesis.[4] With its enormous explanatory and predictive power, this theory has become the central organizing principle of modern biology, providing a unifying explanation for the diversity of life on Earth.[7][8][9] Charles Robert Darwin (12 February 1809 – 19 April 1882) was an eminent English naturalist who achieved lasting fame by convincing the scientific community that species develop over time from a common origin. ...
British naturalist Charles Darwins book, The Origin of Species, is one of the pivotal works in scientific literature and arguably the pre-eminent work in biology. ...
Gregor Johann Mendel (July 20[1], 1822 – January 6, 1884) was an Augustinian abbot who is often called the father of modern genetics for his study of the inheritance of traits in pea plants. ...
Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their children; it underlies much of genetics. ...
The modern evolutionary synthesis (often referred to simply as the new synthesis, the modern synthesis, the evolutionary synthesis, neo-Darwinian synthesis or neo-Darwinism), generally denotes the integration of Charles Darwins theory of the evolution of species by natural selection, Gregor Mendels theory of genetics as the basis...
The New York Times reported on Einsteins confirmed prediction. ...
Rainforests are among the most biodiverse ecosystems on earth Biodiversity or biological diversity is the variation of taxonomic life forms within a given ecosystem, biome or for the entire Earth. ...
Basic processes Evolution consists of two basic types of processes: those that introduce new genetic variation into a population, and those that affect the frequencies of existing genes.[10] Random copying errors in genetic material (mutations), migration between populations (gene flow), and the reshuffling of genes during sexual reproduction (genetic recombination) create variation in organisms. In some organisms, like bacteria and plants, variation is also produced through horizontal gene transfer (the transfer of genetic material between organisms that are not directly related) and the mixing of genetic material by hybridization (interbreeding between species). Genetic variation is the variation in the genetic material of a population, and includes the nuclear, mitochodrial, ribosomal genomes as well as the genomes of other organelles. ...
Genetic material is used to store the genetic information of an organic life form. ...
It has been suggested that mutant be merged into this article or section. ...
Gene flow (also known as gene migration) is the transfer of genes from one population to another. ...
Sexual reproduction is a type of reproduction that results in increasing genetic diversity of the offspring. ...
It has been suggested that chromosomal crossover be merged into this article or section. ...
Horizontal gene transfer (HGT), also Lateral gene transfer (LGT), is any process in which an organism transfers genetic material to another cell that is not its offspring. ...
// In biology, hybrid has two meanings. ...
Genetic drift and natural selection act on this variation by increasing or decreasing the frequency of traits: genetic drift does so randomly, while natural selection does so based on whether a trait is beneficial, or conducive to reproduction. In population genetics, genetic drift is the statistical effect that results from the influence that chance has on the success of alleles (variants of a gene). ...
The Galápagos Islands hold 13 species of finches that are closely related and differ most markedly in the shape of their beaks. ...
Variation -
The variation in a population's apparent traits, or phenotypes, is primarily the result of the specific genetic makeup, or genotypes, encoded on DNA molecules called chromosomes. A specific location on a chromosome is known as a locus; a variant of a DNA sequence at a given locus is an allele. The modern evolutionary synthesis defines evolution as the change in the relative frequencies of alleles in a population. The variation between different DNA codings (alleles) at various loci is thus considered responsible for evolutionary change. Genetic variation is the variation in the genetic material of a population, and includes the nuclear, mitochodrial, ribosomal genomes as well as the genomes of other organelles. ...
Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. ...
The genotype is the specific genetic makeup (the specific genome) of an individual, in the form of DNA. Together with the environmental variation that influences the individual, it codes for the phenotype of that individual. ...
The structure of part of a DNA double helix Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the development and function of living organisms. ...
Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ...
Short and long arms Chromosome. ...
In genetics, an allele (pronounced al-eel or al-e-ul) is any one of a number of viable DNA codings occupying a given locus (position) on a chromosome. ...
The modern evolutionary synthesis (often referred to simply as the new synthesis, the modern synthesis, the evolutionary synthesis, neo-Darwinian synthesis or neo-Darwinism), generally denotes the integration of Charles Darwins theory of the evolution of species by natural selection, Gregor Mendels theory of genetics as the basis...
Allele frequency is a measure of the relative frequency of an allele on a genetic locus in a population. ...
Genetic variation is often the result of a new mutation in a single individual; in subsequent generations, the frequency of that variant may fluctuate in the population, becoming more or less prevalent relative to other alleles at the site. All evolutionary forces act by driving this change in allele frequency in one direction or another. Variation disappears when an allele reaches the point of fixation—when it either reaches a frequency of zero and disappears from the population, or reaches a frequency of one and replaces the ancestral allele entirely. In population genetics, fixation occurs when every individual within a population has the same allele at a particular locus. ...
Most sites in the complete DNA sequence, or genome, of a species are identical in all individuals in the population. Consequently, relatively small genotypic changes can lead to dramatic phenotypic ones. Sites with more than one allele are called polymorphic, or segregating, sites. Polymorphism leads to distinct groups of traits arising within the same species, such as different hair colors or sexes. Interactions between a genotype and the environment may also affect the phenotype, as reflected in developmental and phenotypic plasticity. In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ...
In biology, polymorphism (from Greek: poly many, morph form) can be defined as discontinuous genetic variation that results in the occurrence of several different forms or types of individuals among the members of a single species. ...
This article or section does not cite its references or sources. ...
This article or section does not cite its references or sources. ...
We dont have an article called Phenotypic plasticity Start this article Search for Phenotypic plasticity in. ...
Heredity -
Gregor Mendel's work provided the first firm basis to the idea that heredity occurred in discrete units. He noticed several traits in peas that occur in only one of two forms (e.g., the peas were either "round" or "wrinkled"), and was able to show that the traits were: heritable (passed from parent to offspring); discrete (i.e., if one parent had round peas and the other wrinkled, the progeny were not intermediate, but either round or wrinkled); and distributed to progeny in a well-defined and predictable manner (Mendelian inheritance). His research laid the foundation for the concept of discrete heritable traits, known today as genes. After Mendel's work was "rediscovered" in 1900, the concepts involved were found to have wide applicability, and it was found that most complex traits were polygenetic and not controlled by single-unit characters. Heredity (the adjective is hereditary) is the transfer of characteristics from parent to offspring, either through their genes or through the social institution called inheritance (for example, a title of nobility is passed from individual to individual according to relevant customs and/or laws). ...
Image File history File links ADN_static. ...
Image File history File links ADN_animation. ...
Gregor Johann Mendel (July 20[1], 1822 – January 6, 1884) was an Augustinian abbot who is often called the father of modern genetics for his study of the inheritance of traits in pea plants. ...
Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their children; it underlies much of genetics. ...
In biology, a trait or character is a genetically inherited feature of an organism. ...
For other meanings of this term, see gene (disambiguation). ...
Later research gave a physical basis to the notion of genes, and eventually identified DNA as the genetic material, with genes functioning as discrete elements within DNA. DNA is not perfectly copied, and rare mistakes (mutations) in genes can affect traits that the genes control (e.g., pea shape). The structure of part of a DNA double helix Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the development and function of living organisms. ...
A gene can have modifications such as DNA methylation, which do not change the nucleotide sequence of a gene, but do result in the epigenetic inheritance of a change in the expression of that gene in a trait. Another epigenetic mechanism is via microRNA and RNA interference, which serve regulatory roles in gene transcription and translation. DNA methylation is a type of chemical modification of DNA that can be inherited without changing the DNA sequence. ...
Epigenetics is the study of reversible heritable changes in gene function that occur without a change in the sequence of nuclear DNA. It is also the study of the processes involved in the unfolding development of an organism. ...
The stem-loop secondary structure of a pre-microRNA from Brassica oleracea. ...
Figure 1. ...
Non-DNA based forms of heritable variation exist, such as transmission of the secondary structures of prions or structural inheritance of patterns in the rows of cilia in protozoans such as Paramecium[12] and Tetrahymena.[13] Investigations continue into whether these mechanisms allow for the production of specific beneficial heritable variation in response to environmental signals. If this were shown to be the case, then some instances of evolution would lie outside of the typical Darwinian framework, which avoids any connection between environmental signals and the production of heritable variation. However, the processes that produce these variations are rather rare, often reversible, and leave the genetic information intact. A prion (IPA: [1] ) — short for proteinaceous infectious particle — (by analogy to virion) is a type of infectious agent. ...
Structural inheritance is the transmission of a trait in a living organism by a self-perpetuating spatial structures. ...
Mutation -
 Mutation can occur because of "copy errors" during DNA replication. Genetic variation arises due to random mutations that occur at a certain rate in the genomes of all organisms. Mutations are permanent, transmissible changes to the genetic material (usually DNA or RNA) of a cell, and can be caused by: "copying errors" in the genetic material during cell division; by exposure to radiation, chemicals, or viruses. In multicellular organisms, mutations can be subdivided into germline mutations that occur in the gametes and thus can be passed on to progeny, and somatic mutations that can lead to the malfunction or death of a cell and can cause cancer. It has been suggested that mutant be merged into this article or section. ...
DNA replication. ...
DNA replication. ...
The word random is used to express lack of purpose, cause, order, or predictability in non-scientific parlance. ...
In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ...
Genetic material is used to store the genetic information of an organic life form. ...
Ribonucleic acid (RNA) is a nucleic acid polymer consisting of nucleotide monomers. ...
Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell. Cells in culture, stained for keratin (red) and DNA (green). ...
This does not cite its references or sources. ...
Radioactive decay is the set of various processes by which unstable atomic nuclei emit subatomic particles (radiation). ...
Groups I: dsDNA viruses II: ssDNA viruses III: dsRNA viruses IV: (+)ssRNA viruses V: (-)ssRNA viruses VI: ssRNA-RT viruses VII: dsDNA-RT viruses A virus is a microscopic particle (ranging in size from 20 - 300 nm) that can infect the cells of a biological organism. ...
Gametes, from the ancient Greek γαμετης (spouse), are the specialized germ cells that come together during fertilization (conception) in organisms that reproduce sexually. ...
Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these cells to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ...
Mutations that are not affected by natural selection are called neutral mutations. Their frequency in the population is governed by mutation rate, genetic drift and selective pressure on linked alleles. It is understood that most of a species' genome, in the absence of selection, undergoes a steady accumulation of neutral mutations. In genetics, a neutral mutation is a mutation that occurs in an amino acid codon (presumably within an mRNA molecule) which results in the use of a different, but chemically similar, amino acid. ...
Individual genes can be affected by point mutations, also known as SNPs, in which a single base pair is altered. The substitution of a single base pair may or may not affect the function of the gene, while deletions and insertions of base pairs usually results in a non-functional gene.[14] A point mutation, or substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide. ...
A Single Nucleotide Polymorphism or SNP (pronounced snip) is a DNA sequence variation occurring when a single nucleotide - A, T, C, or G - in the genome (or other shared sequence) differs between members of a species (or between paired chromosomes in an individual). ...
Base pairs, of a DNA molecule. ...
Mobile elements, transposons, make up a major fraction of the genomes of plants and animals and appear to have played a significant role in the evolution of genomes. These mobile insertional elements can jump within a genome and alter existing genes and gene networks to produce evolutionary change and diversity.[15] Transposons are sequences of DNA that can move around to different positions within the genome of a single cell, a process called transposition. ...
On the other hand, gene duplications, which may occur via a number of mechanisms, are believed to be one major source of raw material for evolving new genes as tens to hundreds of genes are duplicated in animal genomes every million years.[16] Most genes belong to larger "families" of genes derived from a common ancestral gene (two genes from a species that are in the same family are dubbed "paralogs"). Another mechanism causing gene duplication is intergenic recombination, particularly "exon shuffling", i.e., an aberrant recombination that joins the "upstream" part of one gene with the "downstream" part of another.[17] Genome duplications and chromosome duplications also appear to have served a significant role in evolution. Genome duplication has been the driving force in the Teleostei genome evolution, where up to four genome duplications are thought to have happened, resulting in species with more than 250 chromosomes. Schematic of a region of a chromosome before and after a duplication event Gene duplication occurs when an error in homologous recombination, a retrotransposition event, or duplication of an entire chromosome leads to the duplication of a region of DNA containing a gene [1]. The significance of this process for...
In biology, two or more structures are said to be homologous if they are alike because of shared ancestry. ...
Polyploidy refers to cells or organisms that contain more than two copies of each of their chromosomes. ...
Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ...
Orders See text The Actinopterygii are the ray-finned fish. ...
Large chromosomal rearrangements do not necessarily change gene function, but do generally result in reproductive isolation, and, by definition, speciation; in sexual organisms, species are usually defined by the ability to interbreed). An example of this mechanism is the fusion of two chromosomes in the Homo genus that produced human chromosome 2; this fusion did not occur in the chimpanzee lineage, resulting in two separate chromosomes in extant chimpanzees. Charles Darwins first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837) Speciation is the evolutionary process by which new biological species arise. ...
Species Homo sapiens sapiens See text for extinct species. ...
Type species Simia troglodytes Blumenbach, 1775 distribution of Species Pan troglodytes Pan paniscus Chimpanzee, often shortened to chimp, is the common name for the two extant species in the genus Pan. ...
An evolutionary lineage (also called a clade) is composed of species, taxa, or individuals that are related by descent from a common ancestor. ...
Horizontal gene transfer Horizontal gene transfer (HGT) is any process in which an organism transfers genetic material to another organism that is not its offspring. This mechanism allows for the transfer of genetic material between unrelated organisms and is a form of gene flow. Image File history File links Phylogenetic_tree. ...
Image File history File links Phylogenetic_tree. ...
A phylogenetic tree, also called an evolutionary tree or a tree of life, is a tree showing the evolutionary interrelationships among various species or other entities that are believed to have a common ancestor. ...
A non-coding RNA (ncRNA) is any RNA molecule that is not translated into a protein. ...
For other meanings of this term, see gene (disambiguation). ...
The three-domain system is a biological classification introduced by Carl Woese in 1990 that emphasizes his separation of prokaryotes into two groups, originally called Eubacteria and Archaebacteria. ...
Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ...
Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota Halobacteria Methanobacteria Methanococci Methanopyri Archaeoglobi Thermoplasmata Thermococci Phylum Korarchaeota Phylum Nanoarchaeota Archaea (; from Greek αÏχαία, ancient ones; singular Archaeum, Archaean, or Archaeon), also called Archaebacteria (), is a major division of living organisms. ...
Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (IPA: ) is an organism with a complex cell or cells, in which the genetic material is organized into a membrane-bound nucleus or nuclei. ...
Carl Richard Woese (born July 15, 1928, Syracuse, New York) is an American microbiologist famous for defining the Archaea (a new domain or kingdom of life) in 1977 by phylogenetic taxonomy of 16S ribosomal RNA, a technique pioneered by Woese and which is now standard practice. ...
Horizontal gene transfer (HGT), also Lateral gene transfer (LGT), is any process in which an organism transfers genetic material to another cell that is not its offspring. ...
Many mechanisms for horizontal gene transfer have been observed, such as antigenic shift, reassortment, and hybridization. Viruses can transfer genes between species via transduction. Bacteria can incorporate genes from other dead bacteria or plasmids via transformation, exchange genes with living bacteria via conjugation, and have plasmids "set up residence separate from the host's genome".[18] Hybridization is highly significant in plant speciation,[19] and one out of ten species of birds are known to hybridize.[20] There are also examples of hybridization in mammals and insects;[21] however, this most often results in sterile offspring. Antigenic shift is the process by which two different strains of influenza combine to form a new subtype having a mixture of the surface antigens of the two original strains. ...
Reassortment is the exchange of DNA between viruses inside a host cell. ...
// In biology, hybrid has two meanings. ...
Transduction is the process by which bacterial DNA is moved from one bacterium to another by a virus. ...
Figure 1: Schematic drawing of a bacterium with plasmids enclosed. ...
Transformation is the genetic alteration of a cell resulting from the introduction, uptake and expression of foreign genetic material (DNA or RNA). ...
Bacterial conjugation is the transfer of genetic material between bacteria through cell-to-cell contact. ...
Horizontal gene transfer has been shown to result in the spread of antibiotic resistance across bacterial populations.[22] Furthermore, findings indicate that HGT has been a major mechanism for prokaryotic and eukaryotic evolution.[23][24] Antibiotic resistance is the ability of a micro-organism to withstand the effects of an antibiotic. ...
Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ...
Prokaryotes (pro-KAR-ee-oht) (from Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos, pl. ...
Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (IPA: ) is an organism with a complex cell or cells, in which the genetic material is organized into a membrane-bound nucleus or nuclei. ...
Horizontal gene transfer complicates the inference of the phylogeny of life, as the original metaphor of a tree of life no longer fits. Rather, since genetic information is passed to other organisms and other species in addition to being passed from parent to offspring, "biologists [should] use the metaphor of a mosaic to describe the different histories combined in individual genomes and use [the] metaphor of a net to visualize the rich exchange and cooperative effects of HGT among microbes".[25] In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ...
Mechanisms of evolution
Selection and adaptation -
Natural selection comes from differences in survival and reproduction. Differential mortality is the survival rate of individuals to their reproductive age. Differential fertility is the total genetic contribution to the next generation. Note that, whereas mutations and genetic drift are random, natural selection is not, as it preferentially selects for different mutations based on differential fitnesses. For example, rolling dice is random, but always picking the higher number on two rolled dice is not random. The central role of natural selection in evolutionary theory has given rise to a strong connection between that field and the study of ecology. The Galápagos Islands hold 13 species of finches that are closely related and differ most markedly in the shape of their beaks. ...
A biological adaptation is an anatomical structure, physiological process or behavioral trait of an organism that has evolved over a period of time by the process of natural selection such that it increases the expected long-term reproductive success of the organism. ...
Download high resolution version (800x638, 152 KB)Peacock displaying. ...
Download high resolution version (800x638, 152 KB)Peacock displaying. ...
Peacock re-directs here; for alternate uses see Peacock (disambiguation). ...
Illustration from The Descent of Man and Selection in Relation to Sex by Charles Darwin showing the Tufted Coquette Lophornis ornatus, female on left, ornamented male on right. ...
Random redirects here. ...
Ernst Haeckel coined the term oekologie in 1866. ...
Natural selection can be subdivided into two categories: ecological selection occurs when organisms that survive and reproduce increase the frequency of their genes in the gene pool over those that do not survive; and sexual selection occurs when organisms which are more attractive to the opposite sex because of their features reproduce more and thus increase the frequency of those features in the gene pool. Ecological selection (or environmental selection or survival selection or individual selection or asexual selection) refers to natural selection minus sexual selection, i. ...
Illustration from The Descent of Man and Selection in Relation to Sex by Charles Darwin showing the Tufted Coquette Lophornis ornatus, female on left, ornamented male on right. ...
Natural selection operates on mutations in a number of different ways. Arguably the most common form of selection is stabilizing selection, which decreases the frequency of harmful mutations; "living fossils" may be a result of this. Other forms of natural selection include directional selection, which increases the frequency of a beneficial mutation, and artificial selection, the purposeful breeding of a species. Stabilizing selection, also known as purifying selection or negative selection, is a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value. ...
Living fossil is a term for any living species (or clade) of organism which closely resembles species otherwise only known from fossils and has no close living relatives. ...
In population genetics, directional selection (sometimes referred to as positive selection) occurs when natural selection favors a single allele and therefore allele frequency continuously shifts in one direction. ...
This Chihuahua mix and Great Dane show the wide range of dog breed sizes created using artificial selection. ...
Through the process of natural selection, organisms become better adapted to their environments. Adaptation is any evolutionary process that increases the fitness of the individual, or sometimes the trait that confers increased fitness, e.g., a stronger prehensile tail or greater visual acuity. Note that adaptation is context-sensitive; a trait that increases fitness in one environment may decrease it in another. A biological adaptation is an anatomical structure, physiological process or behavioral trait of an organism that has evolved over a period of time by the process of natural selection such that it increases the expected long-term reproductive success of the organism. ...
Fitness (often denoted in population genetics models) is a central concept in evolutionary theory. ...
Most biologists believe that adaptation occurs through the accumulation of many mutations of small effect. However, macromutation is an alternative process for adaptation that involves a single, very large-scale mutation. Most biologists believe that adaptation occurs through the accumulation of small mutations. ...
Recombination -
In asexual organisms, variants in genes on the same chromosome will always be inherited together—they are linked, by virtue of being on the same DNA molecule. However, sexual organisms, in the production of gametes, shuffle linked alleles on homologous chromosomes inherited from the parents via meiotic recombination. This shuffling allows independent assortment of alleles (mutations) in genes to be propagated in the population independently. This allows bad mutations to be purged and beneficial mutations to be retained more efficiently than in asexual populations. It has been suggested that chromosomal crossover be merged into this article or section. ...
This article or section does not cite its references or sources. ...
Not to be confused with miosis. ...
Recombination usually refers to the biological process of genetic recombination and meiosis, a genetic event that occurs during the formation of sperm and egg cells. ...
Mendelian inheritance (or Mendelian genetics or Mendelism) is a set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their children; it underlies much of genetics. ...
However, the meitoic recombination rate is not very high - on the order of one crossover (recombination event between homologous chromosomes) per chromosome arm per generation. Therefore, linked alleles are not perfectly shuffled away from each other, but tend to be inherited together. This tendency may be measured by comparing the co-occurrence of two alleles, usually quantified as linkage disequilibrium (LD). A set of alleles that are often co-propagated is called a haplotype. Strong haplotype blocks can be a product of strong positive selection. Linkage disequilibrium (LD) is the non-random association of alleles at two or more loci on a chromosome. ...
A haplotype, a contraction of the phrase haploid genotype, is the genetic constitution of an individual chromosome. ...
Recombination is mildly mutagenic, which is one of the proposed reasons why it occurs with limited frequency. Recombination also breaks up gene combinations that have been successful in previous generations, and hence should be opposed by selection. However, recombination could be favoured by negative frequency-dependent selection (this is when rare variants increase in frequency) because it leads to more individuals with new and rare gene combinations being produced.
When alleles cannot be separated by recombination (for example in mammalian Y chromosomes), there is an observable reduction in effective population size, known as the Hill-Robertson effect, and the successive establishment of bad mutations, known as Muller's ratchet. The human Y chromosome is one of two sex chromosomes, it contains the genes that cause testis development, thus determining maleness. ...
The effective population size (Ne) is defined as the number of breeding individuals in an idealized population that would show the same amount of dispersion of allele frequencies under random genetic drift or the same amount of inbreeding as the population under consideration (Sewall Wright). ...
Hill and Robertson (1966) found an effect that explains why recombination is evolutionarily selected for. ...
In evolutionary genetics, Mullers ratchet is the name given to the process by which the genomes of an asexual population accumulate deleterious mutations in an irreversible manner (hence the word ratchet), a process which the genomes of sexual populations can easily reverse thanks to recombination. ...
Genetic drift -
Genetic drift is the change in allele frequency from one generation to the next as a result of the statistical effect of chance. The frequency of an allele in the offspring generation will vary according to a probability distribution of the frequency of the allele in the parent generation. Thus, over time even in the absence of selection upon the alleles, allele frequencies tend to "drift" upward or downward, eventually becoming "fixed" - that is, going to 0% or 100% frequency. Thus, fluctuations in allele frequency between successive generations may result in some alleles disappearing from the population due to chance alone. Two separate populations that begin with the same allele frequencies therefore might drift apart by random fluctuation into two divergent populations with different allele sets (for example, alleles present in one population could be absent in the other, or vice versa). In population genetics, genetic drift is the statistical effect that results from the influence that chance has on the success of alleles (variants of a gene). ...
Gene flow and population structure -
 Map of the world showing distribution of camelids. Solid black lines indicate possible migration routes. Gene flow, also called migration, is the exchange of genetic variation between populations, when geography and culture are not obstacles. Ernst Mayr thought that gene flow is likely to be homogenising, and therefore counteracting selective adaptation. Obstacles to gene flow result in reproductive isolation, a necessary condition for speciation. Gene flow (also known as gene migration) is the transfer of genes from one population to another. ...
Population genetics is the study of the distribution of and change in allele frequencies under the influence of the four evolutionary forces: natural selection, genetic drift, mutation, and migration. ...
Image File history File links Created by Jerry Crimson Mann 10:57, 2 August 2005 (UTC). ...
Image File history File links Created by Jerry Crimson Mann 10:57, 2 August 2005 (UTC). ...
Species Lama glama Lama guanicoe Vicugna pacos Vicugna vicugna Camelus dromedarius Camelus bactrianus The four llamas and two camels are camelids: members of the biological family Camelidae, the only family in the suborder Tylopoda. ...
Gene flow (also known as gene migration) is the transfer of genes from one population to another. ...
This article has been identified as possibly containing errors. ...
An important concept in evolutionary biology, reproductive isolation is a category of mechanisms that prevent two or more populations from exchanging genes. ...
Charles Darwins first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837) Speciation is the evolutionary process by which new biological species arise. ...
The free movement of alleles through a population may also be impeded by population structure, the size and geographical distribution of a population. For example, most real-world populations are not actually fully interbreeding; geographic proximity has a strong influence on the movement of alleles within the population. Population structure has profound effects on possible mechanisms of evolution.
The effect of genetic drift depends strongly on the size of the population: drift is important in small mating populations, where chance fluctuations from generation to generation can be large. The relative importance of natural selection and genetic drift in determining the fate of new mutations also depends on the population size and the strength of selection. Natural selection is predominant in large populations, while genetic drift is in small populations. Finally, the time for an allele to become fixed in the population by genetic drift (that is, for all individuals in the population to carry that allele) depends on population size—smaller populations require a shorter time for fixation.
An example of the effect of population structure is the founder effect, in which a population temporarily has very few individuals as a result of a migration or population bottleneck, and therefore loses much genetic variation. In this case, a single, rare allele may suddenly increase very rapidly in frequency within a specific population if it happened to be prevalent in a small number of "founder" individuals. The frequency of the allele in the resulting population can be much higher than otherwise expected, especially for deleterious, disease-causing alleles. Since population size has a profound effect on the relative strengths of genetic drift and natural selection, changes in population size can alter the dynamics of these processes considerably. Simple illustration of founder effect. ...
A population bottleneck (or genetic bottleneck) is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing, and the population is reduced by 50% or more, often by several orders of magnitude. ...
Speciation and extinction -
Speciation is the process by which new biological species arise. This may take place by various mechanisms. Allopatric speciation occurs in populations that become isolated geographically, such as by habitat fragmentation or migration.[26] Sympatric speciation occurs when new species emerge in the same geographic area.[27][28] Ernst Mayr's peripatric speciation is a type of speciation that exists in between the extremes of allopatry and sympatry. Peripatric speciation is a critical underpinning of the theory of punctuated equilibrium. An example of rapid sympatric speciation can be clearly observed in the triangle of U, where new species of Brassica sp. have been made by the fusing of separate genomes from related plants. Charles Darwins first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837) Speciation is the evolutionary process by which new biological species arise. ...
The Dodo, shown here in illustration, is an often-cited[1] example of modern extinction. ...
Image File history File links Download high resolution version (1024x768, 119 KB)Photo taken at Canterbury Museum in Christchurch, New Zealand File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...
Image File history File links Download high resolution version (1024x768, 119 KB)Photo taken at Canterbury Museum in Christchurch, New Zealand File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...
Species type (Marsh, 1878) Paul, 1987 Mateus , 2006 jimmadseni Chure, 2000 vide Glut, 2003 Synonyms Creosaurus Marsh, 1878 Labrosaurus Marsh, 1879 Camptonotus Marsh, 1879 ?Epanterias Cope, 1878 Allosaurus (IPA: ) was a large (up to 11. ...
Charles Darwins first sketch of an evolutionary tree from his First Notebook on Transmutation of Species (1837) Speciation is the evolutionary process by which new biological species arise. ...
Allopatric speciation, also known as geographic speciation, occurs when populations physically isolated by an extrinsic barrier evolve intrinsic (genetic) reproductive isolation such that if the barrier between the populations breaks down, individuals of the two populations can no longer interbreed. ...
Habitat fragmentation is a process of environmental change important in evolution and conservation biology. ...
Sympatry is one of three theoretical models for the phenomenon of speciation. ...
This article has been identified as possibly containing errors. ...
Peripatric speciation (also known as Parapatry) is a type of speciation in the theory of natural selection. ...
Punctuated equilibrium (or punctuated equilibria) is a theory in evolutionary biology which states that most sexually reproducing species will show little to no evolutionary change throughout their history. ...
The Triangle of U is a theory which describes the evolution and relationships between members of the plant genus Brassica. ...
One common misconception about evolution is the idea that if humans evolved from monkeys, monkeys should no longer exist. This misunderstands speciation, which frequently involves a subset of a population cladogenetically splitting off before speciating, rather than an entire species simply turning into a new one. Cladogenesis is particularly common when two subsets of a population are isolated from each other. Additionally, biologists have never claimed that humans evolved from monkeys—only that humans and monkeys share a common ancestor, as do all organisms.[29] Cladogenesis is an evolutionary splitting event in which each branch and its smaller branches is a clade; an evolutionary mechanism and a process of adaptive evolution that leads to the development of a greater variety of animals or plants. ...
Extinction is the disappearance of species (i.e., gene pools). The moment of extinction is generally defined as occurring at the death of the last individual of that species. Extinction is not an unusual event on a geological time scale—species regularly appear through speciation, and disappear through extinction. The Permian-Triassic extinction event was the Earth's most severe extinction event, rendering extinct 90% of all marine species and 70% of all terrestrial vertebrate species. In the Cretaceous-Tertiary extinction event, many forms of life perished (including approximately 50% of all genera), the most commonly mentioned among them being the non-avian dinosaurs. The Holocene extinction event is a current mass extinction, involving the rapid extinction of tens or hundreds of thousands of species each year. Scientists consider human activities to be the primary cause of the ongoing extinction event, as well as the related influence of climate change.[30] The Dodo, shown here in illustration, is an often-cited[1] example of modern extinction. ...
The gene pool of a species or a population is the complete set of unique alleles that would be found by inspecting the genetic material of every living member of that species or population. ...
The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. ...
The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. ...
An extinction event (also known as: mass extinction; extinction-level event, ELE) occurs when there is a sharp decrease in the number of species in a relatively short period of time. ...
Badlands near Drumheller, Alberta where erosion has exposed the KT boundary. ...
For other uses of the word, please see Genus (disambiguation). ...
Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Thyreophora Ornithopoda Marginocephalia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ...
The Dodo, a bird of Mauritius, became extinct during the mid-late 17th century after humans destroyed the forests where the birds made their homes and introduced animals that ate their eggs. ...
It has been suggested that Global warming in popular culture be merged into this article or section. ...
Cooperation Generally mathematical models incorporating mutation and natural selection have been used to model adaptation and evolution. Recent trends now incorporate "game theory" as more applicable to generating reliable models.[31] This work and others studies have focused attention on cooperation as a fundamental property needed for evolution to construct new levels of organization. Selfish replicators sacrificing their own reproductive potential to cooperate seems paradoxical in a competitive world. However a number of mechanisms have demonstrated the capacity to generate cooperation, and even altruism, such as kin selection, direct reciprocity, indirect reciprocity, network reciprocity, and group selection. The ubiquity of cooperation in the natural world and studies from the last twenty years reveal cooperation as a significant principle in constructive evolution.[32][33] Game theory is most often described as a branch of applied mathematics and economics that studies situations where players choose different actions in an attempt to maximize their returns. ...
Altruism is a well-documented animal behaviour, which appears most obviously in kin relationships but may also be evident amongst wider social groups. ...
Evidence of evolution -
 Tiktaalik in context: one of many species that track the evolutionary development of fish fins into tetrapod limbs. Evolution has left numerous signs of the histories of different species. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record. By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. While on board HMS Beagle, Charles Darwin collected numerous specimens, many new to science, which supported his later theory of evolution by natural selection. ...
Image File history File links Fishapods. ...
Image File history File links Fishapods. ...
Binomial name Tiktaalik roseae Daeschler, Shubin & Jenkins, 2006 Tiktaalik (IPA pronunciation: ) is a genus of extinct sarcopterygian (lobe-finned) fishes from the late Devonian period, with many features akin to those of tetrapods (four-legged animals). ...
Three small ammonite fossils, each approximately 1. ...
Comparative anatomy is the study of similarities and differences in the anatomy of organisms. ...
Anatomical drawing of the human muscles from the Encyclopédie. ...
The development of molecular genetics, and particularly of DNA sequencing, has allowed biologists to study the record of evolution left in organisms' genetic structures. The degrees of similarity and difference in the DNA sequences of modern species allows geneticists to reconstruct their lineages. It is from DNA sequence comparisons that figures such as the 96% genotypic similarity between humans and chimpanzees are obtained.[34][35] Molecular genetics is the field of biology which studies the structure and function of genes at a molecular level. ...
Other evidence used to demonstrate evolutionary lineages includes the geographical distribution of species. For instance, monotremes and most marsupials are found only in Australia, showing that their common ancestor with placental mammals lived before the submerging of the ancient land bridge between Australia and Asia. Families Kollikodontidae (extinct) Ornithorhynchidae - Platypus Tachyglossidae - Echidnas Steropodontidae (extinct) Monotremes are mammals that are best known for laying eggs, instead of giving birth to live young like marsupials and placental mammals (Eutheria). ...
Orders Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Marsupials are mammals in which the female typically has a pouch (called the marsupium, from which the name Marsupial derives) in which it rears its young through early infancy. ...
This article or section does not cite its references or sources. ...
Scientists correlate all of the above evidence, drawn from paleontology, anatomy, genetics, and geography, with other information about the history of Earth. For instance, paleoclimatology attests to periodic ice ages during which the world's climate was much cooler, and these are often found to match up with the spread of species which are better-equipped to deal with the cold, such as t
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