NationMaster - Encyclopedia: Mechanisms and processes of evolution

The mechanisms and processes of evolutionary change includes natural selection, genetic drift, gene flow, mutation, adaptation and speciation. Natural selection favors genes that improve capacity for survival and reproduction. Genetic drift is the random sampling of a generation's genes during reproduction, causing random changes in the frequency of alleles. Gene flow is the transfer of genes within and between populations. Mutations are changes in the DNA sequence of a cell's genome. Adaptations are structures or behaviors that enhance a specific function, causing organisms to become better at surviving and reproducing, and speciation is the process where a species diverges into two or more descendant species. For other uses, see Natural selection (disambiguation). ... 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). ... In population genetics, gene flow (also known as gene migration) is the transfer of alleles of genes from one population to another. ... It has been suggested that mutant be merged into this article or section. ... For other uses, see Adaptation (disambiguation). ... 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 relative importance of natural selection and genetic drift in a population varies depending on the strength of the selection and the effective population size, which is the number of individuals capable of breeding.^[1] Natural selection usually predominates in large populations, while genetic drift dominates in small populations. The dominance of genetic drift in small populations can even lead to the fixation of slightly deleterious mutations.^[2] As a result, changing population size can dramatically influence the course of evolution. Population bottlenecks, where the population shrinks temporarily and therefore loses genetic variation, result in a more uniform population.^[3] Bottlenecks also result from alterations in gene flow such as decreased migration, expansions into new habitats, or population subdivision.^[1] 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). ... 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. ... Simple illustration of founder effect. ...

Basic processes involved

Billions of years ago, as per the theory of evolution, chemicals randomly organized themselves into a self-replicating molecule. This spark of life was the seed of every living thing that used to exists or which exists today. That simplest life form, through the processes of mutation and natural selection, has been shaped into every living species on the planet. The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... In biology, offspring are the product of reproduction, a new organism produced by one or more parents. ... It has been suggested that mutant be merged into this article or section. ... For other uses, see Reproduction (disambiguation) Reproduction is the biological process by which new individual organisms are produced. ... For other uses, see Natural selection (disambiguation). ... 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. ... This article is about evolution in biology. ...

Natural selection

Natural selection is the process by which genetic mutations that enhance reproduction become, and remain, more common in successive generations of a population. It has often been called a "self-evident" mechanism because it necessarily follows from three simple facts: For other uses, see Natural selection (disambiguation). ... For other uses, see Natural selection (disambiguation). ... Fitness (often denoted in population genetics models) is a central concept in evolutionary theory. ... For other uses, see Natural selection (disambiguation). ...

These conditions produce competition between organisms for survival and reproduction. Consequently, organisms with traits that give them an advantage over their competitors pass these advantageous traits on, while traits that do not confer an advantage are not passed on to the next generation.

The central concept of natural selection is the evolutionary fitness of an organism. This measures the organism's genetic contribution to the next generation. However, this is not the same as the total number of offspring: instead fitness measures the proportion of subsequent generations that carry an organism's genes.^[5] Consequently, if an allele increases fitness more than the other alleles of that gene, then with each generation this allele will become more common within the population. These traits are said to be "selected for". Examples of traits that can increase fitness are enhanced survival, and increased fecundity. Conversely, the lower fitness caused by having a less beneficial or deleterious allele results in this allele becoming rarer — they are "selected against".^[6] Importantly, the fitness of an allele is not a fixed characteristic, if the environment changes, previously neutral or harmful traits may become beneficial and previously beneficial traits become harmful.^[7] Fitness (often denoted in population genetics models) is a central concept in evolutionary theory. ... Fecundity is the potential reproductive capacity of an organism or population, measured by the number of gametes (e. ...

Natural selection within a population for a trait that can vary across a range of values, such as height, can be categorized into three different types. The first is directional selection, which is a shift in the average value of a trait over time — for example organisms slowly getting taller.^[8] Secondly, disruptive selection is selection for extreme trait values and often results in two different values becoming most common, with selection against the average value. This would be when either short or tall organisms had an advantage, but not those of medium height. Finally, in stabilizing selection there is selection against extreme trait values on both ends, which causes a decrease in variance around the average value.^[9] This would, for example, cause organisms to slowly become all the same height. 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. ... Disruptive selection is a type of evolution that simultaneously favors individuals at both extremes of the distribution. ... In statistics, a bimodal distribution is a distribution with two different peaks — that is, there are two distinct values that measurements tend to center around. ... 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. ... In probability theory and statistics, the variance of a random variable (or somewhat more precisely, of a probability distribution) is a measure of its statistical dispersion, indicating how its possible values are spread around the expected value. ...

A special case of natural selection is sexual selection, which is selection for any trait that increases mating success by increasing the attractiveness of an organism to potential mates.^[10] Traits that evolved through sexual selection are particularly prominent in males of some animal species, despite traits such as cumbersome antlers, mating calls or bright colors that attract predators, decreasing the survival of individual males.^[11] This survival disadvantage is balanced by higher reproductive success in males that show these hard to fake, sexually selected traits.^[12] 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. ... The handicap principle is an idea proposed by the Israeli biologist Amotz Zahavi. ...

An active area of research is the unit of selection, with natural selection being proposed to work at the level of genes, cells, individual organisms, groups of organisms and even species.^[13]^[14] None of these models are mutually-exclusive and selection may act on multiple levels simultaneously.^[15] Below the level of the individual, genes called transposons try to copy themselves throughout the genome.^[16] Selection at a level above the individual, such as group selection, may allow the evolution of co-operation, as discussed below.^[17] This article does not cite any references or sources. ... 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 evolutionary biology, group selection refers to the idea that alleles can become fixed or spread in a population because of the benefits they bestow on groups, regardless of the fitness of individuals within that group. ...

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). ...

Sexual selection

In many species, males develop prominent secondary sexual characteristics. A few oft quoted examples are the peacock's tail, coloring and patterns in male birds (in general), voice calls in frogs and flashes in fireflies. Many of these traits are a liability from the standpoint of survival. Any pretentious trait or noisy, attention getting behavior will alert predators as well as potential mates. 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. ... This article is about the Male sex. ... This snapping turtle is trying to make a meal of a Canada goose, but the goose is too wary. ... Mate may refer to: Relationships: Mate (term), a term for a friend, especially in the United Kingdom and Australasia; also used to address strangers One of a pair of animals, sometimes also applied to a human partner; see mating Nautical: A deck officer on a merchant marine vessel, usually ranked...

Natural selection can be broken down into many components, of which survival is only one. Sexual attractiveness is a very major component of selection.

Sexual selection is natural selection operating on factors that contribute to an organism's mating success. Traits that are a liability to survival can evolve when the sexual attractiveness of a trait outweigh the liability incurred for survival. A male who lives a short time, but produces many progeny is much more successful than a long lived one that produces few. The former's genes will eventually dominate the gene pool of his species. In many species, especially polygynous species where only a few males monopolize all the females, sexual selection has caused distinct sexual dimorphism. In these species males compete against other males for mates. The competition can be either direct or mediated by female choice. In species where females choose, males compete by displaying striking phenotypic characteristics or by performing elaborate courtship behaviors. The females then mate with the males that most interest them, usually the ones with the most outlandish displays. There are many competing theories as to why females are attracted to these displays. Progeny can mean: A genetic descendant, see offspring. ... The term polygyny (Greek: poly many, gynaika woman) is used in related ways in social anthropology and sociobiology. ... A monopoly (from the Greek language monos, one + polein, to sell) is defined as a persistent market situation where there is only one provider of a product or service, in other words a firm that has no competitors in its industry. ... For other uses, see Female (disambiguation). ...

The good genes model states that the display indicates some component of male fitness. A good genes advocate would say that bright coloring in male birds indicates a lack of parasites. The females are cueing on some signal that is correlated with some other component of feasibility. Color is an important part of the visual arts. ... A parasite is an organism that spends a significant portion of its life in or on the living tissue of a host organism and which causes harm to the host without immediately killing it. ...

None of the above models are mutually exclusive. There are millions of sexually dimorphic species on this planet and the forms of sexual selection probably vary amongst them. This article is about the astronomical term. ...

Genetic drift

Genetic drift is the change in allele frequency from one generation to the next that occurs because alleles in the offspring generation are a random sample of those in the parent generation, and are thus subject to sampling error.^[3] As a result, when selective forces are absent or relatively weak, allele frequencies tend to "drift" upward or downward in a random walk. This drift halts when an allele eventually becomes fixed, either by disappearing from the population, or replacing the other alleles entirely. Genetic drift may therefore eliminate some alleles from a population due to chance alone, and two separate populations that began with the same genetic structure can drift apart by random fluctuation into two divergent populations with different sets of alleles.^[18] The time for an allele to become fixed by genetic drift depends on population size, with fixation occurring more rapidly in smaller populations.^[19] 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 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). ... Sampling is that part of statistical practice concerned with the selection of individual observations intended to yield some knowledge about a population of concern, especially for the purposes of statistical inference. ... In statistics, when analyzing collected data, the samples observed differ in such things as means and standard deviations from the population from which the sample is taken. ... Example of eight random walks in one dimension starting at 0. ... In population genetics, fixation occurs when every individual within a population has the same allele at a particular locus. ...

Although natural selection is responsible for adaptation, the relative importance of the two forces of natural selection and genetic drift in driving evolutionary change in general is an area of current research in evolutionary biology.^[20] These investigations were prompted by the neutral theory of molecular evolution, which proposed that most evolutionary changes are the result the fixation of neutral mutations that do not have any immediate effects on the fitness of an organism.^[21] Hence, in this model, most genetic changes in a population are the result of constant mutation pressure and genetic drift.^[22]
The neutral theory of molecular evolution (also, simply the neutral theory of evolution) is an influential theory that was introduced with provocative effect by Motoo Kimura in the late 1960s and early 1970s. ... 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. ...

Gene flow

Gene flow is the exchange of genes between populations, which are usually of the same species.^[23] Examples of gene flow within a species include the migration and then breeding of organisms, or the exchange of pollen. Gene transfer between species includes the formation of hybrid organisms and horizontal gene transfer. In population genetics, gene flow (also known as gene migration) is the transfer of alleles of genes from one population to another. ... // This article is about a biological term. ... 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. ... Image File history File links Download high-resolution version (1280x960, 307 KB) Photographers comment: [sic] some lionesses down below growling and pacing but they were in the shade so I didnt get very good pictures of them. ... Image File history File links Download high-resolution version (1280x960, 307 KB) Photographers comment: [sic] some lionesses down below growling and pacing but they were in the shade so I didnt get very good pictures of them. ... For other uses, see Lion (disambiguation). ... In population genetics, gene flow (also known as gene migration) is the transfer of alleles of genes from one population to another. ... In population genetics, gene flow (also known as gene migration) is the transfer of alleles of genes from one population to another. ... SEM image of pollen grains from a variety of common plants: sunflower (Helianthus annuus), morning glory (Ipomoea purpurea), prairie hollyhock (Sidalcea malviflora), oriental lily (Lilium auratum), evening primrose (Oenothera fruticosa), and castor bean (Ricinus communis). ... // This article is about a biological term. ... 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. ...

Migration into or out of a population can change allele frequencies. Immigration may add new genetic material to the established gene pool of a population. Conversely, emigration may remove genetic material. As barriers to reproduction between two diverging populations are required for the populations to become new species, gene flow may slow this process by spreading genetic differences between the populations. Gene flow is hindered by mountain ranges, oceans and deserts or even man-made structures such as the Great Wall of China, which has hindered the flow of plant genes.^[24] 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. ... 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. ... â€œGreat Wallâ€ redirects here. ...

Depending on how far two species have diverged since their last common ancestor, it may still be possible for them to produce offspring, as with horses and donkeys mating to produce mules.^[25] Such hybrids are generally infertile, due to the two different sets of chromosomes being unable to pair up during meiosis. In this case, closely-related species may regularly interbreed, but hybrids will be selected against and the species will remain distinct. However, viable hybrids are occasionally formed and these new species can either have properties intermediate between their parent species, or possess a totally new phenotype.^[26] The importance of hybridization in creating new species of animals is unclear, although cases have been seen in many types of animals,^[27] with the gray tree frog particularly well-studied.^[28] Dad does not seem too surprised; perhaps this has happened to him before! Last Common Ancestor (LCA) is the most recent common ancestor of two populations that came to be separated by a species barrier. ... Binomial name Equus caballus Linnaeus, 1758 The horse (Equus caballus, sometimes seen as a subspecies of the Wild Horse, Equus ferus caballus) is a large odd-toed ungulate mammal, one of ten modern species of the genus Equus. ... Binomial name Linnaeus, 1758 For other uses, see Donkey (disambiguation). ... For other uses, see Mule (disambiguation). ... // This article is about a biological term. ... Infertility primarily refers to the biological inability of a man or a woman to contribute to conception. ... For the figure of speech, see meiosis (figure of speech). ... Hybridization between two different species sometimes leads to a distinct phenotype. ... Binomial name LeConte, 1825 The Gray tree frog (Hyla versicolor) is a species of small arboreal frog native to much of the United States and into Canada. ...

Hybridization is, however, an important means of speciation in plants, since polyploidy (having more than two copies of each chromosome) is tolerated in plants more readily than in animals.^[29] Polyploidy is important in hybrids as it allows reproduction, with the two different sets of chromosomes each being able to pair with an identical partner during meiosis.^[30] Polyploids also have more genetic diversity, which allows them to avoid inbreeding depression in small populations.^[31] Polyploidy refers to cells or organisms that contain more than two copies of each of their chromosomes. ... It has been suggested that this article or section be merged into inbreeding. ...

Horizontal gene transfer is the transfer of genetic material from one organism to another organism that is not its offspring, this is most common among bacteria.^[32] In medicine, this contributes to the spread of antibiotic resistance, as when one bacteria acquires resistance genes it can rapidly transfer them to other species.^[33] Horizontal transfer of genes from bacteria to eukaryotes such as the yeast Saccharomyces cerevisiae and the adzuki bean beetle Callosobruchus chinensis may also have occurred.^[34]^[35] Viruses can also carry DNA between organisms, allowing transfer of genes even across biological domains.^[36] Gene transfer has also occurred within eukaryotic cells, from the chloroplast and mitochondrial genomes to nuclear genomes.^[37] 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. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Antibiotic resistance is the ability of a micro-organism to withstand the effects of an antibiotic. ... Binomial name Meyen ex E.C. Hansen Saccharomyces cerevisiae is a species of budding yeast. ... This article is about biological infectious particles. ... In biology, a domain (also superregnum, superkingdom, or empire) is the top-level grouping of organisms in scientific classification, higher than a kingdom. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... HeLa cells stained for DNA with the Blue Hoechst dye. ...

Mutation

Genetic variation comes from random mutations that occur in the genomes of organisms. Mutations are changes in the DNA sequence of a cell's genome and are caused by radiation, viruses, transposons and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication.^[38]^[39]^[40] These mutagens produce several different types of change in DNA sequences; these can either have no effect, alter the product of a gene, or prevent the gene from functioning. Studies in the fly Drosophila melanogaster suggest that about 70 percent of mutations are deleterious, and the remainder are either neutral or have a weak beneficial effect.^[41] Due to the damaging effects that mutations can have on cells, organisms have evolved mechanisms such as DNA repair to remove mutations.^[38] Therefore, the optimal mutation rate for a species is a trade-off between short-term costs, such as the risk of cancer, and the long-term benefits of advantageous mutations.^[42] It has been suggested that mutant be merged into this article or section. ... Molecular evolution is the process of the genetic material in populations of organisms changing over time. ... â€œRandomâ€ redirects here. ... Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. ... This article is about biological infectious particles. ... Transposons are sequences of DNA that can move around to different positions within the genome of a single cell, a process called transposition. ... In biology, a mutagen (Latin, literally origin of change) is a physical or chemical agent that changes the genetic information (usually DNA) of an organism and thus increases the number of mutations above the natural background level. ... For the figure of speech, see meiosis (figure of speech). ... DNA replication. ... A gene product is the biochemical material, either RNA or protein, resulting from expression of a gene. ... Binomial name Meigen, 1830[1] Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a two-winged insect that belongs to the Diptera, the order of the flies. ... DNA damage resulting in multiple broken chromosomes DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. ...

Large sections of DNA can also be duplicated, which is a major source of raw material for evolving new genes, with tens to hundreds of genes duplicated in animal genomes every million years.^[43] Most genes belong to larger families of genes of shared ancestry.^[44] Novel genes are produced either through duplication and mutation of an ancestral gene, or by recombining parts of different genes to form new combinations with new functions.^[45]^[46] For example, the human eye uses four genes to make structures that sense light: three for color vision and one for night vision; all four arose from a single ancestral gene.^[47] An advantage of duplicating a gene (or even an (entire genome) is that overlapping or redundant functions in multiple genes allows alleles to be retained that would otherwise be harmful, thus increasing genetic diversity.^[48] Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ... 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... A gene family is a set of genes defined by presumed homology, i. ... In biology, homology is any similarity between structures that is due to their shared ancestry. ... Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina of the eye which only function in relatively bright light. ... Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of photoreceptor, cone cells. ... Polyploid (in Greek: πολλαπλόν - multiple) cells or organisms contain more than one copy (ploidy) of their chromosomes. ... In engineering, the duplication of critical components of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe, is called redundancy. ...

Changes in chromosome number may also involve the breakage and rearrangement of DNA within chromosomes. For example, two chromosomes in the Homo genus fused to produce human chromosome 2; this fusion did not occur in the chimpanzee lineage and chimpanzees retain these separate chromosomes.^[49] In evolution, the most important role of such chromosomal rearrangements may be to accelerate the divergence of a population into new species by preserving genetic differences within populations.^[50] Species Homo sapiens See text for extinct species. ... An evolutionary lineage (also called a clade) is composed of species, taxa, or individuals that are related by descent from a common ancestor. ...

Sequences of DNA that can move about the genome, such as transposons, make up a major fraction of the genetic material of plants and animals, and may have been important in the evolution of genomes.^[51] For example, more than a million copies of the Alu sequence are present in the human genome, and these sequences have now been recruited to perform functions such as regulating gene expression.^[52] Another effect of these mobile DNA sequences is that when they move within a genome, they can mutate or delete existing genes and thereby produce genetic diversity.^[53] Transposons are sequences of DNA that can move around to different positions within the genome of a single cell, a process called transposition. ... An Alu sequence is a short stretch of DNA originally characterized by the action of the Alu restriction endonuclease. ... A graphical representation of the normal human karyotype. ... Gene expression, or simply expression, is the process by which the inheritable information which comprises a gene, such as the DNA sequence, is made manifest as a physical and biologically functional gene product, such as protein or RNA. Several steps in the gene expression process may be modulated, including the...

Adaptation

Adaptations are structures or behaviors that enhance a specific function, causing organisms to become better at surviving and reproducing.^[54] They are produced by a combination of the continuous production of small, random changes in traits, followed by natural selection of the variants best-suited for their environment.^[55] This process can cause either the gain of a new feature, or the loss of an ancestral feature. An example that shows both types of change is bacterial adaptation to antibiotic selection, with mutations causing antibiotic resistance by either modifying the target of the drug, or removing the transporters that allow the drug into the cell.^[56] However, many traits that appear to be simple adaptations are in fact exaptations: structures originally adapted for one function, but which coincidentally became somewhat useful for some other function in the process.^[57] One example is the African lizard Holapsis guentheri, which developed an extremely flat head for hiding in crevices, as can be seen by looking at its near relatives. However, in this species, the head has become so flattened that it assists in gliding from tree to tree - an exaptation.^[57] For other uses, see Adaptation (disambiguation). ... Staphylococcus aureus - Antibiotics test plate. ... Antibiotic resistance is the ability of a micro-organism to withstand the effects of an antibiotic. ... An exaptation is a biological adaptation where the biological function currently performed by the adaptation was not the function performed while the adaptation evolved under earlier pressures of natural selection. ...

As adaptation occurs through the gradual modification of existing structures, structures with similar internal organization may have very different functions in related organisms. This is the result of a single ancestral structure being adapted to function in different ways. The bones within bat wings, for example, are structurally similar to both human hands and seal flippers, due to the common descent of these structures from an ancestor that also had five digits at the end of each forelimb. Other idiosyncratic anatomical features, such as bones in the wrist of the panda being formed into a false "thumb," indicate that an organism's evolutionary lineage can limit what adaptations are possible.^[59] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Diversity Around 15 species; see list of cetaceans or below. ... A flipper is a digitless, typically flat limb evolved for movement through water. ... For other uses, see Adaptation (disambiguation). ... Diagram of an insect leg A leg is the part of an animals body that supports the rest of the animal above the ground and is used for locomotion. ... The human vermiform appendix is a vestigial structure; it no longer retains its original function. ... In biology, homology is any similarity between structures that is due to their shared ancestry. ... In anatomy, a sesamoid bone is a bone embedded within a tendon. ... Panda may refer to: // Giant Panda Panda (plant), a genus of the family Euphorbiaceae PANDAS or P.A.N.D.A.S. is Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptoccal infections Qinling Panda, a subspecies of the Giant Panda. ...

During adaption, some structures may lose their original function and become vestigial structures.^[60] Such structures may have little or no function in a current species, yet have a clear function in ancestral species, or other closely-related species. Examples include the non-functional remains of eyes in blind cave-dwelling fish,^[61] wings in flightless birds,^[62] and the presence of hip bones in whales and snakes.^[63] Examples of vestigial structures in humans include wisdom teeth,^[64] the coccyx,^[60] and the vermiform appendix.^[60] The human vermiform appendix is a vestigial structure; it no longer retains its original function. ... Wisdom teeth are third molars that usually appear between the ages of 16 and 24 (although they may appear when older, younger, or may not appear at all). ... The coccyx is formed of up to five vertebrae. ... In human anatomy, the vermiform appendix (or appendix, pl. ...

An area of current investigation in evolutionary developmental biology is the developmental basis of adaptations and exaptations.^[65] This research addresses the origin and evolution of embryonic development and how modifications of development and developmental processes produce novel features.^[66] These studies have shown that evolution can alter development to create new structures, such as embryonic bone structures that develop into the jaw in other animals instead forming part of the middle ear in mammals.^[67] It is also possible for structures that have been lost in evolution to reappear due to changes in developmental genes, such as a mutation in chickens causing embryos to grow teeth similar to those of crocodiles.^[68] 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. ... Views of a Foetus in the Womb, Leonardo da Vinci, ca. ... Embryogenesis is the process by which the embryo is formed and develops. ... This article or section does not adequately cite its references or sources. ... Genera Mecistops Crocodylus Osteolaemus See full taxonomy. ...

Speciation

Speciation is the process where a species diverges into two or more descendant species.^[69] It has been observed multiple times under both controlled laboratory conditions and in nature.^[70] In sexually-reproducing organisms, speciation results from reproductive isolation followed by genealogical divergence. There are four mechanisms for speciation. The most common in animals is allopatric speciation, which occurs in populations initially isolated geographically, such as by habitat fragmentation or migration. As selection and drift act independently in isolated populations, separation will eventually produce organisms that cannot interbreed.^[71] 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. ... 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. ... 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. ...

The second mechanism of speciation is peripatric speciation, which occurs when small populations of organisms become isolated in a new environment. This differs from allopatric speciation in that the isolated populations are numerically much smaller than the parental population. Here, the founder effect causes rapid speciation through both rapid genetic drift and selection on a small gene pool.^[72] Peripatric speciation (also known as Parapatry) is a type of speciation in the theory of natural selection. ... Simple illustration of founder effect. ...

The third mechanism of speciation is parapatric speciation. This is similar to peripatric speciation in that a small population enters a new habitat, but differs in that there is no physical separation between these two populations. Instead, speciation results from the evolution of mechanisms that reduce gene flow between the two populations.^[69] Generally this occurs when there has been a drastic change in the environment within the parental species' habitat. One example is the grass Anthoxanthum odoratum, which can undergo parapatric speciation in response to localized metal pollution from mines.^[73] Here, plants evolve that have resistance to high levels of metals in the soil. Selection against interbreeding with the metal-sensitive parental population produces a change in flowering time of the metal-resistant plants, causing reproductive isolation. Selection against hybrids between the two populations may cause reinforcement, which is the evolution of traits that promote mating within a species, as well as character displacement, which is when two species become more distinct in appearance.^[74] Parapatric speciation is a form of speciation in which the evolution of reproductive isolating mechanisms occurs when a population enters a new niche or habitat within the range of the parent species. ... Character displacement refers to the phenomenon where differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur but are minimized or lost where the speciesâ€™ distributions do not overlap. ...

Finally, in sympatric speciation species diverge without geographic isolation or changes in habitat. This form is rare since even a small amount of gene flow may remove genetic differences between parts of a population.^[75] Generally, sympatric speciation in animals requires the evolution of both genetic differences and non-random mating, to allow reproductive isolation to evolve.^[76] Image File history File linksMetadata No higher resolution available. ... Geographic isolation, or allopatry, is a term used in the study of evolution. ... Genera Geospiza Camarhynchus Certhidea Pinaroloxias Darwins finches (also known as the GalÃ¡pagos Finches) are 13 or 14 different but closely related species of finches Charles Darwin collected on the GalÃ¡pagos Islands during the voyage of the Beagle. ... This article is about the islands. ... Comparison of allopatric, peripatric, parapatric and sympatric speciation. ... In population genetics, gene flow (also known as gene migration) is the transfer of alleles of genes from one population to another. ... In biology, polymorphism can be defined as the occurrence in the same habitat of two or more forms of a trait in such frequencies that the rarer cannot be maintained by recurrent mutation alone. ... Assortative mating (also called Assortative pairing) takes place when sexually reproducing organisms tend to mate with individuals that are like themselves in some respect (positive assortative mating) or dissimilar (negative assortative mating). ...

One type of sympatric speciation involves cross-breeding of two related species to produce a new hybrid species. This is not common in animals as animal hybrids are usually sterile, because during meiosis the homologous chromosomes from each parent, being from different species cannot successfully pair. It is more common in plants, however because plants often double their number of chromosomes, to form polyploids. This allows the chromosomes from each parental species to form a matching pair during meiosis, as each parent's chromosomes is represented by a pair already.^[77] // This article is about a biological term. ... For the figure of speech, see meiosis (figure of speech). ... Homologous chromosomes are chromosomes in a biological cell that pair (synapse) during meiosis, or alternatively, non-identical chromosomes that contain information for the same biological features and contain the same genes at the same loci but possibly different genetic information, called alleles, at those genes. ... Polyploidy refers to cells or organisms that contain more than two copies of each of their chromosomes. ...

Indeed, chromosome doubling can itself cause reproductive isolation, as half the doubled chromosomes will be unmatched when breeding with undoubled organisms.^[78]

Speciation events are important in the theory of punctuated equilibrium, which accounts for the pattern in the fossil record of short "bursts" of evolution interspersed with relatively long periods of stasis, where species remain relatively unchanged.^[79] In this theory, speciation and rapid evolution are linked, with natural selection and genetic drift acting most strongly on organisms undergoing speciation in novel habitats or small populations. As a result, the periods of stasis in the fossil record correspond to the parental population, and the organisms undergoing speciation and rapid evolution are found in small populations or geographically-restricted habitats, and therefore rarely being preserved as fossils.^[80] 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. ...

Co-evolution

Co-evolution is the mutual evolutionary influence between two species. Each party in a co-evolutionary relationship exerts selective pressures on the other, thereby affecting each others' evolution.^[81] Co-evolution includes the evolution of a host species and its parasites, and examples of mutualism evolving through time. Evolution in response to abiotic factors, such as climate change, is not coevolution (since climate is not alive and does not undergo biological evolution). Evolution in a one-on-one interaction, such as that between predator and prey, host-symbiont or host-parasite pair, is coevolution. But many cases are less clearcut: a species may evolve in response to a number of other species, each of which is also evolving in response to a set of species. This situation has been referred to as "diffuse coevolution". And, certainly, for many organisms, the biotic (living) environment is the most prominent selective pressure, resulting in evolutionary change.^[81] Bumblebees and the flowers they pollinate have co-evolved so that both have become dependent on each other for survival. ... Bumblebee on Joe Pye Image copyleft: Image taken by me, released under GFDL Pollinator 03:31, Nov 9, 2004 (UTC) ( ) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Bumblebee on Joe Pye Image copyleft: Image taken by me, released under GFDL Pollinator 03:31, Nov 9, 2004 (UTC) ( ) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Species more than 250 species and subspecies in 38 subgenera Bumblebees (also spelled bumble bee, also known as humblebee) are flying insects of the genus Bombus in the family Apidae. ... For other uses, see Flower (disambiguation). ... Pollination is an important step in the reproduction of seed plants: the transfer of pollen grains (male gametes) to the plant carpel, the structure that contains the ovule (female gamete). ... Biological interactions result from the fact that organisms in an ecosystem interact with each other, in the natural world, no organism is an autonomous entity isolated from its surroundings. ... This article is about evolution in biology. ... For other uses, see Species (disambiguation). ... For other uses, see Selection (disambiguation). ... A parasite is an organism that spends a significant portion of its life in or on the living tissue of a host organism and which causes harm to the host without immediately killing it. ... In biology, mutualism is an interaction between two or more species, where both species derive benefit. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 450,000 years For current global climate change, see Global warming. ... Predator and Prey redirect here. ...

Co-evolution also occurs between predator and prey species as in the case of the Rough-skinned Newt (Taricha granulosa) and the common garter snake (Thamnophis sirtalis). In this case, the newts produce a potent nerve toxin that concentrates in their skin. Garter snakes have evolved resistance to this toxin through a set of genetic mutations, and prey upon the newts. The relationship between these animals has resulted in an evolutionary arms race that has driven toxin levels in the newt to extreme levels. (see Red Queen).^[81] This snapping turtle is trying to make a meal of a Canada goose, but the goose is too wary. ... Prey can refer to: Look up Prey in Wiktionary, the free dictionary A prey animal eaten by a predator in an act called predation. ... Binomial name Taricha granulosa // Subspecies Species Granulosa is divided into two subspecies: Rough-Skinned newt (Taricha granulosa granulosa) Crater Lake Rough-Skinned newt (Taricha granulosa mazamae) A newt with pebbly, non-slimy skin, that is light brown to black on top and yellow to orange on its belly, is most... Species See Taxonomy section. ... For other uses, see Toxin (disambiguation). ... It has been suggested that mutant be merged into this article or section. ... An evolutionary arms race is an evolutionary struggle between a predator species and its prey (including parasitism) that is said to resemble an arms race. ... This article is about the evolutionary hypothesis. ...

Co-evolutionary algorithms are also a class of algorithms used for generating artificial life as well as for optimization, game learning and machine learning.^[81] Pioneering results in the use of co-evolutionary methods were by Daniel Hillis (who co-evolved sorting networks) and Karl Sims (who co-evolved virtual creatures). Artificial Life, (commonly Alife or alife) is a field of study and art form that examines systems related to life, its processes and its evolution through simulations using computer models, robotics, and biochemistry [1] (called soft, hard, and wet approaches respectively[2]). Artificial life complements traditional Biology by trying to... As a broad subfield of artificial intelligence, machine learning is concerned with the design and development of algorithms and techniques that allow computers to learn. At a general level, there are two types of learning: inductive, and deductive. ... This article needs cleanup. ... Karl Sims is a researcher formerly with the MIT Media Lab who is most well known for using genetic programming to evolve virtual creatures that competed in various simulated environments as described in this paper. ...

See also

While on board HMS Beagle, Charles Darwin collected numerous specimens, many new to science, which supported his later theory of evolution by natural selection. ... For other uses, see Adaptation (disambiguation). ... Macroevolution refers to evolution that occurs at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population. ... Microevolution is the occurrence of small-scale changes in allele frequencies in a population, over a few generations, also known as change at or below the species level. ... 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. ... 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. ... For other uses, see Natural selection (disambiguation). ... 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). ... In population genetics, gene flow (also known as gene migration) is the transfer of alleles of genes from one population to another. ... It has been suggested that mutant be merged into this article or section. ... 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. ... We dont have an article called Phenotypic plasticity Start this article Search for Phenotypic plasticity in. ... Norms of reaction for two genotypes. ... Many organisms consist of modules, both anatomically and in their metabolism. ... Anagenesis is the progressive evolution of species involving a change in gene frequency in an entire population rather than a cladogenetic branching event. ... Catagenesis is an archaic term from evolutionary biology referring to evolutionary directions that were considered retrogressive. ... 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. ... Evolutionary thought has roots in antiquity as philosophical ideas conceived during the Ancient Greek and Roman eras, but until the 18th century, biological thought was dominated by essentialism, the idea that living forms are static and unchanging in time. ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ... Charles Darwins Origin of Species (publ. ... The modern evolutionary synthesis refers to a set of ideas from several biological specialities that were brought together to form a unified theory of evolution accepted by the great majority of working biologists. ... The evolutionary history of life and the origin of life are fields of ongoing geological and biological research. ... Ecological genetics is the study of genetics (itself a field of biology) from an ecological perspective. ... // For the history of humans on Earth, see History of the world. ... Molecular evolution is the process of the genetic material in populations of organisms changing over time. ... Phylogenetic groups, or taxa, can be monophyletic, paraphyletic, or polyphyletic. ... Biological systematics is the study of the diversity of life on the planet earth, both past and present, and the relationships among living things through time. ... This is a list of topics in evolutionary biology and evolution. ... This timeline of the evolution of life outlines the major events in the development of life on the planet Earth. ...

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Contents

Basic processes involved var ACE_AR = {Site: '756743', Size: '300250'};