To see a brief description of evolution in simpler language, visit the Simple Wikipedia article on evolution

Evolution is the ongoing process of change that has transformed life on earth from its simple beginnings into its present diversity.^[1] Evolution occurs through changes in genes, the "recipes" for constructing organisms. When an organism reproduces, small, random changes in its genes make the offspring different from the parents. Sometimes these changes increase the chances of an offspring surviving to reproduce. When this happens, the genes for the beneficial traits are passed on again, becoming more common in the next generation. Basic English is a simplified English language with a small number of words created by Charles Kay Ogden and described in his book Basic English: A General Introduction with Rules and Grammar (1930). ... Simple English Wikipedias logo Simple English Wikipedia is an English edition of the Wikipedia encyclopedia, written in Basic English. ... This article is about evolution in biology. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ...

Genes that do not help organisms reproduce may become rarer or be eliminated from the population. This is called natural selection. Through natural selection, populations of organisms slowly change over time as they adapt to changes in their environments.^[2] Darwins illustrations of beak variation in the finches of the Galápagos Islands, which hold 13 closely related species that differ most markedly in the shape of their beaks. ...

The theory of evolution is the explanation for how evolution occurs. This states that all living things are descended from a single common ancestor, which lived at some point in the distant past. This idea is called common descent. Evolution is often said to be both theory and fact. ... A group of organisms is said to have common descent if they have a common ancestor. ...

Since the beginning of life, evolution has transformed the first species into a very large number of different species, as life has found a variety of ways to survive and flourish. This has produced the variety of organisms that exist today. The theory of evolution does not address how life originated (abiogenesis), only how life has changed since its inception. This article does not adequately cite its references or sources. ... This article focuses on the history of thought regarding abiogenesis (the spontaneous generation of life from non-living sources). ...

Evolutionary biology, the scientific study of evolution, has itself undergone changes over time. For example, Gregor Mendel contributed a clear understanding of the role of genetics in variation between organisms.^[3] The field of population genetics came from a merger between evolutionary biology and genetics and addresses how new species develop. This process is called speciation and involves new species developing from ancestral forms. This article or section does not cite any references or sources. ... “Mendel” redirects here. ... This article is about the general scientific term. ... 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. ... 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. ...

Evolution is a well-supported explanation for a given set of data, not a mere hypothesis.^[4] The theory of evolution is supported by an immense body of scientific evidence, just like the "theory of gravity". The fields of molecular biology, paleontology, and taxonomy all contribute evidence that illuminates the evolutionary process. There is no serious disagreement among biologists that evolution does occur, and more than 99.9% of all professional biological scientists support evolution.^[5] It is the foundation of the research conducted in all fields of biology. However, some debate remains about some of the details of how evolution occurs, and how important different mechanisms and processes are in producing evolution. While on board HMS Beagle, Charles Darwin collected numerous specimens, many new to science, which supported his later theory of evolution by natural selection. ... Gravity is a force of attraction that acts between bodies that have mass. ... Molecular biology is the study of biology at a molecular level. ... Paleontology, palaeontology or palæontology (from Greek: paleo, ancient; ontos, being; and λόγος, logos, knowledge) is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. ... Look up taxonomy in Wiktionary, the free dictionary. ...

Contents 1 Darwin's idea 2 Mendel’s contribution 3 Population genetics 3.1 Some definitions 3.2 Hardy-Weinberg equilibrium 3.2.1 An example 4 Evidence of evolution 4.1 The fossil record 4.2 Comparative anatomy 4.3 Artificial selection 4.4 Molecular biology 4.5 Co-evolution 5 Species 5.1 Inter-species barriers 5.1.1 Prezygotic barriers 5.1.2 Postzygotic barriers 6 Different perspectives on the mechanism of evolution 6.1 Rate of change 6.2 Unit of change 7 Summary 8 Further reading 9 External links 9.1 Evolution websites 9.2 Videos about evolution 9.3 Printable Introduction to evolution 9.4 Genetics 10 Notes

Haeckel's Paleontological Tree of Vertebrates (c. 1879). The evolutionary history of species has been described as a "tree", with many branches arising from a single trunk. Each branch indicates a species, and each fork in a branch represents the ancestor diverging in form, becoming multiple new forms of life. While Haeckel's tree is somewhat outdated, it illustrates clearly the principles that more complex modern reconstructions can obscure.

Image File history File links Size of this preview: 368 × 599 pixel Image in higher resolution (1475 × 2400 pixel, file size: 574 KB, MIME type: image/jpeg) stock #7465800 (purchased and donated by Kosi Gramatikoff User:Kosigrim) I, the creator of this work, hereby release it into the public domain. ... Image File history File links Size of this preview: 368 × 599 pixel Image in higher resolution (1475 × 2400 pixel, file size: 574 KB, MIME type: image/jpeg) stock #7465800 (purchased and donated by Kosi Gramatikoff User:Kosigrim) I, the creator of this work, hereby release it into the public domain. ... Ernst Haeckel. ... Fig. ...

Darwin's idea

Charles Darwin proposed the theory of evolution by natural selection.

Gregor Mendel's work on the inheritance of traits laid the foundation for genetics.

Charles Darwin (1809-1882) proposed that there is unity in all life. Darwin viewed the history of life as a tree, each fork in the tree’s limbs representing shared ancestry. The tips of the limbs represent the modern species present today. This was especially controversial because humans did not receive a special place at the top of the evolutionary tree; they were merely one of many branches. To explain these relationships, he proposed that all living things are related and have descended from a common ancestor in a process he described as "descent with modification".^[6] The popular press of his day interpreted Darwin's views to imply that humans were descended from monkeys. In fact, however, evolution states that humans and present-day monkeys share a common ancestor. Image File history File links Download high resolution version (511x771, 34 KB) Summary Water-colour portrait of Charles Darwin painted by George Richmond in the late 1830s. ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ... Darwins illustrations of beak variation in the finches of the Galápagos Islands, which hold 13 closely related species that differ most markedly in the shape of their beaks. ... File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... “Mendel” redirects here. ... 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. ... This article is about the general scientific term. ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ... Darwins illustrations of beak variation in the finches of the Galápagos Islands, which hold 13 closely related species that differ most markedly in the shape of their beaks. ... A group of organisms is said to have common descent if they have a common ancestor. ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ...

Darwin's explanation of the mechanisms of evolution relies on his theory of natural selection, a theory he presented in the famous text The Origin of Species (published in 1859). The modern theory of natural selection incorporates five basic ideas: ^[2] Darwins illustrations of beak variation in the finches of the Galápagos Islands, which hold 13 closely related species that differ most markedly in the shape of their beaks. ... Charles Darwins Origin of Species (publ. ...

1. Organisms will produce more offspring than their habitat can sustain. There will be a "struggle to survive".^[7]
2. Not all the offspring will be identical.
3. Some of the differences between the offspring will be due to variations in their genetic makeup, the "code" that determines each organism's inherited traits.
4. Genetic variations that help an organism to survive and reproduce are more likely to be passed on to the next generation than genetic variations that are unhelpful.
5. Over time, helpful genetic variations will accumulate until a new species results. ^[8]

The end products of natural selection are organisms that are adapted to their present environments. Natural selection does not involve "progress" towards an ultimate goal; in fact, it is not goal-driven. Evolution does not necessarily make life forms more advanced, more intelligent, or more sophisticated. For example, fleas (wingless parasites) are descended from a winged, ancestral scorpionfly,^[9] and snakes are lizards that have lost the use for limbs. Organisms are merely the outcome of mutations that succeed or fail, dependent upon the environmental conditions at that time. In reality, when the environment changes, most species fail to adapt and become extinct. This reality is evident in the struggles species are currently facing as environments change because of global warming.^[10] Habitat (which is Latin for it inhabits) is the place where a particular species live and grow. ... This article is about the general scientific term. ... In genetics, heritability is the proportion of phenotypic variation in a population that is attributable to genetic variation among individuals. ... The hierarchy of scientific classification. ... Orthogenesis, orthogenetic evolution or autogenesis, is the hypothesis that life has an innate tendency to move in a unilinear fashion due to some internal or external driving force. The hypothesis is based on Essentialism, finalism and cosmic teleology and proposes an intrinsic drive which slowly transforms species. ... The evolution of complexity is an important outcome of the process of evolution. ... For other uses, see Flea (disambiguation). ... Families Nannochoristidae Boreidae (snow fleas) Siphonaptera (fleas) Meropeidae (earwig flies) Eomeropidae Apteropanorpidae Choristidae Panorpodidae Bittacidae (hanging flies) Panorpidae (scorpion flies) Mecoptera are an order of insects with about 600 species worldwide. ... Global mean surface temperatures 1850 to 2006 Mean surface temperature anomalies during the period 1995 to 2004 with respect to the average temperatures from 1940 to 1980 Global warming is the observed increase in the average temperature of the Earths atmosphere and oceans in recent decades and the projected...

Mendel’s contribution

Darwin’s theory of natural selection laid the groundwork for evolutionary theory, but he lacked an accurate explanation for the source of variations within the population. Like many of his predecessors, Darwin incorrectly deduced that heritable traits were a product of the environment. Such a view of evolution assumed that characteristics acquired during an organism's lifetime could be passed on to its offspring (e.g. giraffes stretching for leaves on higher branches would give birth to offspring with longer necks). This misconception (of the inheritance of acquired characters) became known as Lamarckism, after one of its primary supporters, Jean-Baptiste Lamarck (1744-1829). The suggestion that body structures used extensively to cope with the environment become better developed, while structures not used deteriorate, is not in fact supported by evidence.^[11] “Mendel” redirects here. ... This article is about the general scientific term. ... The inheritance of acquired characters (or characteristics) is the hereditary mechanism by which changes in physiology acquired over the life of an organism (such as muscle enlarged through use) are transmitted to offspring. ... Lamarckism or Lamarckian evolution is a theory put forward by the French biologist Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck, based on heritability of acquired characteristics, the once widely accepted idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring. ... Jean-Baptiste Lamarck. ...

The missing information necessary to help explain the emergence of new traits in the offspring was provided by developments in the field of genetics, pioneered by Gregor Mendel (1822-1884). Mendel’s experiments with breeding pea plants demonstrated that heredity in sexual reproduction works by reshuffling and recombining factors (genes) during sexual reproduction. Genes are the basic units of heredity in living organisms. A gene is a segment of a DNA molecule on a chromosome that directs the physical development and behavior of the organism.^[12] It is this reshuffling of the genetic code that ensures that no two individuals will be exact copies. The merging of Darwin's theory with an understanding of heredity led to the birth of the field of science called population genetics.^[13] This article is about the general scientific term. ... “Mendel” redirects here. ... 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. ...

Population genetics

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. ... Hardy–Weinberg principle for two alleles: the horizontal axis shows the two allele frequencies p and q, the vertical axis shows the genotype frequencies and the three possible genotypes are represented by the different glyphs In population genetics, the Hardy–Weinberg principle is a relationship between the frequencies of alleles...

Some definitions

White Peppered Moth

Black morph in Peppered moth evolution.

From a genetic viewpoint, evolution is a generation-to-generation change in the frequencies of alleles within a population that shares a common gene pool. An allele is one specific form of a gene; for example, a gene for coloration in moths may have two alleles, black and white. A population is a localized group of individuals belonging to the same species. For example, all the trout of the same species sharing a single stream is a population. A gene pool is the complete set of alleles in a single population. Each allele occurs a certain number of times in the gene pool. The fraction of genes that belong to a given allele is called the "allele frequency". Therefore, if half of the body-color genes are genes for black moths, then the black-body allele frequency is 0.50.^[14] Evolution consists of changes in the frequencies of alleles within a group of interbreeding organisms, as in Peppered moth evolution. Populations evolve, not individuals: evolution does not describe changes in individuals (such as how a child matures into an adult, or how a tree grows from a seed), but changes from one generation to another within a population.^[15] Image File history File linksMetadata Download high-resolution version (3000x2000, 1318 KB) Description: Biston betularia Source: picture taken by Olaf Leillinger at 2006-06-14 License: CC-BY-SA-2. ... Image File history File linksMetadata Download high-resolution version (3000x2000, 1318 KB) Description: Biston betularia Source: picture taken by Olaf Leillinger at 2006-06-14 License: CC-BY-SA-2. ... Binomial name Biston betularia Linnaeus, 1758 Subspecies The peppered moth (Biston betularia) is a temperate species of night-flying moth often used by educators as an example of natural selection. ... Image File history File linksMetadata Download high-resolution version (3000x2000, 1001 KB) Description: (Linnaeus, 1758) Source: picture taken by Olaf Leillinger at 2006-06-13 License: CC-BY-SA-2. ... Image File history File linksMetadata Download high-resolution version (3000x2000, 1001 KB) Description: (Linnaeus, 1758) Source: picture taken by Olaf Leillinger at 2006-06-13 License: CC-BY-SA-2. ... , the white-bodied peppered moth. ... Rainbow trout, Oncorhynchus mykiss Biwa trout (or Biwa salmon), Oncorhynchus masou rhodurus Trout is the common name given to a number of species of freshwater fish belonging to the salmon family, Salmonidae. ... 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. ... Allele frequency is a measure of the relative frequency of an allele on a genetic locus in a population. ... , the white-bodied peppered moth. ...

Hardy-Weinberg equilibrium

Gametes fuse during fertilization

A theory known as the "Hardy-Weinberg principle" states that the frequencies of alleles in a sufficiently large population will not change over time if the only forces acting on the population are: Image File history File links Sperm-egg. ... Image File history File links Sperm-egg. ... A gamete is a specialized germ cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. ... Categories: Biology stubs ... Hardy–Weinberg principle for two alleles: the horizontal axis shows the two allele frequencies p and q, the vertical axis shows the genotype frequencies and the three possible genotypes are represented by the different glyphs In population genetics, the Hardy–Weinberg principle (HWP) (also Hardy–Weinberg equilibrium (HWE), or Hardy...

1. random reshuffling of alleles during the formation of the gametes, such as the sperm and egg.
2. random combination of the genes in these sex cells during fertilization, the process in which the egg and sperm combine to form a new cell.^[16]
   

Gametes (in Greek: γαμέτες) —also known as sex cells, germ cells, or spores—are the specialized cells that come together during fertilization (conception) in organisms that reproduce sexually. ... Categories: Biology stubs ...

An example

White and black mice

Suppose a group of mice inhabit a barn. In this population, there are only two versions of the gene that controls fur color. One allele produces black fur and accounts for 75% of the genes, the other produces white fur and makes up the remaining 25% of the genes. If an allele’s chance of being passed on to the next generation is due entirely to random processes (the shuffling and combining that takes place in the formation of sex cells and fertilization), the allele frequencies will stay the same and the composition of the gene pool remains 75% black-coding genes and 25% white-coding genes. Since there is no change in the allelic frequencies, there is no evolutionary change in fur color. This population is in "Hardy-Weinberg equilibrium". Image File history File linksMetadata Download high resolution version (2516x1396, 648 KB) Summary Pet Mice Licensing I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ... Image File history File linksMetadata Download high resolution version (2516x1396, 648 KB) Summary Pet Mice Licensing I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ...

For this equilibrium to persist and no evolution to occur, the following conditions must be met:

1. The population must be large. Small populations can have chance fluctuations in the gene pool, a condition known as genetic drift.
2. There must be no exchange of members between populations. Such migration between populations is called gene flow.
3. The mutation rate must be insignificant. Mutations can create new alleles and thus change the frequency of the pre-existing alleles.
4. Mating must be random. There can be no preference for any particular allele during mate selection.
5. Natural selection must not occur. The chance that each allele has for survival and reproduction must be the same.

It is very rare, if not impossible, for all these conditions to be met in a natural population. Therefore, frequencies of alleles in a gene pool are always changing, resulting in evolution of populations over successive generations. 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. ... Sevenspotted Lady Beetles mating In biology, mating is the pairing of opposite-sex or hermaphroditic internal fertilization animals for copulation and, in social animals, also to raise their offspring. ... The word random is used to express lack of order, purpose, cause, or predictability in non-scientific parlance. ...

Evidence of evolution

During the voyage of the Beagle, naturalist Charles Darwin collected fossils in South America, and found fragments of armor like giant versions of the scales on the modern armadillos living nearby. On his return, the anatomist Richard Owen showed that the fragments were from gigantic extinct glyptodons, related to the armadillos. This was one of the patterns of distribution that helped Darwin to develop his theory.^[17]

Science has provided a wide range of evidence for evolution, with fossil records being most prominent. In addition, studies of the anatomical and genetic similarities between present-day species serve as additional evidence for evolution. Image File history File links Glyptodon-Armadillo. ... Image File history File links Glyptodon-Armadillo. ... On its second voyage, much of it chronicled by Charles Darwin in his book, The Voyage of the Beagle, the HMS Beagle crossed the Atlantic towards Tierra Del Fuego, and carried out surveying especially of the West coast of South America, as well as a number of Pacific islands. ... For other people of the same surname, and places and things named after Charles Darwin, see Darwin. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... Families Pampatheriidae (prehistoric) Glyptodontidae (prehistoric) Dasypodidae Armadillos are small placental mammals, known for having a bony armor shell. ... Sir Richard Owen KCB (July 20, 1804–December 18, 1892) was an English biologist, comparative anatomist and palaeontologist. ... This article or section is in need of attention from an expert on the subject. ... The inception of Darwins theory began with a search for explanations of contradictions in current Creationist ideas, and led him to formulate his theory of evolution which was eventually published in his book On the Origin of Species. ... Paleontology, palaeontology or palæontology (from Greek: paleo, ancient; ontos, being; and λόγος, logos, knowledge) is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. ... A fossil Ammonite Fossils are the mineralized remains of animals or plants or other traces such as footprints. ... Gradualism is the belief that changes occur, or ought to occur, slowly in the form of gradual steps (see also incrementalism) In politics, the concept of gradualism is used to describe the belief that change ought to be modified in small, discrete increments rather than abrubt changes such as revolutions... 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 Fossil (disambiguation). ...

French naturalist and zoologist Georges Cuvier studied fossils.

Archaeopteryx fossil.

From [1], in the public domain This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... Georges Cuvier Baron Georges Léopold Chrétien Frédéric Dagobert Cuvier (August 23, 1769–May 13, 1832) was a French naturalist and zoologist. ... A fossil Ammonite Fossils are the mineralized remains of animals or plants or other traces such as footprints. ... Image File history File links No higher resolution available. ...

The fossil record

Paleontology, the study of fossils, supports the idea that all living creatures are related. Fossils also provide evidence that accumulated changes over long periods led to the diverse forms of life we see today. The fossil itself reveals the organism's structure, and the age of the fossil reveals when the species existed. From this, relationships can be established between present and extinct species, allowing paleontologists to construct family trees that link all life forms.^[18] Paleontology, palaeontology or palæontology (from Greek: paleo, ancient; ontos, being; and λόγος, logos, knowledge) is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. ...

Modern paleontology began with the work of Georges Cuvier (1769-1832). Cuvier noted that, in sedimentary rock, each layer contained a specific group of fossils. The deeper (older) the layer, the simpler the life forms. He also noted that many forms of life from the past are no longer present today. Cuvier proposed the idea of catastrophism, which explained the fossil record in the light of the theological views of his time. He proposed that catastrophes had occurred in localized areas throughout the earth’s history. Such areas were then repopulated by species that migrated in from nearby locations.^[19] Georges Cuvier Baron Georges Léopold Chrétien Frédéric Dagobert Cuvier (August 23, 1769–May 13, 1832) was a French naturalist and zoologist. ... Two types of sedimentary rock: limey shale overlaid by limestone. ... Catastrophism is the theory that Earth has been affected by sudden, short-lived, violent events that were sometimes worldwide in scope. ...

Nowadays, many more fossils have been discovered and identified. These fossils serve as a chronological record, documenting the emergence of new, more complex species from simpler ancestral forms. The fossil record also provides examples of transitional species that provide evidence of ancestral links between species that exist today.^[20] One such transitional fossil is Archaeopteryx, an ancient creature that had the distinct characteristics of a reptile, yet clearly possessed the feathers of a bird. The implication from such a find is that modern reptiles and birds arose from a common ancestor.^[21][22]
A transitional fossil or transitional form is the fossilized remains of a life form that illustrates an evolutionary transition. ... Species A. lithographica Meyer, 1861 (type) Synonyms See below Archaeopteryx (from Ancient Greek archaios meaning ancient and pteryx meaning feather or wing; pronounced Ar-kay-op-ter-iks ) is the earliest and most primitive known bird to date. ...

Comparative anatomy

Taxonomy is the branch of biology that names and classifies all living things. The founder of the science of taxonomy was Carolus Linnaeus (1707-1778). Linnaeus placed organisms into categories based on similar physical features (sometimes called their "morphology"). He never suggested that organisms which fell into similar groups were related; rather he followed the conventions of his time, that all species were uniquely created and remained fixed and unchanging. In evolutionary biology, convergent evolution is the process whereby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. ... Divergent evolution occurs when two or more biological characteristics have a common evolutionary origin but have diverged over evolutionary time. ... Taxonomy, sometimes alpha taxonomy, is the science of finding, describing and naming organisms, thus giving rise to taxa. ... Carl Linnaeus, Latinized as Carolus Linnaeus, also known after his ennoblement as  , (May 23, 1707[1] – January 10, 1778), was a Swedish botanist, physician and zoologist[2] who laid the foundations for the modern scheme of nomenclature. ... The term morphology in biology refers to the outward appearance (shape, structure, colour, pattern) of an organism or taxon and its component parts. ...

Today, scientists still use morphological similarities to assist them in categorizing life forms. However, these groupings are based on ancestral relationships. For example, orangutans, gorillas, chimpanzees, and humans all belong to the same taxonomic grouping referred to as a family – in this case the family called "Hominidae". These animals are grouped together because of similarities in morphology that come from common ancestry. A similarity in anatomical features because of shared ancestry is called homology.^[23] Type species Simia pygmaeus Linnaeus, 1760 Orangutan distribution Species Pongo pygmaeus Pongo abelii The orangutans are two species of great apes known for their intelligence and their long arms and reddish-brown hair. ... Type species Troglodytes gorilla Savage, 1847 distribution of Gorilla Species Gorilla gorilla Gorilla beringei The gorilla, the largest of the living primates, is a ground-dwelling omnivore that inhabits the forests of Africa. ... 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. ... This article is about modern humans. ... Genera The hominids are the members of the biological family Hominidae (the great apes), which includes humans, chimpanzees, gorillas, and orangutans. ... In biology, homology is any similarity between structures that is due to their shared ancestry. ...

Homologous structures. Note how the same basic design appears repeatedly in different types of forelimbs of different species.

Strong evidence for evolution comes from analysis of "homologous" structures that no longer perform the same task. One example is the forelimbs of mammals. The forelimbs of a human, cat, whale, and bat all have strikingly similar bone structures. However, each of these four species' forelimbs performs a different task. Such a "design" makes little sense if they are unrelated and uniquely constructed for their particular tasks. The theory of evolution explains these homologous structures: all four animals shared a common ancestor, and each has undergone change over many generations. These changes in structure have produced forelimbs adapted for different tasks. This is what Darwin described as "descent with modification".^[24] Image File history File links Handskelett_MK1888. ... Image File history File links Download high-resolution version (646x837, 58 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Introduction to evolution Talk:Introduction to evolution ... Image File history File linksMetadata Download high-resolution version (1600x1200, 823 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Introduction to evolution Talk:Introduction to evolution Metadata This file contains additional information, probably added from the digital... Image File history File linksMetadata Download high-resolution version (2576x1442, 1157 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Bird flight Wikipedia:Featured picture candidates/Aquila spinogaster Wikipedia:Featured picture candidates/September-2006 Introduction to evolution Talk... Image File history File linksMetadata Download high-resolution version (1853x1729, 873 KB) Summary Photo taken by me in July, 2004. ...

In some cases, anatomical comparison of structures in the embryos of two or more species provides evidence for a shared ancestor that is not obvious in the adult forms. Such homologies might be lost or take on different functions as the embryo develops. For example, part of the basis of classifying the vertebrate group (which includes humans), is the presence of a tail and pharyngeal gill slits.^[25] Because of the morphological similarities present in embryos of different species during development, it would be easy to assume that organisms re-enact their evolutionary history as an embryo – for example, human embryos passing through an amphibian then a reptilian stage before completing their development as mammals. This misconception is known as “ontogeny recapitulates phylogeny”. Such a re-enactment of evolution during embryonic development is not supported by scientific evidence. ^[26] For other uses, see Embryo (disambiguation). ... This article does not cite any references or sources. ... A scorpion tail The tail is the section at the rear end of an animals body; in general, the term refers to a distinct, flexible appendage to the torso. ... Pharyngeal gill slits are characteristic of chordates. ... For other uses, see Amphibian (disambiguation). ... Orders  Crocodilia - Crocodilians scary crocodiles. ... Ontogeny recapitulates phylogeny, also called the biogenetic law or the theory of recapitulation, is a now discredited hypothesis in biology first espoused in 1866 by Ernst Haeckel. ...

Vestigial structures

Whale skeleton showing vestigial hind leg bones

Homology also includes a unique group of shared structures referred to as "vestigial structures". The term "vestigial" refers to anatomical parts that are of minimal, if any, value to the organism that possesses them. These apparently illogical structures are remnants of organs that played an important role in ancestral forms. For example, whales still possess small vestigial leg bones which appear to be remnants of the legs that their ancestors used to walk on land.^[27] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The human vermiform appendix is a vestigial structure; it no longer retains its original function. ... This article is about the animal. ...

Humans also have many vestigial structures, including the ear muscles, the wisdom teeth, the appendix, the tail bone, body hair (including goose bumps), and the semilunar fold in the corner of the eye. The intrinsic muscles are the: The Helicis major is a narrow vertical band situated upon the anterior margin of the helix. ... 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). ... In human anatomy, the vermiform appendix (or appendix, pl. ... The coccyx, commonly referred to as the tailbone, is the final segment of the human vertebral column, of three to five (usually four) fused vertebrae (the coccygeal vertebrae), below the sacrum. ... Hair is also a musical: see Hair (musical) and Hair (movie) Hair is the filamentous outgrowth of the epidermis found in mammals. ... Goose bumps on a human Goose bumps, also called goose pimples, goose flesh, chill bumps, chicken skin, or the medical term cutis anserina, are the bumps on a persons skin at the base of body hairs which involuntarily develop when a person is cold or experiences strong emotions such... The plica semilunaris is small fold of tissue on the inside corner of the eye. ... This article refers to the sight organ. ...

Convergent evolution

Whitetip shark (left) compared to the bottlenose dolphin

Anatomical comparisons can also be misleading. Organisms which share similar environments will often develop similar physical features. This is known as "convergent evolution". For example, both sharks and dolphins have similar body forms, yet are only distantly related – sharks are fish and dolphins mammals. Such similarities are a result of both populations being exposed to the same selective pressures. Within both groups, changes that aid swimming would be favored. Thus, over time, they develop similar morphology, even though they are not closely related.^[2]
Image:Oceanic Whitetip Shark. ... Download high resolution version (2587x1709, 1092 KB) Wikipedia does not have an article with this exact name. ... Binomial name (Poey, 1861) Range of oceanic whitetip shark Synonyms Squalus maou, Lesson 1822-1825 Squalus longimanus, Poey 1861 Pterolamiops longimanus Carcharhinus obtusus, Garman 1881 Carcharhinus insularum, Snyder 1904 Pterolamiops magnipinnis, Smith 1958 Pterolamiops budkeri, Fourmanoir 1961 The oceanic whitetip shark, Carcharhinus longimanus, is a large pelagic shark of tropical... Binomial name Montagu, 1821 Bottlenose Dolphin range (in blue) The Bottlenose Dolphin is the most common and well-known dolphin. ... In evolutionary biology, convergent evolution is the process whereby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. ... Orders Carcharhiniformes Heterodontiformes Hexanchiformes Lamniformes Orectolobiformes Pristiophoriformes Squaliformes Squatiniformes † Symmoriida Sharks (superorder Selachimorpha) are fish with a full cartilaginous skeleton [1] and a streamlined body. ... Genera See article below. ... For other uses, see Fish (disambiguation). ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the production of milk in female mammary glands and by the presence of: hair, three middle ear bones used in hearing, and a neocortex region in... This page is a candidate for speedy deletion. ...

Artificial selection

The results of artificial selection: Great Danes and Chihuahuas

Artificial selection is the controlled breeding of domestic plants and animals. In controlled breeding, humans determine which animals will reproduce, and to some degree, which alleles will be passed to future generations. The process of artificial selection has a significant impact on the evolution of domestic animals. For example, people have produced different types of dogs by controlled breeding. The differences between the Chihuahua and the Great Dane are the result of artificial selection. Despite the dramatic differences in physical appearance, they share a recent common ancestor.^[28] Image File history File linksMetadata Download high-resolution version (1946x1589, 927 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Chihuahua (dog) Great Dane Introduction to evolution Metadata This file contains additional information, probably added from the digital... Image File history File linksMetadata Download high-resolution version (1946x1589, 927 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Chihuahua (dog) Great Dane Introduction to evolution Metadata This file contains additional information, probably added from the digital... This Chihuahua mix and Great Dane show the wide range of dog breed sizes created using artificial selection. ... The Great Dane is a breed of dog known for its giant size and gentle personality. ... This article does not cite any references or sources. ... This Chihuahua mix and Great Dane show the wide range of dog breed sizes created using artificial selection. ... Trinomial name Canis lupus familiaris The dog (Canis lupus familiaris) is a domestic subspecies of the wolf, a mammal of the Canidae family of the order Carnivora. ... This article does not cite any references or sources. ... The Great Dane is a breed of dog known for its giant size and gentle personality. ...

Darwin drew much of his support for natural selection from observing the outcomes of artificial selection. Much of his book On the Origin of Species was based on his observations of the diversity in domestic pigeons arising from artificial selection. Darwin proposed that if dramatic changes in domestic plants and animals could be achieved by humans in short periods, then natural selection, given millions of years, could produce the differences between living things today. In fact, there is no real difference in the genetic processes underlying artificial and natural selection. As in natural selection, the variations are a result of random mutations; the only difference is that in artificial selection, humans select which organisms will be allowed to breed.^[2] The 1859 edition of On the Origin of Species First published in 1859, The Origin of Species (full title On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life) by British naturalist Charles Darwin is one of the pivotal...

Molecular biology

A section of DNA

Every living organism contains molecules of DNA, RNA, and protein. If two organisms are closely related, these molecules will be very similar. On the other hand, if the organisms are distant relations, these molecules will be more different. For example, siblings share the closest relationship possible, and thus have very similar DNA sequences. The field of molecular systematics focuses on working out evolutionary relationships by measuring similarities in these molecules. Such molecular comparisons have allowed biologists to build a "relationship tree" of the evolution of various organisms. Scientists have made great strides in analyzing these molecules, particularly the DNA that makes up organisms' genes. The exact form of these genes is called the genotype, which influences the morphology (or phenotype) of an organism; thus, analyzing genes provides a clear understanding of the relationships between species. ^[29] Image File history File links Download high resolution version (799x2000, 915 KB) Summary An overview of the structure of DNA. Created by Michael Ströck (mstroeck) on February 8, 2006. ... Image File history File links Download high resolution version (799x2000, 915 KB) Summary An overview of the structure of DNA. Created by Michael Ströck (mstroeck) on February 8, 2006. ... 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. ... It has been suggested that molecular phylogeny be merged into this article or section. ...

Comparing both DNA and proteins has been extremely useful when studying species that are so closely related that there are no obvious anatomical differences. The extent of their relationship can be determined from how similar these molecules are. 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. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...

Genetic comparisons also allow scientists to draw conclusions about organisms whose common ancestors lived such a long time ago that morphological similarities are not apparent. For example, comparison of the DNA in chimpanzees with that of gorillas and humans demonstrated that chimpanzees share more genetic similarities with humans than with gorillas. Some studies suggest as much as 96% similarity between the genes of humans and chimps.^[30] Therefore, this implies that these two species, humans and chimpanzees, share a closer evolutionary relationship as well. ^[31] 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. ... Type species Troglodytes gorilla Savage, 1847 distribution of Gorilla Species Gorilla gorilla Gorilla beringei The gorilla, the largest of the living primates, is a ground-dwelling omnivore that inhabits the forests of Africa. ... This article is about modern humans. ...

Co-evolution

Co-evolution is a process in which two or more species influence the evolution of each other. All organisms are influenced by life around them; however, to meet the definition of "co-evolution", there must be evidence that some genetically determined traits in each species result from the interaction between the two organisms. ^[2] Bumblebees and the flowers they pollinate have co-evolved so that both have become dependent on each other for survival. ...

An extensively documented example of co-evolution involves the relationship between an ant called Pseudomyrmex and the acacia, a plant that the ant uses for food and shelter. The relationship between the two is so intimate that it has led to the evolution of special structures and behaviors in both organisms. The ant defends the acacia against herbivores and removes parasitic fungi from its leaves. In return, the plant has evolved swollen thorns which the ants use as shelter, and special flower parts which the ants eat. ^[32] Such co-evolution does not imply that the ants and the tree somehow choose to behave in such an altruistic (selfless concern for the welfare of others) manner for each others' benefit. Rather, across a population small genetic changes in both ant and tree benefited each on its own accord. The benefit gave a slightly higher chance of the characteristic being passed on to the next generation, where it gave the new tree (and the new ant colony) a greater chance of survival. Over time, successive mutations created the relationship we observe today. For other uses, see Ant (disambiguation). ... Pseudomyrmex is a genus of insect in family Formicidae. ... Species About 1,300; see List of Acacia species Acacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Linnaeus in 1773. ... A deer and two fawns feeding on some foliage A herbivore is often defined as any organism that eats only plants[1]. By that definition, many fungi, some bacteria, many animals, about 1% of flowering plants and some protists can be considered herbivores. ... Subkingdom/Phyla Chytridiomycota Blastocladiomycota Neocallimastigomycota Glomeromycota Zygomycota Dikarya (inc. ... For the ethical doctrine, see Altruism (ethics). ...

Species

Ernst Mayr

Given the right circumstances, and enough time, evolution leads to the emergence of new species. Scientists have struggled to find a precise and all-inclusive definition of a species. The classic definition, used here, was developed by Ernst Mayr (1904-2005). Mayr defined a species as a population or group of populations whose members have the potential to interbreed naturally with one another to produce viable, fertile offspring. Also, the members of a species cannot produce viable fertile offspring with members of other species. ^[1] Picture of Ernst Mayr from Ernst Mayr library website-- http://library. ... Picture of Ernst Mayr from Ernst Mayr library website-- http://library. ... This article has been identified as possibly containing errors. ... The hierarchy of scientific classification. ... 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. ... Phylogenetic groups, or taxa, can be monophyletic, paraphyletic, or polyphyletic. ... The hierarchy of scientific classification. ... This article has been identified as possibly containing errors. ... Viability means in general capacity for survival and is more specifically used to mean a capacity for living, developing, or germinating under favorable conditions. ...

Speciation is the lineage-splitting event that results in two separate species forming from a single common ancestral population. The most widely accepted method of speciation is called "allopatric speciation". This requires the geographic separation of a population. Separation may be due to a variety of geological forces such as the emergence of mountain ranges or the formation of canyons. For speciation to occur, separation must be complete to the point that genetic exchange between the two populations is completely disrupted. In their separate environments, the genetically isolated groups follow their own unique evolutionary pathways. Each group will accumulate different mutations as well as be subjected to different selective pressures. The accumulated genetic changes may result in separated populations that can no longer interbreed if they are reunited. If interbreeding is no longer possible, then they would be considered different species.^[33] A common criticism from those who reject evolution as a viable theory is their claim that speciation has never been observed. Speciation has been observed in several groups of organisms, including bacteria, round worms, insects, and fish; as well as in several groups of plants. In addition, past speciation events are recorded in fossils.^[34] 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. ...

There are numerous species of cichlids which demonstrate dramatic variations in morphology

For example, scientists have documented the formation of five new species of cichlid fishes from common ancestry since they were isolated less than 4000 years ago from the parent stock, in Lake Nagubago. The basis for speciation in this case was morphology (physical appearance) and lack of natural interbreeding. These fish have complex mating rituals and different coloration, which with only slight modifications would change the mate selection process. The five forms that arose could not be convinced to interbreed. ^[35] Image File history File linksMetadata Size of this preview: 800 × 492 pixel Image in higher resolution (2000 × 1229 pixel, file size: 775 KB, MIME type: image/jpeg) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cichlid Flowerhorn Metadata... Image File history File linksMetadata Size of this preview: 800 × 492 pixel Image in higher resolution (2000 × 1229 pixel, file size: 775 KB, MIME type: image/jpeg) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Cichlid Flowerhorn Metadata... Genera Apistogramma - Dwarf Cichlids Astronotus (Oscars) Boulengerochromis Cichlasoma - American Ciclids Crenicichla Pterophyllum - Freshwater Angelfish Symphysodon - Discus Teleogramma Tilapia Cichlids are a family of perciform fishes. ...

Inter-species barriers

Reproductive barriers that prevent interbreeding can be classified as either prezygotic barriers or postzygotic barriers.^[2]

Prezygotic barriers

Different species of Firefly do not recognize each others' mating signals, and as a result do not generally interbreed.

Prezygotic barriers prevent mating between species or prevent the fertilization of the egg if the species attempt to mate. Some examples are: Image File history File links Lampyris noctiluca, female, own picture, June 2005, Germany, File links The following pages link to this file: Firefly Lampyris ... Image File history File links Lampyris noctiluca, female, own picture, June 2005, Germany, File links The following pages link to this file: Firefly Lampyris ... Genera Curtos Cyphonocerus Drilaster Ellychnia Hotaria Lampyris Lucidina Lucidota Luciola - Japanese fireflies Phausis Photinus - common eastern firefly Photuris Pristolycus Pyractomena Pyrocoelia Stenocladius many others Wikispecies has information related to: Lampyridae Lampyridae is a family in the beetle order Coleoptera, members of which are commonly called fireflies, lightning bugs, or glow...

• Temporal isolation - Occurs when species mate at different times. Populations of the western spotted skunk (Spilogale gracilis) overlap with the eastern spotted skunk (Spilogale putorius) yet remain separate species because the former mates in summer and the latter in late winter.^[2]

• Behavioral isolation - Signals that elicit a mating response may be sufficiently different to prevent a desire to interbreed. The rhythmic flashing in male fireflies is species-specific and thus serves as a prezygotic barrier. ^[36]

• Mechanical isolation - Anatomical differences in reproductive structures may prevent interbreeding. This is especially true in flowering plants that have evolved specific structures adapted to certain pollinators. Mechanical barriers often contribute to reproductive isolation of flowers that are pollinated by insects. This has been well documented in the orchid family.

• Gametic isolation - The gametes of the two species are chemically incompatible, thus preventing fertilization. Gamete recognition may be based on specific molecules on the surface of the egg that attach only to complementary molecules on the sperm. Such mechanisms are common in fish species. ^[2]

• Geographic/habitat isolation - Geographic: The two species are separated by large-scale physical barriers, such as a mountain or large body of water, and therefore cannot mate with each other. This is illustrated in two separate species of antelope squirrels, genus Ammospermophilus, which inhabit opposite sides of the Grand Canyon. Habitat: The two species prefer different habitats, even if they live in the same general area, and therefore do not encounter each other. For example, two different species of garter snakes in the genus Thamnophis occur in the same area but one prefers the water while the other prefers dry land. ^[2]

The Mule is a hybrid of a horse and a donkey, and is usually infertile

The Eastern Spotted Skunk is a small, relatively slender skunk with small white spot on its forehead and another in front of each ear, the latter often confluent with a dorsolateral white stripe. ... Genera Curtos Cyphonocerus Drilaster Ellychnia Hotaria Lampyris Lucidina Lucidota Luciola - Japanese fireflies Phausis Photinus - common eastern firefly Photuris Pristolycus Pyractomena Pyrocoelia Stenocladius many others Wikispecies has information related to: Lampyridae Lampyridae is a family in the beetle order Coleoptera, members of which are commonly called fireflies, lightning bugs, or glow... A pollinator is the agent that moves pollen from the male anthers of a flower to the female stigma of a flower to accomplish fertilization or syngamy of the female gamete in the ovule of the flower by the male gamete from the pollen grain. ... Orchid re-directs here; for alternate uses see Orchid (disambiguation) Genera Over 800 See List of Orchidaceae genera. ... This article is about the canyon in the southwestern United States. ... Species many — see text A garter snake, or garden snake, or gardner snake, is any species of North American snake within the genus Thamnophis. ... Image File history File linksMetadata Download high-resolution version (1932x2576, 2005 KB) A mule in rural NE Oklahoma Taken by Terrill White File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File linksMetadata Download high-resolution version (1932x2576, 2005 KB) A mule in rural NE Oklahoma Taken by Terrill White File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... A barren of mules. ... Fertility is the ability of people or animals to produce healthy offspring in abundance. ...

Postzygotic barriers

Postzygotic barriers occur after fertilization, usually resulting in the formation of a hybrid zygote^[37] that is neither viable ^[38] nor fertile. This is typically a result of incompatible chromosomes in the zygote. Some examples include: It has been suggested that Biparental zygote be merged into this article or section. ...

• Reduced hybrid viability - A barrier between species occurs after the formation of the zygote, resulting in incomplete development and death of the offspring.

• Reduced hybrid fertility - Even if two different