Evidence of common descent 2339577 222172308 2008-06-27T22:27:08Z Firsfron 158443 link to article instead of redirect using [[Project:AutoWikiBrowser|AWB]] {{evolution3}} [[Image:HMS Beagle by Conrad Martens.jpg|thumb|right|300px|While on board [[HMS Beagle|HMS ''Beagle'']], [[Charles Darwin]] collected numerous specimens, many new to science, which supported his later theory of evolution by [[natural selection]].]] The wide range of '''evidence of common descent''' of living things strongly indicates the occurrence of [[evolution]] and provides a wealth of information on the natural processes by which the variety of life on [[Earth]] developed, supporting the [[modern evolutionary synthesis]]. [[Fossil]]s are important for estimating when various lineages developed. As fossilization is an uncommon occurrence, usually requiring hard body parts and death near a site where [[sediment]]s are being deposited, the fossil record only provides sparse and intermittent information about the [[evolution]] of life. [[scientific evidence|Evidence]] of [[organism]]s prior to the development of hard body parts such as shells, bones and teeth is especially scarce, but exists in the form of ancient [[microfossil]]s, as well as impressions of various soft-bodied organisms. Comparison of the genetic sequence of organisms has revealed that organisms that are [[phylogenetics|phylogenetically]] close have a higher degree of sequence similarity than organisms that are phylogenetically distant. Further evidence for [[common descent]] comes from genetic detritus such as [[pseudogene]]s, regions of DNA that are [[Homology (biology)#Orthology|orthologous]] to a gene in a related organism, but are no longer active and appear to be undergoing a steady process of degeneration. Since [[metabolism|metabolic]] processes do not leave fossils, research into the evolution of the basic cellular processes is done largely by comparison of existing organisms. Many lineages diverged at different stages of development, so it is possible to determine when certain metabolic processes appeared by comparing the traits of the descendants of a common ancestor. ==Evidence from genetics== Although it has only recently become available, the best evidence for common descent comes from the study of gene sequences. [[Sequence alignment|Comparative sequence analysis]] examines the relationship between the DNA sequences of different species, producing several lines of evidence that confirm Darwin's original hypothesis of common descent. If the hypothesis of common descent is true, then species that share a common ancestor will have inherited that ancestor's DNA sequence. Notably they will have inherited mutations unique to that ancestor. More closely-related species will have a greater fraction of identical sequence and will have shared substitutions when compared to more distantly-related species. The simplest and most powerful evidence is provided by [[Computational phylogenetics|phylogenetic reconstruction]]. Such reconstructions, especially when done using slowly-evolving protein sequences, are often quite robust and can be used to reconstruct a great deal of the evolutionary history of modern organisms (and even in some instances such as the recovered gene sequences of [[mammoth]]s, [[Neanderthal]]s or ''[[Tyrannosaurus|T. rex]]'', the evolutionary history of extinct organisms). These reconstructed phylogenies recapitulate the relationships established through morphological and biochemical studies. The most detailed reconstructions have been performed on the basis of the mitochondrial genomes shared by all [[eukaryote|eukaryotic]] organisms, which are short and easy to sequence; the broadest reconstructions have been performed either using the sequences of a few very ancient proteins or by using [[ribosomal RNA]] sequence. This evidence does not support the rival hypothesis that genetic similarity of two species is the product of common functional or structural requirements, and not common descent (for example, if there is one best way to produce a hoof, all hoofed creatures will share a genetic basis even if they are not related). However, phylogenetic relationships also extend to a wide variety of non-functional sequence elements, including repeats, transposons, pseudogenes, and mutations in protein-coding sequences that do not result in changes in amino-acid sequence. While a minority of these elements might later be found to harbor function, in aggregate they demonstrate that identity must be the product of common descent rather than common function. Finally, a deeper understanding of [[Evolutionary developmental biology|developmental biology]] shows that common morphology is, in fact, the product of shared genetic elements. For example, although camera-like eyes are believed to have evolved independently on many separate occasions, they share a common set of light-sensing proteins ([[opsins]]), suggesting a common point of origin for all sighted creatures. Another noteworthy example is the familiar vertebrate body plan, whose structure is controlled by the homeobox (Hox) family of genes. ==Evidence from paleontology== [[Image:Resin with insect (aka).jpg|thumb|200px|right|An insect trapped in [[amber]].]] When organisms die, they often [[decomposition|decompose]] rapidly or are consumed by [[scavenger]]s, leaving no permanent evidences of their existence. However, occasionally, some organisms are preserved. The remains or [[trace fossil|traces]] of organisms from a past [[geologic time scale|geologic age]] embedded in [[rock (geology)|rocks]] by natural processes are called [[fossil]]s. They are extremely important for understanding the [[timeline of evolution|evolutionary history of life]] on Earth, as they provide direct evidence of evolution and detailed information on the ancestry of organisms. [[Paleontology]] is the study of past life based on fossil records and their relations to different geologic time periods. For fossilization to take place, the traces and remains of organisms must be quickly buried so that [[weathering]] and decomposition do not occur. Skeletal structures or other hard parts of the organisms are the most commonly occurring form of fossilized remains (Paul, 1998), (Behrensmeyer, 1980) and (Martin, 1999). There are also some trace "fossils" showing [[molding (process)|moulds]], cast or imprints of some previous organisms. As an animal dies, the organic materials gradually decay, such that the [[bone]]s become porous. If the animal is subsequently buried in [[mud]], [[mineral]] salts will infiltrate into the bones and gradually fill up the pores. The bones will harden into stones and be preserved as fossils. This process is known as [[petrifaction|petrification]]. If dead animals are covered by wind-blown [[sand]], and if the sand is subsequently turned into mud by heavy [[rain]] or [[flood]]s, the same process of mineral infiltration may occur. Apart from petrification, the dead bodies of organisms may be well preserved in [[ice]], in hardened [[resin]] of [[pinophyta|coniferous]] trees ([[amber]]), in tar, or in anaerobic, [[acid]]ic [[peat]]. Fossilization can sometimes be a trace, an impression of a form. Examples include leaves and footprints, the fossils of which are made in layers that then harden. ===Fossil records=== [[Image:Asaphiscuswheelerii.jpg|thumb|200px|left|Fossil [[trilobite]]. Trilobites were hard-shelled arthropods, related to living [[horseshoe crab]]s and [[spider]]s, that first appeared in significant numbers around 540 [[mya (unit)|mya]], [[extinction|dying out]] 250 mya.]] It is possible to find out how a particular group of organisms evolved by arranging its fossil records in a chronological sequence. Such a sequence can be determined because fossils are mainly found in [[sedimentary rock]]. Sedimentary rock is formed by layers of [[silt]] or mud on top of each other; thus, the resulting rock contains a series of horizontal layers, or [[stratum|strata]]. Each layer contains fossils which are typical for a specific [[period (geology)|time period]] during which they were made. The lowest strata contain the oldest rock and the earliest fossils, while the highest strata contain the youngest rock and more recent fossils. A [[succession]] of animals and plants can also be seen from fossil records. By studying the number and complexity of different fossils at different [[stratigraphy|stratigraphic]] levels, it has been shown that older fossil-bearing rocks contain fewer types of fossilized organisms, and they all have a simpler structure, whereas younger rocks contain a greater variety of fossils, often with increasingly complex structures. In the past, geologists could only roughly estimate the ages of various strata and the fossils found. They did so, for instance, by estimating the time for the formation of sedimentary rock layer by layer. Today, by measuring the proportions of [[radioactive decay|radioactive]] and stable [[chemical element|elements]] in a given rock, the ages of fossils can be more precisely dated by scientists. This technique is known as [[radiometric dating]]. Throughout the fossil record, many species that appear at an early stratigraphic level disappear at a later level. This is interpreted in evolutionary terms as indicating the times at which species originated and became extinct. Geographical regions and climatic conditions have varied throughout the [[History of Earth|Earth's history]]. Since organisms are adapted to particular environments, the constantly changing conditions favoured species which adapted to new environments through the mechanism of [[natural selection]]. According to fossil records, some modern species of plants and animals are found to be almost identical to the species that lived in ancient geological ages. They are existing species of ancient lineages that have remained [[morphology (biology)|morphologically]] (and probably also [[physiology|physiologically]]) somewhat unchanged for a very long time. Consequently, they are called "[[living fossil]]s" by laypeople. Examples of "living fossils" include the [[tuatara]], the [[nautilus]], the [[horseshoe crab]], the [[coelacanth]], the [[ginkgo]], the [[Wollemi pine]], and the [[metasequoia]]. ====Extent of the Fossil Record==== {{seealso|List of transitional fossils}} [[Image:Cynognathus BW.jpg|thumb|250px|right|[[Cynognathus]], a [[Eucynodontia|Eucynodont]], one of a grouping of [[Therapsida|Therapsids]] ("mammal-like reptiles") that is ancestral to all modern mammals.]] Despite the relative rarity of suitable conditions for fossilization, approximately 250,000 fossil species are known[http://www.gpc.edu/~pgore/geology/historical_lab/preservationlab.php]. The number of individual fossils this represents varies greatly from species to species, but many millions of fossils have been recovered: for instance, more than three million fossils from the last [[Ice Age]] have been recovered from the [[La Brea Tar Pits]] in Los Angeles[http://www.tarpits.org/education/guide/index.html]. Many more fossils are still in the ground, in various geological formations known to contain a high fossil density, allowing estimates of the total fossil content of the formation to be made. An example of this occurs in South Africa's Beaufort Formation (part of the [[Karoo Supergroup]], which covers most of South Africa), which is rich in vertebrate fossils, including [[therapsids]] (reptile/mammal [[Transitional fossil|transitional forms]])[http://www.palaeos.com/Paleozoic/Permian/Karroo.htm]. It has been estimated[http://www.lhup.edu/~dsimanek/6flood.htm] that this formation contains 800 billion vertebrate fossils. ===Evolution of the horse=== {{main|Evolution of the horse}} [[Image:Horseevolution.png|275px|thumb|right|[[Evolution of the horse]] showing reconstruction of the fossil species obtained from successive rock strata. The foot diagrams are all front views of the left forefoot. The third [[Metacarpus|metacarpal]] is shaded throughout. The teeth are shown in longitudinal section.]] Due to an almost-complete fossil record found in [[North America]]n sedimentary deposits from the early [[Eocene]] to the present, the [[horse]] provides one of the best examples of evolutionary history ([[phylogeny]]). This evolutionary sequence starts with a small animal called the ''[[Hyracotherium]]'' which lived in North America about 54 million years ago, then spread across to [[Europe]] and [[Asia]]. Fossil remains of ''Hyracotherium'' show it to have differed from the modern horse in three important respects: it was a small animal (the size of a [[fox]]), lightly built and adapted for running; the limbs were short and slender, and the feet elongated so that the digits were almost vertical, with four digits in the [[forelimb]]s and three digits in the [[hindlimb]]s; and the [[incisor]]s were small, the [[Molar (tooth)|molar]]s having low crowns with rounded [[cusp]]s covered in [[Tooth enamel|enamel]]. The probable course of development of horses from ''Hyracotherium'' to ''Equus'' (the modern horse) involved at least 12 [[genus|genera]] and several hundred [[species]]. The major trends seen in the development of the horse to changing environmental conditions may be summarized as follows: * Increase in size (from 0.4&nbsp;m to 1.5&nbsp;m); * Lengthening of limbs and feet; * Reduction of lateral digits; * Increase in length and thickness of the third digit; * Increase in width of [[incisor]]s; * Replacement of [[premolar]]s by [[Molar (tooth)|molar]]s; and * Increases in tooth length, crown height of molars. Fossilized plants found in different strata show that the [[marsh]]y, wooded country in which ''Hyracotherium'' lived became gradually drier. Survival now depended on the head being in an elevated position for gaining a good view of the surrounding countryside, and on a high turn of speed for escape from [[predation|predators]], hence the increase in size and the replacement of the splayed-out foot by the hoofed foot. The drier, harder ground would make the original splayed-out foot unnecessary for support. The changes in the teeth can be explained by assuming that the diet changed from soft [[vegetation]] to [[grass]]. A dominant genus from each geological period has been selected to show the progressive development of the horse. ===Limitations=== The fossil record is an important source for scientists when tracing the evolutionary history of organisms. However, because of limitations inherent in the record, there are not fine scales of intermediate forms between related groups of species. This lack of continuous fossils in the record is a major limitation in tracing the descent of biological groups. Furthermore, there are also much larger gaps between major evolutionary lineages. When [[transitional fossil]]s are found that show intermediate forms in what had previously been a gap in knowledge, they are often popularly referred to as "missing links". There is a gap of about 100 million years between the early [[Cambrian]] period and the later [[Ordovician]] period. The early Cambrian period was the period from which numerous fossils of [[sponge]]s, [[cnidaria]]ns (''e.g.'', [[jellyfish]]), [[echinoderm]]s (''e.g.'', [[eocrinoid]]s), [[mollusca|molluscs]] (''e.g.'', [[snail]]s) and [[arthropod]]s (''e.g.'', [[trilobite]]s) are found. In the later Ordovician period, the first animal that really possessed the typical features of [[vertebrates]], the [[Australia]]n [[fish]], ''[[Arandaspis]]'' appeared. Thus few, if any, fossils of an intermediate type between [[invertebrate]]s and vertebrates have been found, although likely candidates include the [[Burgess Shale]] animal, ''[[Pikaia gracilens]]'', and its [[Maotianshan shales]] relatives, ''[[Myllokunmingia]]'', ''[[Yunnanozoon]]'', ''[[Haikouella lanceolata]]'', and ''[[Haikouichthys]]''. Some of the reasons for the incompleteness of fossil records are: * In general, the probability that an organism becomes fossilized after death is very low; * Some species or groups are less likely to become fossils because they are soft-bodied; * Some species or groups are less likely to become fossils because they live (and die) in conditions that are not favourable for fossilization to occur in; * Many fossils have been destroyed through erosion and tectonic movements; * Some fossil remains are complete, but most are fragmentary; * Some evolutionary change occurs in populations at the limits of a species' ecological range, and as these populations are likely to be small, the probability of fossilization is lower (see [[punctuated equilibrium]]); * Similarly, when environmental conditions change, the population of a species is likely to be greatly reduced, such that any evolutionary change induced by these new conditions is less likely to be fossilized; * Most fossils convey information about external form, but little about how the organism functioned; * Using present-day [[biodiversity]] as a guide, this suggests that the fossils unearthed represent only a small fraction of the large number of species of organisms that lived in the past. ==Evidence from comparative anatomy== [[Comparative anatomy|Comparative study of the anatomy]] of groups of animals or plants reveals that certain structural features are basically similar. For example, the basic structure of all [[flower]]s consists of [[sepal]]s, [[petal]]s, [[Gynoecium|stigma, style and ovary]]; yet the [[size]], [[colour]], [[number]] of parts and specific structure are different for each individual species. ===Homologous structures and divergent (adaptive) evolution=== If widely separated groups of organisms are originated from a common ancestry, they are expected to have certain basic features in common. The degree of [[similarity|resemblance]] between two organisms should indicate how closely related they are in evolution: * Groups with little in common are assumed to have diverged from a [[common ancestor]] much earlier in geological history than groups which have a lot in common; * In deciding how closely related two animals are, a comparative anatomist looks for [[structure]]s that are fundamentally similar, even though they may serve different functions in the [[adult]]. Such structures are described as [[Homology (biology)|homologous]] and suggest a common origin. * In cases where the similar structures serve different functions in adults, it may be necessary to trace their origin and [[Embryogenesis|embryonic development]]. A similar developmental origin suggests they are the same structure, and thus likely to be derived from a common ancestor. When a group of organisms share a homologous structure which is specialized to perform a variety of functions in order to adapt different environmental conditions and modes of life are called [[adaptive radiation]]. The gradual spreading of organisms with adaptive radiation is known as [[divergent evolution]]. ====Pentadactyl limb==== [[Image:Evolution pl.png|thumb|right|500px|'''Figure 5a''': The principle of [[homology (biology)|homology]] illustrated by the adaptive radiation of the forelimb of mammals. All conform to the basic pentadactyl pattern but are modified for different usages. The third metacarpal is shaded throughout; the shoulder is crossed-hatched.]] The pattern of limb bones called [[pentadactyl limb]] is an example of homologous structures (Fig. 5a). It is found in all classes of [[tetrapod]]s (''i.e.'' from [[amphibian]]s to [[mammal]]s). It can even be traced back to the [[fin]]s of certain fossil fishes from which the first amphibians are thought to have evolved. The limb has a single proximal bone ([[humerus]]), two distal bones ([[Radius (bone)|radius]] and [[ulna]]), a series of [[carpal]]s ([[wrist]] bones), followed by five series of metacarpals ([[hand|palm]] bones) and [[phalange]]s (digits). Throughout the tetrapods, the fundamental structures of pentadactyl limbs are the same, indicating that they originated from a common ancestor. But in the course of evolution, these fundamental structures have been modified. They have become superficially different and unrelated structures to serve different functions in adaptation to different environments and modes of life. This phenomenon is clearly shown in the forelimbs of mammals. For example: * In the [[monkey]], the forelimbs are much elongated to form a grasping hand for climbing and swinging among trees. * In the [[pig]], the first digit is lost, and the second and fifth digits are reduced. The remaining two digits are longer and stouter than the rest and bear a hoof for supporting the body. * In the horse, the forelimbs are adapted for support and running by great elongation of the third digit bearing a hoof. * The [[mole (animal)|mole]] has a pair of short, spade-like forelimbs for [[burrowing]]. * The [[anteater]] uses its enlarged third digit for tearing down [[ant]] hills and [[termite]] nests. * In the [[whale]], the forelimbs become [[flipper (anatomy)|flipper]]s for steering and maintaining equilibrium during swimming. * In the [[bat]], the forelimbs have turned into [[wing]]s for flying by great elongation of four digits, while the [[hook]]-like first digit remains free for hanging from [[tree]]s. ====Insect mouthparts==== [[Image:Evolution insect mouthparts.png|thumb|left|250px|'''Figure 5b''': [[Adaptive radiation]] of insect mouthparts: a, [[antenna (biology)|antennae]]; c, [[compound eye]]; lb, labrium; lr, labrum; md, mandibles; mx, maxillae.]] The basic structures are the same, including a [[labrum]] (upper lip), a pair of [[mandible]]s, a [[hypopharynx]] (floor of mouth), a pair of [[maxillae]], and a [[labium (insect)|labium]]. These structures are enlarged and modified; others are reduced and lost. The modifications enable the insects to exploit a variety of food materials (Fig. 5b): (A) Primitive state — biting and chewing: ''e.g.'' [[grasshopper]]. Strong mandibles and maxillae for manipulating food. (B) Ticking and biting: ''e.g.'' [[honey bee]]. Labium long to lap up [[nectar]]; mandibles chew [[pollen]] and mould [[wax]]. (C) Sucking: ''e.g.'' [[butterfly]]. Labrum reduced; mandibles lost; maxillae long forming sucking tube. (D) Piercing and sucking, ''e.g''. [[mosquito|female mosquito]]. Labrum and maxillae form tube; mandibles form piercing stylets; labrum grooved to hold other parts. ====Other arthropod appendages==== Insect mouthparts and antennae are considered homologues of insect legs. Parallel developments are seen in some [[arachnids]]: The anterior pair of legs may be modified as analogues of antennae, particularly in [[uropygid|whip scorpions]], which walk on six legs. These developments provide support for the theory that complex modifications often arise by duplication of components, with the duplicates modified in different directions. ===Analogous structures and convergent evolution=== {{seealso|Evolution of the eye}} [[Image:Evolution eye.png|thumb|right|400px|'''Figure 6''': Inverted retina of vertebrate (left) and non-inverted retina of octopus (right)]] Under similar environmental conditions, fundamentally different structures in different groups of organisms may undergo modifications to serve similar functions. This phenomenon is called [[convergent evolution]]. Similar structures, physiological processes or mode of life in organisms apparently bearing no close phylogenetic links but showing adaptations to perform the same functions are described as [[analogy|analogous]], for example: * Wings of [[bat]]s, [[bird]]s and [[insect]]s; * the jointed legs of [[insect]]s and [[vertebrate]]s; * tail [[fin]] of [[fish]], [[whale]] and [[lobster]]; * [[eye]]s of the [[vertebrate]]s and [[cephalopod]] molluscs ([[squid]] and [[octopus]]). Fig. 6 illustrates difference between an inverted and non-inverted [[retina]], the sensory cells lying beneath the [[nerve fibre]]s. This results in the sensory cells being absent where the [[optic nerve]] is attached to the eye, thus creating a [[blind spot (vision)|blind spot]]. The octopus eye has a non-inverted retina in which the sensory cells lie above the nerve fibres. There is therefore no blind spot in this kind of eye. Apart from this difference the two eyes are remarkably similar, an example of convergent evolution. ===Vestigial structures=== {{Main article|Vestigiality}} A further aspect of comparative anatomy is the presence of vestigial organs. Organs that are smaller and simpler in structure than corresponding parts in the ancestral species are called vestigial organs. They are usually degenerated or underdeveloped. The existence of vestigial organs can be explained in terms of changes in the environment or modes of life of the species. Those organs are thought to be functional in the ancestral species but have now become unnecessary and non-functional. Examples are the vestigial hind limbs of whales, the [[haltere]] (vestigial hind [[wing]]s) of [[fly|flies]] and mosquitos, vestigial wings of flightless birds such as [[ostrich]]es, and the vestigial [[leaf|leaves]] of some [[xerophyte]]s (''e.g.'' [[cactus]]) and [[parasitic plant]]s (''e.g.'' [[Cuscuta|dodder]]). It must be noted, however, that vestigial structures have lost the original function but may have another one. For example the [[halteres]] in [[fly|dipterist]]s help balance the insect while in flight and the wings of ostriches are used in [[mating ritual]]s. ==Evidence from geographical distribution== Data about the presence or absence of species on various [[continent]]s and [[island]]s ([[biogeography]]) can provide evidence of common descent and shed light on patterns of [[speciation]]. ====Continental distribution==== All organisms are adapted to their environment to a greater or lesser extent. If the abiotic and biotic factors within a [[habitat (ecology)|habitat]] are capable of supporting a particular species in one geographic area, then one might assume that the same species would be found in a similar habitat in a similar geographic area, e.g. in [[Africa]] and [[South America]]. This is not the case. Plant and animal species are discontinuously distributed throughout the world: * Africa has short-tailed ([[Old World]]) monkeys, [[elephant]]s, [[lion]]s and [[giraffe]]s. * South America has long-tailed monkeys, [[cougar]]s, [[jaguar]]s and [[llama]]s. Even greater differences can be found if [[Australia]] is taken into consideration, though it occupies the same [[latitude]] as much of South America and Africa. [[Marsupial]]s like the [[kangaroo]], the [[wallaby]], and the [[wombat]] make up over 80 percent of Australia's indigenous mammal population. By contrast, marsupials are totally absent from Africa and are only represented by the [[opossum]] in [[South America]] and the [[Virginia Opossum]] in [[North America]]: * The [[echidna]] and [[platypus]], the only living representatives of primitive egg-laying mammals ([[monotreme]]s), can be found only in Australia and are totally absent in the rest of the world. * On the other hand, Australia has very few [[Eutheria|placental mammals]] and most of these either migrated from elsewhere (e.g. [[bats]]) or were [[Introduced species|introduced]] by human beings (e.g. [[rabbits]]). ====Explanation==== [[Image:Evolution con dis.png|thumb|right|450px|'''Figure 7''': Diagrams to the land bridge between continents in past geological time (A) and the barriers formed (B) due to the submergence of [[land bridge]]s.]] The main groups of modern mammal arose in [[Northern Hemisphere]] and subsequently migrated to three major directions: * to South America via the [[land bridge]] in the [[Bering Strait]] and [[Isthmus of Panama]]; A large number of families of South American marsupials became extinct as a result of competition with these North American counterparts. * to Africa via the [[Strait of Gibraltar]]; and * to Australia via South East Asia to which it was at one time connected by land The shallowness of the Bering Strait would have made the passage of animals between two northern continents a relatively easy matter, and it explains the present-day similarity of the two [[fauna (animals)|fauna]]s. But once they had got down into the southern continents, they presumably became isolated from each other by various types of barriers. *The submersion of the Isthmus of Panama: isolates the South American fauna. *The [[Mediterranean Sea]] and the North African desert: partially isolate the African fauna. *The submersion of the original connection between Australia and South East Asia: isolates the Australian fauna. Once isolated, the animals in each continent have shown adaptive radiation (Fig. 7) to evolve along their own lines. ====Evidence for migration and isolation==== [[Image:Evolution evi mig.png|450px|thumb|right|Map of the world showing distribution of present members of camel. Solid black lines indicate possible migration routes.]] The fossil record for the [[camel]] indicated that evolution of camels started in North America, from which they migrated across the Bering Strait into Asia and hence to Africa, and through the Isthmus of Panama into South America. Once isolated, they evolved along their own lines, giving the modern camel in Asia and Africa and llama in South America. ====Continental drift==== The same kinds of fossils are found from areas known to be adjacent to one another in the past but which, through the process of [[continental drift]], are now in widely divergent geographic locations. For example, fossils of the same types of ancient amphibians, arthropods and ferns are found in South America, Africa, India, Australia and Antarctica, which can be dated to the [[Paleozoic]] Era, at which time these regions were united as a single landmass called [[Gondwana]]. [http://biology.clc.uc.edu/courses/bio303/contdrift.htm] Sometimes the descendants of these organisms can be identified and show unmistakable similarity to each other, even though they now inhabit very different regions and climates. ====Oceanic island distribution==== Most small isolated islands only have native species that could have arrived by air or water; like birds, insects and turtles. The few large mammals present today were brought by human settlers in boats. Plant life on remote and recent volcanic islands like Hawaii could have arrived as airborne spores or as seeds in the droppings of birds. After the explosion of [[Krakatoa]] a century ago and the emergence of a steaming, lifeless remnant island called Anak Krakatoa (child of Krakatoa), plants arrived within months and within a year there were moths and spiders that had arrived by air. The island is now ecologically hard to distinguish from those around it that have been there for millions of years. == Evidence from comparative physiology and biochemistry == {{See also|Archaeogenetics|Common descent|Last universal ancestor|Most recent common ancestor|Nothing in Biology Makes Sense Except in the Light of Evolution|Speciation|Timeline of evolution|Timeline of human evolution|Universal Code (Biology)}} === Universal biochemical organisation === All known extant organisms are based on the same fundamental biochemical organisation: genetic information encoded as nucleic acid ([[DNA]], or [[RNA]] for viruses), transcribed into [[RNA]], then translated into [[proteins]] (that is, polymers of [[amino acids]]) by highly conserved [[ribosomes]]. Perhaps most tellingly, the [[Genetic Code]] (the "translation table" between DNA and amino acids) is the same for almost every organism, meaning that a piece of [[DNA]] in a [[bacteria|bacterium]] codes for the same amino acid as in a human [[cell (biology)|cell]]. [[Adenosine triphosphate|ATP]] is used as energy currency by all extant life. === Molecular variance patterns === A classic example of biochemical evidence for evolution is the variance of the [[protein]] [[Cytochrome c]] in living cells. The variance of cytochrome c of different organisms is measured in the number of differing amino acids, each differing amino acid being a result of a [[base pair]] substitution, a [[mutation]]. If each differing amino acid is assumed to be the result of '''one''' base pair substitution, it can be calculated how long ago the two species diverged by multiplying the number of base pair substitutions by the estimated time it takes for a substituted base pair of the cytochrome c gene to be successfully passed on. For example, if the average time it takes for a base pair of the cytochrome c gene to mutate is N years, the number of amino acids making up the cytochrome c protein in monkeys differ by one from that of humans, this leads to the conclusion that the two species diverged N years ago. Comparison of the DNA sequences allows organisms to be grouped by sequence similarity, and the resulting [[phylogenetics|phylogenetic]] trees are typically congruent with traditional [[taxonomy]], and are often used to strengthen or correct taxonomic classifications. Sequence comparison is considered a measure robust enough to be used to correct erroneous assumptions in the phylogenetic tree in instances where other evidence is scarce. For example, neutral human DNA sequences are approximately 1.2% divergent (based on substitutions) from those of their nearest genetic relative, the [[chimpanzee]], 1.6% from [[gorilla]]s, and 6.6% from [[baboon]]s.<ref>Two sources: 'Genomic divergences between humans and other hominoids and the effective population size of the common ancestor of humans and chimpanzees'. and 'Quantitative Estimates of Sequence Divergence for Comparative Analyses of Mammalian Genomes' "[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11170892] [http://www.genome.org/cgi/content/full/13/5/813]"</ref> Genetic sequence evidence thus allows inference and quantification of genetic relatedness between humans and other [[ape]]s.<ref>The picture labeled "Human Chromosome 2 and its analogs in the apes" in the article [http://www.gate.net/~rwms/hum_ape_chrom.html Comparison of the Human and Great Ape Chromosomes as Evidence for Common Ancestry] is literally a picture of a link in humans that links two separate chromosomes in the nonhuman apes creating a single chromosome in humans. It is considered a missing link, and the ape-human connection is of particular interest. Also, while the term originally referred to fossil evidence, this too is a trace from the past corresponding to some living beings which when alive were the physical embodiment of this link.</ref><ref>The [[New York Times]] report ''[http://www.nytimes.com/2006/03/07/science/07evolve.html Still Evolving, Human Genes Tell New Story]'', based on ''[http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0040072 A Map of Recent Positive Selection in the Human Genome]'', states the [[International HapMap Project]] is "providing the strongest evidence yet that humans are still evolving" and details some of that evidence.</ref> The sequence of the [[16S ribosomal RNA]] gene, a vital gene encoding a part of the [[ribosome]], was used to find the broad phylogenetic relationships between all extant life. The analysis, originally done by [[Carl Woese]], resulted in the [[three-domain system]], arguing for two major splits in the early evolution of life. The first split led to modern [[Bacteria]] and the subsequent split led to modern [[Archaea]] and [[Eukaryote]]. The [[proteome|proteomic]] evidence also supports the universal ancestry of life. Vital [[protein]]s, such as the [[ribosome]], [[DNA polymerase]], and [[RNA polymerase]], are found in everything from the most primitive bacteria to the most complex mammals. The core part of the protein is conserved across all lineages of life, serving similar functions. Higher organisms have evolved additional [[protein subunit]]s, largely affecting the regulation and [[protein-protein interaction]] of the core. Other overarching similarities between all lineages of extant organisms, such as [[DNA]], [[RNA]], amino acids, and the [[lipid bilayer]], give support to the theory of common descent. The [[chirality (chemistry)|chirality]] of DNA, RNA, and amino acids is conserved across all known life. As there is no functional advantage to right- or left-handed molecular chirality, the simplest hypothesis is that the choice was made randomly by early organisms and passed on to all extant life through common descent. Further evidence for reconstructing ancestral lineages comes from [[junk DNA]] such as [[pseudogene]]s, "dead" genes which steadily accumulate mutations.<ref>Pseudogene evolution and natural selection for a compact genome. "[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=10833048]"</ref> There is also a large body of molecular evidence for a number of different mechanisms for large evolutionary changes, among them: [[genome]] and [[gene duplication]], which facilitates rapid evolution by providing substantial quantities of genetic material under weak or no selective constraints; [[horizontal gene transfer]], the process of transferring genetic material to another cell that is not an organism's offspring, allowing for species to acquire beneficial genes from each other; and [[genetic recombination|recombination]], capable of reassorting large numbers of different [[allele]]s and of establishing [[reproductive isolation]]. The [[Endosymbiotic theory]] explains the origin of [[mitochondrion|mitochondria]] and [[plastids]] (''e.g.'' [[chloroplast]]s), which are [[organelle]]s of eukaryotic cells, as the incorporation of an ancient [[prokaryote|prokaryotic]] cell into ancient [[eukaryote|eukaryotic]] cell. Rather than evolving [[eukaryote|eukaryotic]] [[organelle]]s slowly, this theory offers a mechanism for a sudden evolutionary leap by incorporating the genetic material and biochemical composition of a separate species. Evidence supporting this mechanism has recently been found in the [[protist]] [[Hatena]]: as a predator it engulfs a [[green algae]] cell, which subsequently behaves as an [[endosymbiont]], nourishing Hatena, which in turn loses its feeding apparatus and behaves as an [[autotroph]].<ref>{{cite journal| author = Okamoto N, Inouye I. | year =2005| title = A secondary symbiosis in progress| journal =Science | volume =310 | issue =5746 | pages =287| doi = 10.1126/science.1116125| pmid = 16224014}}</ref><ref>{{cite journal| author = Okamoto N | coauthors= Inouye I. | title = Hatena arenicola gen. et sp. nov., a Katablepharid Undergoing Probable Plastid Acquisition.| journal =Protist |volume = 157|issue=4| pages = 401–419| date=October 2006 | doi = 10.1016/j.protis.2006.05.011}}</ref> Since [[metabolism|metabolic]] processes do not leave fossils, research into the evolution of the basic cellular processes is done largely by comparison of existing organisms. Many lineages diverged when new metabolic processes appeared, and it is theoretically possible to determine when certain metabolic processes appeared by comparing the traits of the descendants of a common ancestor or by detecting their physical manifestations. As an example, the appearance of [[oxygen]] in the [[earth's atmosphere]] is linked to the evolution of [[photosynthesis]]. ===Out of Africa hypothesis of human evolution=== {{Main article|Recent single-origin hypothesis}} Mathematical models of evolution, pioneered by the likes of [[Sewall Wright]], [[Ronald Fisher]] and [[J. B. S. Haldane]] and extended via [[diffusion equation|diffusion theory]] by [[Motoo Kimura]], allow predictions about the genetic structure of evolving populations. Direct examination of the genetic structure of modern populations via DNA sequencing has recently allowed verification of many of these predictions. For example, the [[Recent single-origin hypothesis|Out of Africa]] theory of human origins, which states that modern humans developed in Africa and a small sub-population migrated out (undergoing a [[population bottleneck]]), implies that modern populations should show the signatures of this migration pattern. Specifically, post-bottleneck populations (Europeans and Asians) should show lower overall genetic diversity and a more uniform distribution of allele frequencies compared to the African population. Both of these predictions are borne out by actual data from a number of studies.{{Fact|date=February 2007}} ==Evidence from antibiotic and pesticide resistance== The development and spread of [[antibiotic resistance|antibiotic resistant]] [[bacteria]], like the spread of [[pesticide]] resistant forms of plants and insects is evidence for evolution of species, and of change within species. Thus the appearance of [[vancomycin]] resistant ''[[Golden staph|Staphylococcus aureus]]'', and the danger it poses to hospital patients is a direct result of evolution through natural selection. The rise of ''[[Shigella]]'' strains resistant to the synthetic antibiotic class of [[sulfonamides]] also demonstrates the generation of new information as an evolutionary process<ref>{{cite journal| author = Tanaka T, Hashimoto H. | year =1989| title = Drug-resistance and its transferability of Shigella strains isolated in 1986 in Japan| journal =Kansenshogaku Zasshi | volume =63 | issue =1 | pages =15–26}}</ref>. Similarly, the appearance of [[DDT]] resistance in various forms of [[Anopheles]] mosquitoes, and the appearance of [[myxomatosis]] resistance in breeding rabbit populations in Australia, are all evidence of the existence of evolution in situations of evolutionary [[selection pressure]] in species in which generations occur rapidly. ==Evidence from studies of complex iteration== "It has taken more than five decades, but the electronic computer is now powerful enough to simulate evolution" [http://www.trnmag.com/Stories/2003/052103/Simulated_evolution_gets_complex_052103.html] assisting [[bioinformatics]] in its attempt to solve biological problems. [[Computer science]] allows the [[iteration]] of self changing [[complex system]]s to be studied, allowing a mathematical understanding of the nature of the processes behind evolution; providing evidence for the hidden causes of known evolutionary events. The evolution of specific cellular mechanisms like [[spliceosome]]s that can turn the cell's genome into a vast workshop of billions of interchangeable parts that can create tools that create tools that create tools that create us can be studied for the first time in an exact way. For example, Christoph Adami ''et al.'' make this point in ''Evolution of biological complexity'': :To make a case for or against a trend in the evolution of complexity in biological evolution, complexity needs to be both rigorously defined and measurable. A recent information-theoretic (but intuitively evident) definition identifies genomic complexity with the amount of information a sequence stores about its environment. We investigate the evolution of genomic complexity in populations of digital organisms and monitor in detail the evolutionary transitions that increase complexity. We show that, because natural selection forces genomes to behave as a natural "[[Maxwell's Demon|Maxwell Demon]]," within a fixed environment, genomic complexity is forced to increase. [http://www.pnas.org/cgi/content/full/97/9/4463] For example, David J. Earl and Michael W. Deem make this point in ''Evolvability is a selectable trait'': :Not only has life evolved, but life has evolved to evolve. That is, correlations within protein structure have evolved, and mechanisms to manipulate these correlations have evolved in tandem. The rates at which the various events within the hierarchy of evolutionary moves occur are not random or arbitrary but are selected by Darwinian evolution. Sensibly, rapid or extreme environmental change leads to selection for greater evolvability. This selection is not forbidden by causality and is strongest on the largest-scale moves within the mutational hierarchy. Many observations within evolutionary biology, heretofore considered evolutionary happenstance or accidents, are explained by selection for evolvability. For example, the vertebrate immune system shows that the variable environment of antigens has provided selective pressure for the use of adaptable codons and low-fidelity polymerases during [[somatic hypermutation]]. A similar driving force for biased codon usage as a result of productively high mutation rates is observed in the hemagglutinin protein of [[Influenzavirus A|influenza A]]. [http://www.pnas.org/cgi/content/full/101/32/11531] "Computer simulations of the evolution of linear sequences have demonstrated the importance of recombination of blocks of sequence rather than point mutagenesis alone. Repeated cycles of point mutagenesis, recombination, and selection should allow ''in vitro'' molecular evolution of complex sequences, such as proteins." [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=45099] Evolutionary molecular engineering, also called directed evolution or ''in vitro'' molecular evolution involves the iterated cycle of mutation, multiplication with recombination, and selection of the fittest of individual molecules (proteins, DNA, and RNA). Natural evolution can be relived showing us possible paths from catalytic cycles based on proteins to based on RNA to based on DNA. [http://www.scripps.edu/newsandviews/e_20060327/evo.html] [http://bio.kaist.ac.kr/~jsrhee/research03.html] [http://www.isgec.org/gecco-2005/free-tutorials.html#ivme] [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=45099] ==Evidence from speciation== ===Hawthorn fly=== One example of evolution at work is the case of the hawthorn fly, ''[[Rhagoletis pomonella]]'', also known as the apple maggot fly, which appears to be undergoing [[sympatric speciation]].<ref>{{cite journal| author =Feder ''et al'' | year =2003| title = Evidence for inversion polymorphism related to sympatric host race formation in the apple maggot fly, Rhagoletis pomonella.| journal =Genetics | volume =163 | issue =3|pages =939–953}}</ref> Different populations of hawthorn fly feed on different fruits. A distinct population emerged in North America in the 19th century some time after [[apples]], a non-native species, were introduced. This apple-feeding population normally feeds only on apples and not on the historically preferred fruit of [[Crataegus|hawthorns]]. The current hawthorn feeding population does not normally feed on apples. Some evidence, such as the fact that six out of thirteen [[allozyme]] loci are different, that hawthorn flies mature later in the season and take longer to mature than apple flies; and that there is little evidence of interbreeding (researchers have documented a 4-6% hybridization rate) suggests that this is occurring. The emergence of the new hawthorn fly is an example of evolution in progress.<ref>Berlocher, S.H. and G.L. Bush. 1982. An electrophoretic analysis of Rhagoletis (Diptera: Tephritidae) phylogeny. Systematic Zoology 31:136-155; Berlocher, S.H. and J.L. Feder. 2002. Sympatric speciation in phytophagous insects: moving beyond controversy? Annual Review of Entomology 47:773-815; Bush, G.L. 1969. Sympatric host race formation and speciation in frugivorous flies of the genus Rhagoletis (Diptera: Tephritidae). Evolution 23:237-251; Prokopy, R.J., S.R. Diehl and S.S. Cooley. 1988. Behavioral evidence for host races in Rhagoletis pomonella flies. [[Oecologia]] 76:138-147. [http://www.pnas.org/cgi/content/full/94/21/11417 Proc. Natl. Acad. Sci. USA - Vol. 94, pp. 11417-11421, October 1997 - Evolution] article Selective maintenance of allozyme differences among sympatric host races of the apple maggot fly.</ref> ==See also== *[[Human history]] *[[Objections to evolution]] ==References== {{reflist}} {{refbegin}} *Darwin, Charles [[November 24]] [[1859]]. ''On the [[Origin of Species]] by means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life''. London: [[John Murray (publisher)|John Murray]], [[Albemarle Street]]. 502 pages. Reprinted: Gramercy (May 22, 1995). ISBN 0-517-12320-7 *Mayr, Ernst. ''What Evolution Is''. Basic Books (October, 2002). ISBN 0-465-04426-3 *Gigerenzer, Gerd, ''et al.'', ''The empire of chance: how probability changed science and everyday life'' (New York: Cambridge University Press, 1989). *Williams, G.C. (1966). Adaptation and Natural Selection: A Critique of some Current Evolutionary Thought. Princeton, N.J.: Princeton University Press. *''Biological science'', Oxford, 2002. *CJ Clegg, 1999, ''Genetics and Evolution'', John Murray. ISBN 0-7195-7552-4 *Y.K. Ho, 2004, ''Advanced-level Biology for Hong Kong'', Manhattan Press. ISBN 962-990-635-X *Paul, Christopher R. C. (1998) ''The Adequacy of the Fossil Record'', John Wiley & Sons, ISBN 0-471-96988-5 *Behrensmeyer, Anna K. (1980) ''Fossils in the making: Vertebrate taphonomy and paleoecology'', University of Chicago Press, ISBN 0-226-04169-7 *Martin, Ronald E. ''et al.'' eds. (1999) ''Taphonomy: A Process Approach'', Cambridge University Press, ISBN 0-521-59833-8 {{refend}} ==External links== * [http://www.talkorigins.org/faqs/comdesc/ 29+ Evidences for Macroevolution: The Scientific Case for Common Descent] * [http://nationalacademies.org/evolution/ National Academies Evolution Resources] * [http://www.chains-of-reason.org/chains/evolution-by-natural-selection/introduction.htm Evolution by Natural Selection] — An introduction to the logic of the theory of evolution by natural selection * [http://www.pbs.org/wgbh/evolution/index.html Evolution] — Provided by ''[[Public Broadcasting Service|PBS]]''. * [http://science.howstuffworks.com/evolution.htm/printable Howstuffworks.com — How Evolution Works] * [http://www.genomenewsnetwork.org/categories/index/genome/evolution.php Evolution News from Genome News Network (GNN)] * [http://www.nap.edu/books/0309063647/html/ National Academy Press: Teaching About Evolution and the Nature of Science] * [http://www.talkorigins.org/faqs/faq-transitional.html Transitional Vertebrate Fossils FAQ] {{evolution}} <!-- Categorization --> [[Category:Creationist objections to evolution]] [[Category:Evolutionary biology]] [[Category:Theories]] [[nl:Wetenschappelijk bewijs voor de evolutietheorie]] [[pt:Evidências da evolução]]