Organism
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{{Taxobox | color = limegreen
| name = '''Life on Earth'''
| fossil_range = Late [[Hadean]] - Recent
| image = EscherichiaColi NIAID.jpg
| image_width = 240px
| image_caption = These ''[[Escherichia coli]]'' cells provide an example of a [[prokaryote|prokaryotic]] [[microorganism]]
| unranked_classis = [[Life on Earth]] (''Gaeabionta'')
|subdivision_ranks = [[Domain (biology)|Domain]]s and [[Kingdom (biology)|Kingdom]]s
| subdivision =
*[[Nanobes]] [[non-life|<span title="Whether nanobes should be considered as life is disputed."><sup>?</sup></span>]]
*[[Non-cellular life|Acytota]] [[Paraphyly|<span title="Acytota may be paraphyletic as the 'evolution' of viruses and other similar forms is still certain, cellular life might have evolved from non-cellular life.">*</span>]][[Polyphyly|<span title="Acytota may be polyphyletic as the 'evolution' of viruses and other similar forms is still uncertain, the most recent common ancestor might not be included.">*</span>]][[non-life|<span title="Whether viruses and other similar forms should be considered as life is disputed."><sup>?</sup></span>]]
*[[Cellular life|Cytota]]
**[[Bacteria]] [[Paraphyly|<span title="Bacteria may be paraphyletic: Cavalier-Smith has recently proposed that Neomura evolved from Bacteria.">*</span>]]
**[[Neomura]]
***[[Archaea]]
***[[Eukaryota]]
****[[Bikonta]]
*****[[Apusozoa]]
*****[[Rhizaria]]
*****[[Excavata]]
*****[[Archaeplastida]]
******[[Rhodophyta]]
******[[Glaucophyta]]
******'''[[Plantae]]'''
*****[[Heterokontophyta]]
*****[[Haptophyta]]
*****[[Cryptophyta]]
*****[[Alveolata]]
****[[Unikonta]]
*****[[Amoebozoa]]
*****[[Opisthokonta]]
******[[Choanozoa]]
******'''[[Fungi]]'''
******'''[[Animalia]]'''
}}
[[Image:Ericoid mycorrhizal fungus.jpg|thumb|right|200px|An ericoid mycorrhizal [[fungus]]]]
{{Redirect|Life on Earth||Life on Earth (TV series)}}
In [[biology]], an '''organism''' is an individual [[life|living]] system (such as animal, plant, fungus, or micro-organism). In at least some form, all organisms are capable of reacting to stimuli, reproduction, growth and maintenance as a stable whole (after FAO<ref name=FAO>[http://www.fao.org/biotech/find-formalpha-n.asp Biotechnology in Food and Agriculture<!-- Bot generated title -->]</ref>). An organism may be [[unicellular]] or made up, as in humans, of many billions of [[cell (biology)|cell]]s grouped into specialized [[Tissue (biology)|tissues]] and [[organs]]. The phrase ''[[multicellular organism|complex organism]]'' describes any organism with more than one [[cell (biology)|cell]].
The term "organism" ([[Greek language|Greek]] ''οργανισμός'' - ''organismos'', from [[Ancient Greek]] ''όργανον'' - ''organon'', "organ, instrument, tool") first appeared in the English language in 1701 and took on its current definition by 1834 (Oxford English Dictionary).
Organisms may be divided into the [[prokaryote|prokaryotic]] and [[eukaryote|eukaryotic]] groups. The prokaryotes represent two separate [[Three-domain system|domains]], the [[Bacterium|Bacteria]] and [[Archaea]].<ref name=cavaliersmith1987>T.Cavalier-Smith (1987) The origin of eukaryote and archaebacterial cells, Annals of the New York Academy of Sciences 503, 17–54</ref> All [[fungi]], [[animals]] and [[plants]] are eukaryotes.
The word "'''''organism'''''" may broadly be defined as ''an assembly of molecules that function as a more or less stable whole and has the properties of life.'' However, many sources propose definitions that exclude [[virus]]es and theoretically-possible man-made [[alternative biochemistry|non-organic life]] forms.<ref name=OED>{{cite encyclopedia | encyclopedia=Oxford English Dictionary | edition=online | year=2004 | title=organism}}</ref> Viruses are dependent on the biochemical machinery of a host cell for reproduction.
[[Chambers Online Reference]] provides a broad definition: "any living structure, such as a plant, animal, fungus or bacterium, capable of growth and reproduction"<ref name=Chambers>{{cite encyclopedia | encyclopedia=Chambers 21st Century Dictionary | edition=online | year=1999 | title=organism}}</ref>.
In multicellular life the word "organism" usually describes the whole hierarchical assemblage of systems (for example [[circulatory system|circulatory]], [[digestive system|digestive]], or [[reproductive system|reproductive]]) themselves collections of [[organ (anatomy)|organ]]s; these are, in turn, collections of tissues, which are themselves made of [[cell (biology)|cell]]s. In some plants and the [[nematode]] ''[[Caenorhabditis elegans]]'', individual cells are [[totipotent]].[[Image:Fungi in Borneo.jpg|thumb|left|A [[polypores]] [[mushroom]] has [[parasitic]] relationship with this [[Birch Tree]]]]
[[Image:Herpes simpex virus.jpg|125px|thumb|right|Herpes simplex virus]]
===Viruses===
[[Virus]]es are not typically considered to be organisms because they are incapable of "independent" [[reproduction]] or [[metabolism]]. This controversy is problematic, though, since some [[parasite]]s and [[endosymbiont]]s are also incapable of independent life. Although viruses have a few [[enzyme]]s and molecules characteristic of living organisms, they are incapable of reproducing outside a [[cell (biology)|host cell]] and most of their metabolic processes require a host and its 'genetic machinery' such as [[organelle]]s in eukaryotic hosts and the assemblage of ready-made enzymes (which the virus cannot make by itself) in prokaryotic hosts. While viruses sustain no independent [[metabolism]], and thus are usually not accounted organisms, they do have their own [[gene]]s and they do [[evolve|evolution]] by the same mechanisms by which organisms evolve.
===Superorganism===
{{main|Superorganism}}
A superorganism is an organism consisting of many organisms. This is usually meant to be a social [[Units of measurement|unit]] of [[eusociality|eusocial]] animals, where [[division of labour]] is highly specialized and where individuals are not able to survive by themselves for extended periods of time. [[Ant]]s are the most well known example of such a superorganism. [[Thermoregulation]], a feature usually exhibited by individual organisms, does not occur in individuals or small groups of [[honeybee]]s of the species ''[[Apis mellifera]]''. When these bees pack together in clusters of between 5000 and 40000, the colony can thermoregulate.<ref>{{cite journal
| last = Southwick
| first = Edward E.
| year = 1983
| title = The honey bee cluster as a homeothermic superorganism
| journal = Comparative Biochemistry and Physiology
| volume = 75A
| issue = 4
| pages = 741–745
| doi =10.1016/0300-9629(83)90434-6
| url =http://www.sciencedirect.com/science?_ob=MiamiImageURL&_imagekey=B6T2P-4867WXH-110-2&_cdi=4924&_user=4385511&_check=y&_orig=search&_coverDate=12%2F31%2F1983&_qd=1&view=c&wchp=dGLbVlz-zSkWW&md5=d23bd1cec870de7f5a44f8a2f367ed9c&ie=/sdarticle.pdf
| format = PDF
| accessdate = 2006-07-20
}}</ref> [[James Lovelock]], with his "[[Gaia Theory]]" has paralleled the work of [[Vladimir Vernadsky]], who suggested the whole of the [[biosphere]] in some respects can be considered as a superorganism.
[[Image:Elephant-ear-sponge.jpg|thumb|left|A [[sea sponge]] is a very simple type of [[multicellular organism]]]]
The concept of superorganism is under dispute, as many [[biology|biologists]] maintain that in order for a social unit to be considered an organism by itself, the individuals should be in permanent physical connection to each other, and its [[evolution]] should be governed by selection to the whole society instead of individuals. While it's generally accepted that the society of eusocial animals is a unit of [[natural selection]] to at least some extent, most [[evolutionist]]s claim that the individuals are still the primary units of selection.
The question remains "What is to be considered ''the [[individualism|individual]]''?". [[Darwinism|Darwinians]] like [[Richard Dawkins]] suggest that the individual selected is the "[[Selfish Gene]]". Others believe it is the whole genome of an organism. [[E.O. Wilson]] has shown that with ant-colonies and other social [[insects]] it is the breeding entity of the colony that is selected, and not its individual members. This could apply to the bacterial members of a [[stromatolite]], which, because of genetic sharing, in some way comprise a single [[gene pool]]. Gaian theorists like [[Lynn Margulis]] would argue this applies equally to the [[symbiogenesis]] of the bacterial underpinnings of the whole of the Earth.
It would appear, from computer [[simulation]]s like [[Daisyworld]] that biological [[natural selection|selection]] occurs at multiple levels simultaneously.
It is also argued that humans are actually a superorganism that includes microorganisms such as [[bacteria]]. It is estimated that "the human intestinal microbiota is composed of 10<sup>13</sup> to 10<sup>14</sup> microorganisms whose collective [[genome]] ("microbiome") contains at least 100 times as many genes as our own[...] Our microbiome has significantly enriched metabolism of [[glycan]]s, [[amino acid]]s, and [[xenobiotic]]s; [[methanogenesis]]; and 2-methyl-D-erythritol 4-phosphate pathway–mediated biosynthesis of vitamins and [[isoprenoid]]s. Thus, humans are superorganisms whose metabolism represents an amalgamation of microbial and human attributes." <ref>Gill S. R., et al. ''Science'', ''312'', 1355-1359 ('''2006'''). http://dx.doi.org/10.1126/science.1124234</ref>. An [[NIH]]-coordinated and -funded effort is currently in progress to characterize the [[Human microbiome project|human microbiome]].
==Organizational terminology==
All organisms are classified by the science of [[alpha taxonomy]] into either [[taxa]] or [[clades]].
Taxa are ranked groups of organisms which run from the general ([[domain (biology)|domain]]) to the specific ([[species]]). A broad scheme of ranks in hierarchical order is:
* [[Domain (biology)|Domain]]
* [[Kingdom (biology)|Kingdom]]
* [[Phylum]]
* [[Class (biology)|Class]]
* [[Order (biology)|Order]]
* [[Family (biology)|Family]]
* [[Genus]]
* [[Species]]
To give an example, ''[[Homo sapiens]]'' is the [[Latin binomial]] equating to modern humans. All members of the species ''sapiens'' are, at least in theory, genetically able to interbreed. Several species may belong to a genus, but the members of different species within a genus are unable to interbreed to produce fertile offspring. [[Homo (genus)|Homo]], however, only has one surviving species (sapiens); ''[[Homo erectus]]'', ''[[Homo neanderthalensis]]'', &c. having become extinct thousands of years ago. Several genera belong to the same family and so on up the hierarchy. Eventually, the relevant kingdom ([[Animalia]], in the case of humans) is placed into one of the three domains depending upon certain genetic and structural characteristics.
All living organisms known to science are given classification by this system such that the species within a particular family are more closely related and genetically similar than the species within a particular phylum.
[[Image:Blue crab on market in Piraeus - Callinectes sapidus Rathbun 20020819-317.jpg|thumb|200 px|A [[crab]] is an example of an organism.]]
==Chemistry==
Organisms are complex chemical systems, organized in ways that promote reproduction and some measure of sustainability or survival. The molecular phenomena of chemistry are fundamental in understanding organisms, but it is a philosophical error (reductionism) to reduce organismal biology to mere chemistry. It is generally the phenomena of entire organisms that determine their fitness to an environment and therefore the survivability of their DNA based genes.
Organisms clearly owe their origin, metabolism, and many other internal functions to chemical phenomena, especially the chemistry of large organic molecules. Organisms are complex systems of [[chemical compound]]s which, through interaction with each other and the environment, play a wide variety of roles.
Organisms are semi-closed chemical systems. Although they are individual units of life (as the definition requires) they are not closed to the environment around them. To operate they constantly take in and release energy. [[Autotroph]]s produce usable energy (in the form of organic compounds) using light from the sun or inorganic compounds while [[heterotroph]]s take in organic compounds from the environment.
The primary [[chemical element]] in these compounds is [[carbon]]. The physical properties of this element such as its great affinity for bonding with other small atoms, including other carbon atoms, and its small size makes it capable of forming multiple bonds, make it ideal as the basis of organic life. It is able to form small compounds containing three atoms (such as [[carbon dioxide]]) as well as large chains of many thousands of atoms which are able to store data ([[nucleic acid]]s), hold cells together and transmit information ([[protein]]).
===Macromolecules===
The compounds which make up organisms may be divided into [[macromolecule]]s and other, smaller molecules. The four groups of macromolecule are [[nucleic acid]]s, [[protein]]s, [[carbohydrate]]s and [[lipid]]s. Nucleic acids (specifically [[deoxyribonucleic acid]], or DNA) store genetic data as a sequence of [[nucleotide]]s. The particular sequence of the four different types of nucleotides ([[adenine]], [[cytosine]], [[guanine]], and [[thymine]]) dictate the many characteristics which constitute the organism. The sequence is divided up into [[codon]]s, each of which is a particular sequence of three nucleotides and corresponds to a particular [[amino acid]]. Thus a sequence of DNA codes for a particular protein which, due to the chemical properties of the amino acids of which it is made, [[protein folding|folds]] in a particular manner and so performs a particular function.
The following functions of protein have been recognized:
# [[Enzyme]]s, which catalyze all of the reactions of metabolism;
# Structural proteins, such as [[tubulin]], or [[collagen]];
# Regulatory proteins, such as [[transcription factors]] or cyclins that regulate the cell cycle;
# Signaling molecules or their receptors such as some [[hormones]] and their receptors;
# Defensive proteins, which can include everything from [[antibodies]] of the [[immune system]], to toxins (e.g., [[dendrotoxin]]s of snakes), to proteins that include unusual amino acids like [[canavanine]].
Lipids make up the [[phospholipid membrane|membrane]] of cells which constitutes a barrier, containing everything within the cell and preventing compounds from freely passing into, and out of, the cell. In some multi-cellular organisms they serve to store energy and mediate communication between cells. Carbohydrates also store and transport energy in some organisms, but are more easily broken down than lipids.
==Structure==
All organisms consist of monomeric units called [[cell (biology)|cell]]s; some contain a single cell ([[unicellular]]) and others contain many units ([[multicellular]]). Multicellular organisms are able to specialize cells to perform specific functions, a group of such cells is [[biological tissue|tissue]] the four basic types of which are [[epithelium]], [[nervous tissue]], [[muscle|muscle tissue]] and [[connective tissue]]. Several types of tissue work together in the form of an [[organ (anatomy)|organ]] to produce a particular function (such as the pumping of the blood by the [[heart]], or as a barrier to the environment as the [[skin]]). This pattern continues to a higher level with several organs functioning as an [[organ system]] to allow for [[reproductive system|reproduction]], [[digestive system|digestion]], &c. Many multicelled organisms comprise of several organ systems which coordinate to allow for life.
===The cell===
The [[cell theory]], first developed in 1839 by [[Matthias Jakob Schleiden|Schleiden]] and [[Theodor Schwann|Schwann]], states that all organisms are composed of one or more cells; all cells come from preexisting cells; all vital functions of an organism occur within cells, and cells contain the [[genetics|hereditary information]] necessary for regulating cell functions and for transmitting information to the next generation of cells.
There are two types of cells, eukaryotic and prokaryotic. Prokaryotic cells are usually singletons, while eukaryotic cells are usually found in multi-cellular organisms. Prokaryotic cells lack a [[nuclear membrane]] so [[DNA]] is unbound within the cell, eukaryotic cells have nuclear membranes.
All cells, whether [[prokaryotic]] or [[eukaryotic]], have a [[cell membrane|membrane]], which envelopes the cell, separates its interior from its environment, regulates what moves in and out, and maintains the [[cell potential|electric potential of the cell]]. Inside the membrane, a [[salt]]y [[cytoplasm]] takes up most of the cell volume. All cells possess [[DNA]], the hereditary material of [[gene]]s, and [[RNA]], containing the information necessary to [[gene expression|build]] various [[protein]]s such as [[enzyme]]s, the cell's primary machinery. There are also other kinds of [[biomolecule]]s in cells.
All cells share several abilities<ref name="AlbertsCh1">[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=GenBookHL&term=%22all+cells%22+AND+mboc4%5Bbook%5D+AND+372023%5Buid%5D&rid=mboc4.section.4#23 The Universal Features of Cells on Earth] in Chapter 1 of ''[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=GenBookHL&term=cell+biology+AND+mboc4%5Bbook%5D+AND+373693%5Buid%5D&rid=mboc4 Molecular Biology of the Cell]'' fourth edition, edited by Bruce Alberts (2002) published by Garland Science.</ref>:
* Reproduction by [[cell division]] ([[binary fission]], [[mitosis]] or [[meiosis]]).
* Use of [[enzyme]]s and other [[protein]]s [[genetic code|coded for]] by [[DNA]] [[gene]]s and made via [[messenger RNA]] intermediates and [[ribosome]]s.
* [[Metabolism]], including taking in raw materials, building cell components, converting [[energy]], [[molecule]]s and releasing [[by-product]]s. The functioning of a cell depends upon its ability to extract and use chemical energy stored in organic molecules. This energy is derived from [[metabolic pathway]]s.
* Response to external and internal [[Signal transduction|stimuli]] such as changes in temperature, [[pH]] or nutrient levels.
* Cell contents are contained within a [[Cell membrane|cell surface membrane]] that contains proteins and a [[lipid bilayer]].
==Life span==
One of the basic parameters of organism is its [[life span]]. Some organisms live as short as one day, while some plants can live thousands of years. [[Senescence|Aging]] is important when determining life span of most organisms, bacterium, a virus or even a [[prion]].{{Fact|date=April 2008}}
==Evolution==
{{seealso|Common descent|Origin of life}}
[[Image:Phylogenetic tree.svg|thumb|350px|left|A hypothetical [[phylogenetic tree]] of all extant organisms, based on 16S [[non-coding RNA|rRNA]] [[gene]] sequence data, showing the evolutionary history of the [[Three-domain system|three domains of life]], [[bacteria]], [[archaea]] and [[eukaryote]]s. Originally proposed by [[Carl Woese]].]]
In biology, the theory of [[universal common descent]] proposes that all organisms on Earth are descended from a common ancestor or ancestral gene pool.
Evidence for common descent may be found in traits shared between all living organisms. In Darwin's day, the evidence of shared traits was based solely on visible observation of morphologic similarities, such as the fact that all birds have wings, even those which do not fly. Today, there is strong evidence from genetics that all organisms have a common ancestor. For example, every living cell makes use of [[nucleic acid]]s as its genetic material, and uses the same twenty [[amino acid]]s as the building blocks for [[protein]]s. The universality of these traits strongly suggests either common ancestry or intelligent design.
The "Last Universal Ancestor" is the name given to the [[hypothetical]] [[unicellular|single cellular]] [[organisms|organism]] or single cell that gave rise to all [[life on Earth]] 3.9 to 4.1 billion years ago; however, this hypothesis has since been refuted on many grounds. For example, it was once thought that the [[genetic code]] was universal (see: [[universal genetic code]]), but differences in the genetic code and differences in how each organism translates nucleic acid sequences into proteins, provide support that there never was any "last universal common ancestor." Back in the early 1970s, evolutionary biologists thought that a given piece of [[DNA]] specified the same [[protein subunit]] in every living thing, and that the genetic code was thus universal. Since this is something unlikely to happen by chance, it was interpreted as evidence that every organism had [[inherited]] its genetic code from a single common ancestor, aka., the "Last Universal Ancestor." In 1979, however, exceptions to the code were found in mitochondria, the tiny energy factories inside cells. Biologists subsequently found exceptions in [[bacteria]] and in the [[Cell nucleus|nuclei]] of [[algae]] and single-celled animals. It is now clear that the genetic code is not the same in all living things, and that it does not provide powerful evidence that all living things evolved on a single tree of life.<ref>{{cite journal|last=Edwards|first=Mark|url=http://www.arn.org/docs/pbsevolution/pbsfalseclaim091001.htm|title=PBS Charged with "False Claim" on "Universal Genetic Code.|journal=Science, TV Review, & Education Writers|date=2001|accessdate=2007-03-20}}</ref> Further support that there is no "Last Universal Ancestor" has been provided over the years by [[Horizontal gene transfer#Evolutionary theory|Lateral gene transfer]] in both [[prokaryote]] and [[eukaryote]] single cell organisms. This is why [[phylogenetic trees]] cannot be rooted, why almost all phylogenetic trees have different branching structures, particularly near the base of the tree, and why many organisms have been found with [[codons]] and sections of their [[DNA sequence]] that are unrelated to any other species.
Information about the early development of life includes input from the fields of geology and [[planetary science]]. These sciences provide information about the history of the Earth and the changes produced by life. However, a great deal of information about the early Earth has been destroyed by geological processes over the course of time.
<br style="clear:both;">
===History of life===
<!-- for future reference, heh, here's a ref to stromatolite debate that I took out because it messed up formatting -
"Ancient microfossils from Western Australia are again the subject of heated scientific argument: are they the oldest sign of life on Earth, or just a flaw in the rock?" "[http://www.abc.net.au/science/news/space/SpaceRepublish_497964.htm]" -->
{{main|Timeline of evolution}}
The [[chemical evolution]] from [[Catalyst|self-catalytic chemical reactions]] to [[life]] (see [[Origin of life]]) is not a part of biological evolution, but it is unclear at which point such increasingly complex sets of reactions became what we would consider, today, to be living organisms.
[[Image:Stromatolites.jpg|right|thumb|280px|[[Precambrian]] [[stromatolite]]s in the Siyeh Formation, [[Glacier National Park (U.S.)|Glacier National Park]]. In 2002, William Schopf of [[University of California, Los Angeles|UCLA]] published a controversial paper in the journal ''[[Nature (journal)|Nature]]'' arguing that formations such as this possess 3.5 billion year old [[fossil]]ized [[algae]] microbes. If true, they would be the earliest known life on earth.]]
Not much is known about the earliest developments in life. However, all existing organisms share certain traits, including cellular structure and [[genetic code]]. Most scientists interpret this to mean all existing organisms share a common ancestor, which had already developed the most fundamental cellular processes, but there is no [[scientific consensus]] on the relationship of the three domains of life ([[Archaea]], [[Bacterium|Bacteria]], [[Eukaryota]]) or the [[origin of life]]. Attempts to shed light on the earliest history of life generally focus on the behavior of [[macromolecule]]s, particularly [[RNA]], and the behavior of [[complex system]]s.
The emergence of oxygenic [[photosynthesis]] (around 3 billion years ago) and the subsequent emergence of an oxygen-rich, non-reducing atmosphere can be traced through the formation of [[Banded iron formation|banded iron]] deposits, and later [[red bed]]s of iron oxides. This was a necessary prerequisite for the development of [[aerobic respiration|aerobic]] [[cellular respiration]], believed to have emerged around 2 billion years ago.
In the last billion years, simple multicellular plants and animals began to appear in the oceans. Soon after the emergence of the first animals, the [[Cambrian explosion]] (a period of unrivaled and remarkable, but brief, organismal diversity documented in the fossils found at the [[Burgess Shale]]) saw the creation of all the major body plans, or [[phylum (biology)|phyla]], of modern animals. This event is now believed to have been triggered by the development of the [[Homeobox|Hox genes]]. About 500 million years ago, [[plant]]s and [[fungi]] colonized the land, and were soon followed by [[arthropod]]s and other animals, leading to the development of land [[ecosystem]]s with which we are familiar.
The evolutionary process may be exceedingly slow. Fossil evidence indicates that the diversity and complexity of modern life has developed over much of the [[history of Earth|history of the earth]]. [[geology|Geological]] evidence indicates that the Earth is approximately [[Age of the Earth|4.6 billion years old]]. Studies on guppies by David Reznick at the University of California, Riverside, however, have shown that the rate of evolution through natural selection can proceed 10 thousand to 10 million times faster than what is indicated in the fossil record.<ref>Evaluation of the Rate of Evolution in Natural Populations of Guppies (Poecilia reticulata) "[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=9072971&query_hl=2]"</ref>. Such comparative studies however are invariably biased by disparities in the time scales over which evolutionary change is measured in the laboratory, field experiments, and the fossil record.
===Horizontal gene transfer, and the history of life===
The ancestry of living organisms has traditionally been reconstructed from morphology, but is increasingly supplemented with phylogenetics - the reconstruction of phylogenies by the comparison of genetic (DNA) sequence.
"Sequence comparisons suggest recent [[horizontal gene transfer|horizontal transfer]] of many [[gene]]s among diverse [[species]] including across the boundaries of [[Phylogenetics|phylogenetic]] 'domains'. Thus determining the phylogenetic history of a species can not be done conclusively by determining evolutionary trees for single genes." <ref>Oklahoma State - [http://opbs.okstate.edu/~melcher/MG/MGW3/MG334.html Horizontal Gene Transfer]</ref>
Biologist Gogarten suggests "the original metaphor of a tree no longer fits the data from recent genome research", therefore "biologists [should] use the metaphor of a mosaic to describe the different histories combined in individual genomes and use [the] metaphor of a net to visualize the rich exchange and cooperative effects of HGT among microbes." <ref>[http://www.esalenctr.org/display/confpage.cfm?confid=10&pageid=105&pgtype=1 esalenctr.org]</ref>
==References==
{{reflist}}
==External links==
* [http://news.bbc.co.uk/1/hi/sci/tech/944790.stm BBCNews: 27 September, 2000, When slime is not so thick] Citat: "...It means that some of the lowliest creatures in the plant and animal kingdoms, such as slime and amoeba, may not be as primitive as once thought...."
** [http://www.spaceref.com/news/viewpr.html?pid=4742 SpaceRef.com, July 29, 1997: Scientists Discover Methane Ice Worms On Gulf Of Mexico Sea Floor]
*** [http://www.science.psu.edu/iceworms/iceworms.html The Eberly College of Science: Methane Ice Worms discovered on Gulf of Mexico Sea Floor] download Publication quality photos
** [http://www.sb-roscoff.fr/Ecophy/PDF/00-Fisher-NatWis.pdf Artikel, 2000: Methane Ice Worms: Hesiocaeca methanicola. Colonizing Fossil Fuel Reserves]
** [http://www.spaceref.com/news/viewnews.html?id=339 SpaceRef.com, May 04, 2001: Redefining "Life as We Know it"] ''Hesiocaeca methanicola'' In 1997, Charles Fisher, professor of biology at Penn State, discovered this remarkable creature living on mounds of methane ice under half a mile of ocean on the floor of the Gulf of Mexico.
* [http://news.bbc.co.uk/1/hi/sci/tech/2585235.stm BBCNews, 18 December, 2002, 'Space bugs' grown in lab] Citat: "...''Bacillus simplex'' and ''Staphylococcus pasteuri''...''Engyodontium album''...The strains cultured by Dr Wainwright seemed to be resistant to the effects of UV - one quality required for survival in space...."
* [http://news.bbc.co.uk/1/hi/sci/tech/3003946.stm BBCNews, 19 June, 2003, Ancient organism challenges cell evolution] Citat: "..."It appears that this organelle has been conserved in evolution from prokaryotes to eukaryotes, since it is present in both,"..."
* [http://www.anselm.edu/homepage/jpitocch/genbios/bi04syllabsu03.html Interactive Syllabus for General Biology - BI 04, Saint Anselm College, Summer 2003]
* [http://www.personal.psu.edu/users/j/s/jsf165/Bio110.html Jacob Feldman: Stramenopila]
* [http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Root NCBI Taxonomy entry: root] (rich)
* [http://www.anselm.edu/homepage/jpitocch/genbios/surveybi04.html Saint Anselm College: Survey of representatives of the major Kingdoms] Citat: "...Number of [[kingdom (biology)|kingdom]]s has not been resolved...Bacteria present a problem with their diversity...[[Protista]] present a problem with their diversity...",
* [http://www.species2000.org/ Species 2000 Indexing the world's known species]. Species 2000 has the objective of enumerating all known species of plants, animals, fungi and microbes on Earth as the baseline dataset for studies of global biodiversity. It will also provide a simple access point enabling users to link from here to other data systems for all groups of organisms, using direct species-links.
* [http://www.abc.net.au/science/news/enviro/EnviroRepublish_828525.htm The largest organism in the world may be a fungus carpeting nearly 10 square kilometers of an Oregon forest, and may be as old as 10500 years.]
* [http://tolweb.org/tree/phylogeny.html The Tree of Life].
*[http://www.scribd.com/doc/1016/Life-from-birth-to-death/ Frequent questions from kids about life and their answers]
{{Composition}}
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[[Category:Organisms| ]]
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[[it:Organismo vivente]]
[[he:אורגניזם]]
[[jv:Organisme]]
[[kn:ಸಾವಯವ]]
[[lv:Organisms]]
[[lb:Liewewiesen]]
[[lt:Organizmas]]
[[jbo:jmive]]
[[hu:Élőlény]]
[[mk:Организам]]
[[mg:Zavamanan'aina]]
[[nl:Organisme]]
[[ja:生物]]
[[no:Organisme]]
[[nn:Organisme]]
[[oc:Organisme vivent]]
[[uz:Organizm]]
[[pl:Organizm]]
[[pt:Organismo]]
[[ro:Organism]]
[[qu:Kawsaq]]
[[ru:Организм]]
[[scn:Organismu]]
[[simple:Organism]]
[[sl:Organizem]]
[[sr:Организам]]
[[su:Organisme]]
[[fi:Eliö]]
[[sv:Organism]]
[[ta:உயிரினம்]]
[[te:జీవి]]
[[th:สิ่งมีชีวิต]]
[[vi:Sinh vật]]
[[tr:Organizma]]
[[uk:Організм]]
[[yi:ארגאניסם]]
[[zh-yue:生物]]
[[zh:生物]]