In
biology, an organism () is any
living system that functions as an individual entity.
All organisms are composed of cells (
cell theory
In biology, cell theory is a scientific theory first formulated in the mid-nineteenth century, that living organisms are made up of cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pre ...
).
Organisms are classified by
taxonomy into groups such as
multicellular animals,
plants, and
fungi; or
unicellular microorganisms such as
protists,
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
, and
archaea. All types of organisms are capable of
reproduction,
growth and development,
maintenance
Maintenance may refer to:
Biological science
* Maintenance of an organism
* Maintenance respiration
Non-technical maintenance
* Alimony, also called ''maintenance'' in British English
* Champerty and maintenance, two related legal doct ...
, and some degree of response to
stimuli.
Beetles,
squids,
tetrapods,
mushrooms, and
vascular plants are examples of multicellular organisms that
differentiate specialized
tissues and
organs during
development
Development or developing may refer to:
Arts
*Development hell, when a project is stuck in development
*Filmmaking, development phase, including finance and budgeting
*Development (music), the process thematic material is reshaped
* Photograph ...
.
A
unicellular organism may be either a
prokaryote or a
eukaryote. Prokaryotes are represented by two separate
domains –
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
and
archaea. Eukaryotic organisms are characterized by the presence of a membrane-bound
cell nucleus and contain additional membrane-bound compartments called
organelles (such as
mitochondria in animals and plants and
plastids in plants and
algae, all generally considered to be derived from
endosymbiotic
An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.
(The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...
bacteria).
Fungi, animals and plants are examples of
kingdoms of organisms within the eukaryotes.
Estimates on the number of Earth's current
species range from 2 million to 1 trillion,
of which over 1.7 million have been documented. More than 99% of all species, amounting to over five billion species,
that ever lived are estimated to be
extinct.
In 2016, a set of 355
genes from the
last universal common ancestor
The last universal common ancestor (LUCA) is the most recent population from which all organisms now living on Earth share common descent—the most recent common ancestor of all current life on Earth. This includes all cellular organisms; th ...
(LUCA) of all organisms from Earth was identified.
Etymology
The term "organism" (from
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
ὀργανισμός, ''organismos'', from ὄργανον, ''organon'', i.e. "instrument, implement, tool, organ of sense or apprehension")
first appeared in the English language in 1703 and took on its current definition by 1834 (
Oxford English Dictionary). It is directly related to the term "organization". There is a long tradition of defining organisms as self-organizing beings, going back at least to
Immanuel Kant's 1790 ''
Critique of Judgment''.
Definitions
An organism may be defined as an assembly of
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
s functioning as a more or less stable whole that exhibits the
properties of life. Dictionary definitions can be broad, using phrases such as "any living structure, such as a plant, animal, fungus or bacterium, capable of growth and reproduction".
Many definitions exclude
viruses and possible man-made
non-organic life forms, as viruses are dependent on the biochemical machinery of a host cell for reproduction.
A
superorganism
A superorganism or supraorganism is a group of synergetically interacting organisms of the same species. A community of synergetically interacting organisms of different species is called a holobiont.
Concept
The term superorganism is used m ...
is an organism consisting of many individuals working together as a single functional or
social unit
The term "level of analysis" is used in the social sciences to point to the location, size, or scale of a research target.
"Level of analysis" is distinct from the term " unit of observation" in that the former refers to a more or less integrated ...
.
There has been controversy about the best way to define the organism and indeed about whether or not such a definition is necessary. Several contributions are responses to the suggestion that the category of "organism" may well not be adequate in biology.
Viruses
Viruses are not typically considered to be organisms because they are incapable of autonomous
reproduction, growth or
metabolism. Although some organisms are also incapable of independent survival and live as obligatory intracellular
parasites
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...
, they are capable of independent metabolism and procreation. Although viruses have a few
enzymes and molecules characteristic of living organisms, they have no metabolism of their own; they cannot synthesize and organize the organic compounds from which they are formed. Naturally, this rules out autonomous reproduction: they can only be passively replicated by the machinery of the
host cell. In this sense, they are similar to inanimate matter.
While viruses sustain no independent metabolism and thus are usually not classified as organisms, they do have their own
genes, and they do
evolve by mechanisms similar to the evolutionary mechanisms of organisms. Thus, an argument that viruses should be classed as living organisms is their ability to undergo evolution and replicate through self-assembly. However, some scientists argue that viruses neither evolve nor self-reproduce. Instead, viruses are evolved by their host cells, meaning that there was co-evolution of viruses and host cells. If host cells did not exist, viral evolution would be impossible. This is not true for cells. If viruses did not exist, the direction of cellular evolution could be different, but cells would nevertheless be able to evolve. As for reproduction, viruses rely on hosts' machinery to replicate.
The discovery of viruses with genes coding for energy metabolism and protein synthesis fuelled the debate about whether viruses are living organisms. The presence of these genes suggested that viruses were once able to metabolize. However, it was found later that the genes coding for energy and protein metabolism have a cellular origin. Most likely, these genes were acquired through
horizontal gene transfer
Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). H ...
from viral hosts.
Chemistry
Organisms are complex chemical systems, organized in ways that promote reproduction and some measure of sustainability or survival. The same laws that govern non-living chemistry govern
the chemical processes of life. It is generally the phenomena of entire organisms that determine their fitness to an environment and therefore the survival 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 compounds that, through interaction and 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
An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Wo ...
s produce usable energy (in the form of organic compounds) using light from the sun or inorganic compounds while
heterotrophs take in organic compounds from the environment.
The primary
chemical element in these compounds is
carbon. The
chemical properties
A chemical property is any of a material's properties that becomes evident during, or after, a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity.William L. Masterton, Cecile N. Hurley, ...
of this element such as its great affinity for bonding with other small atoms, including other carbon atoms, and its small size making it capable of forming multiple bonds, make it ideal as the basis of organic life. It is able to form small three-atom compounds (such as
carbon dioxide), as well as large chains of many thousands of atoms that can store data (
nucleic acids), hold cells together, and transmit information (protein).
Macromolecules
Compounds that make up organisms may be divided into
macromolecules and other, smaller molecules. The four groups of macromolecule are
nucleic acids,
proteins,
carbohydrates and
lipids. Nucleic acids (specifically deoxyribonucleic acid, or DNA) store genetic data as a sequence of
nucleotides. The particular sequence of the four different types of nucleotides (
adenine,
cytosine,
guanine, and
thymine) dictate many characteristics that constitute the organism. The sequence is divided up into
codons, 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 that, due to the chemical properties of the amino acids it is made from,
folds in a particular manner and so performs a particular function.
These protein functions have been recognized:
#
Enzymes, which catalyze the reactions of metabolism
# Structural proteins, such as
tubulin
Tubulin in molecular biology can refer either to the tubulin protein superfamily of globular proteins, or one of the member proteins of that superfamily. α- and β-tubulins polymerize into microtubules, a major component of the eukaryotic cytoske ...
, 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
Dendrotoxins are a class of presynaptic neurotoxins produced by mamba snakes ('' Dendroaspis'') that block particular subtypes of voltage-gated potassium channels in neurons, thereby enhancing the release of acetylcholine at neuromuscular junctio ...
s of snakes), to proteins that include unusual amino acids like
canavanine
A bilayer of
phospholipids makes up the
membrane
A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...
of cells that constitutes a barrier, containing everything within a cell and preventing compounds from freely passing into, and out of, the cell. Due to the selective permeability of the phospholipid membrane, only specific compounds can pass through it.
Structure
All organisms consist of structural units called
cells; 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 a
tissue, and in animals these occur as four basic types, namely
epithelium,
nervous tissue,
muscle tissue
Muscle tissue (or muscular tissue) is soft tissue that makes up the different types of muscles in most animals, and give the ability of muscles to contract. Muscle tissue is formed during embryonic development, in a process known as myogenesis. ...
, and
connective tissue. Several types of tissue work together in the form of an
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
An organ system is a biological system consisting of a group of organs that work together to perform one or more functions. Each organ has a specialized role in a plant or animal body, and is made up of distinct tissues.
Plants
Plants have ...
such as the
reproductive system, and
digestive system. Many multicellular organisms consist of several organ systems, which coordinate to allow for life.
Cell
The
cell theory
In biology, cell theory is a scientific theory first formulated in the mid-nineteenth century, that living organisms are made up of cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pre ...
, first developed in 1839 by
Schleiden and
Schwann, states that all organisms are composed of one or more cells; all cells come from preexisting cells, and cells contain the
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 multicellular organisms. Prokaryotic cells lack a
nuclear membrane
The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer membranes that in eukaryotic cells surround the nucleus, which encloses the genetic material.
The nuclear envelope consists of two lipid bilayer membra ...
so
DNA is unbound within the cell; eukaryotic cells have nuclear membranes.
All cells, whether prokaryotic or eukaryotic, have a
membrane
A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...
, which envelops the cell, separates its interior from its environment, regulates what moves in and out, and maintains the
electric potential of the cell. Inside the membrane, a
salty
cytoplasm takes up most of the cell volume. All cells possess DNA, the hereditary material of
genes, and
RNA, containing the information necessary to
build various
proteins such as
enzymes, the cell's primary machinery. There are also other kinds of
biomolecules in cells.
All cells share several similar characteristics of:
* Reproduction by
cell division (
binary fission
Binary may refer to:
Science and technology Mathematics
* Binary number, a representation of numbers using only two digits (0 and 1)
* Binary function, a function that takes two arguments
* Binary operation, a mathematical operation that ta ...
,
mitosis or
meiosis).
* Use of enzymes and other proteins
coded by DNA genes and made via
messenger RNA intermediates and
ribosomes.
* Metabolism, including taking in raw materials, building cell components, converting energy,
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
s and releasing
by-products. 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 pathways.
* Response to external and internal
stimuli such as changes in temperature,
pH or nutrient levels.
* Cell contents are contained within a
cell surface membrane that contains proteins and a
lipid bilayer
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many vir ...
.
Evolutionary history
Last universal common ancestor
The last universal common ancestor (LUCA) is the most recent organism from which all organisms now living on Earth
descend.
Thus it is the
most recent common ancestor
In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The ...
of all current life on Earth. The LUCA is estimated to have lived some
3.5 to 3.8 billion years ago (sometime in the
Paleoarchean
The Paleoarchean (), also spelled Palaeoarchaean (formerly known as early Archean), is a geologic era within the Archaean Eon. The name derives from Greek "Palaios" ''ancient''. It spans the period of time . The era is defined chronometrically a ...
era). The earliest evidence for
life on Earth is
graphite found to be
biogenic in 3.7 billion-year-old
metasedimentary rocks
In geology, metasedimentary rock is a type of metamorphic rock. Such a rock was first formed through the deposition and solidification of sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and e ...
discovered in
Western Greenland and
microbial mat
A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea, or bacteria alone. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in deserts ...
fossils found in 3.48 billion-year-old
sandstone discovered in
Western Australia
Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
.
Although more than 99 percent of all species that ever lived on the planet are estimated to be extinct,
it is likely that more than a billion species of life exist on Earth currently, with the highest estimates and projections reaching one trillion species.
Information about the early development of life includes input from many different fields, including
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.
All organisms 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 that do not fly.
There is strong evidence from genetics that all organisms have a common ancestor. For example, every living cell makes use of
nucleic acids as its genetic material, and uses the same twenty
amino acids as the building blocks for
proteins. All organisms use the same
genetic code
The genetic code is the set of rules used by living cells to translate information encoded within genetic material ( DNA or RNA sequences of nucleotide triplets, or codons) into proteins. Translation is accomplished by the ribosome, which links ...
(with some extremely rare and minor deviations) to
translate
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transl ...
nucleic acid sequences into proteins. The universality of these traits strongly suggests common ancestry, because the selection of many of these traits seems arbitrary.
Horizontal gene transfer
Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). H ...
makes it more difficult to study the last universal ancestor. However, the universal use of the same genetic code, same nucleotides, and same amino acids makes the existence of such an ancestor overwhelmingly likely.
The first organisms were possibly anaerobic and thermophilic chemolithoautotrophis that evolved within inorganic compartments at geothermal environments.
Phylogeny
Location of the root
The most commonly accepted location of the root of the
tree of life
The tree of life is a fundamental archetype in many of the world's mythological, religious, and philosophical traditions. It is closely related to the concept of the sacred tree.Giovino, Mariana (2007). ''The Assyrian Sacred Tree: A Hist ...
is between a
monophyletic
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
domain
Domain may refer to:
Mathematics
*Domain of a function, the set of input values for which the (total) function is defined
**Domain of definition of a partial function
**Natural domain of a partial function
**Domain of holomorphy of a function
* Do ...
Bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
and a
clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
formed by
Archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
and
Eukaryota of what is referred to as the "traditional tree of life" based on several molecular studies. A very small minority of studies have concluded differently, namely that the root is in the domain Bacteria, either in the phylum
Bacillota
The Bacillota (synonym Firmicutes) are a phylum of bacteria, most of which have gram-positive cell wall structure. The renaming of phyla such as Firmicutes in 2021 remains controversial among microbiologists, many of whom continue to use the earl ...
or that the phylum
Chloroflexota
The Chloroflexota are a phylum of bacteria containing isolates with a diversity of phenotypes, including members that are aerobic thermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for phot ...
is basal to a clade with Archaea and Eukaryotes and the rest of Bacteria as proposed by
Thomas Cavalier-Smith
Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021), was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford.
His research has led to discov ...
.
Research published in 2016, by
William F. Martin, by genetically analyzing 6.1 million protein-coding genes from sequenced prokaryotic genomes of various phylogenetic trees, identified 355 protein clusters from amongst 286,514 protein clusters that were probably common to the LUCA. The results "depict LUCA as
anaerobic
Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to:
* Anaerobic adhesive, a bonding a ...
, CO
2-fixing, H
2-dependent with a
Wood–Ljungdahl pathway (the reductive
acetyl-coenzyme A
Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for ...
pathway), N
2-fixing and thermophilic. LUCA's biochemistry was replete with FeS clusters and radical reaction mechanisms. Its cofactors reveal dependence upon
transition metals
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that ca ...
,
flavins
Flavins (from Latin ''flavus'', "yellow") are organic compounds, like their base, pteridine. They are formed by the tricyclic heterocycle isoalloxazine. The biochemical source is the vitamin riboflavin. The flavin moiety is often attached with ...
,
S-adenosyl methionine
''S''-Adenosyl methionine (SAM), also known under the commercial names of SAMe, SAM-e, or AdoMet, is a common cosubstrate involved in methyl group transfers, transsulfuration, and aminopropylation. Although these anabolic reactions occur throug ...
,
coenzyme A,
ferredoxin,
molybdopterin
Molybdopterins are a class of cofactors found in most molybdenum-containing and all tungsten-containing enzymes. Synonyms for molybdopterin are: MPT and pyranopterin-dithiolate. The nomenclature for this biomolecule can be confusing: Molybdopteri ...
,
corrin
Corrin is a heterocyclic compound. It is the parent macrocycle related to the substituted derivative that is found in vitamin B12. Its name reflects that it is the "core" of vitamin B12 (cobalamins).Nelson, D. L.; Cox, M. M. "Lehninger, Princi ...
s and
selenium
Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
. Its genetic code required
nucleoside
Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group. A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar (ribose or 2'-deoxyribose) whereas a nucleoti ...
modifications and S-adenosylmethionine-dependent
methylations." The results depict
methanogenic
clostria as a basal clade in the 355 lineages examined, and suggest that the LUCA inhabited an anaerobic
hydrothermal vent setting in a geochemically active environment rich in H
2, CO
2, and iron.
[ However, the identification of these genes as being present in LUCA was criticized, suggesting that many of the proteins assumed to be present in LUCA represent later horizontal gene transfers between archaea and bacteria.
]
Reproduction
Sexual reproduction
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
is widespread among current eukaryotes, and was likely present in the last common ancestor. This is suggested by the finding of a core set of genes for meiosis in the descendants of lineages that diverged early from the eukaryotic evolutionary tree. and Malik et al. It is further supported by evidence that eukaryotes previously regarded as "ancient asexuals", such as ''Amoeba
An amoeba (; less commonly spelled ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and retracting pseudop ...
'', were likely sexual in the past, and that most present day asexual amoeboid lineages likely arose recently and independently.
In prokaryotes, natural bacterial transformation involves the transfer of DNA from one bacterium to another and integration of the donor DNA into the recipient chromosome by recombination. Natural bacterial transformation is considered to be a primitive sexual process and occurs in both bacteria and archaea, although it has been studied mainly in bacteria. Transformation is clearly a bacterial adaptation and not an accidental occurrence, because it depends on numerous gene products that specifically interact with each other to enter a state of natural competence
In microbiology, genetics, cell biology, and molecular biology, competence is the ability of a cell to alter its genetics by taking up extracellular ("naked") DNA from its environment in the process called transformation. Competence may be diff ...
to perform this complex process. Transformation is a common mode of DNA transfer among prokaryotes.
Horizontal gene transfer
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 transfer of many genes among diverse species including across the boundaries of phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
"domains". Thus determining the phylogenetic history of a species can not be done conclusively by determining evolutionary trees for single genes.
Biologist Peter 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."
Future of life (cloning and synthetic organisms)
Modern biotechnology is challenging traditional concepts of organisms and species. Cloning
Cloning is the process of producing individual organisms with identical or virtually identical DNA, either by natural or artificial means. In nature, some organisms produce clones through asexual reproduction. In the field of biotechnology, c ...
is the process of creating a new multicellular organism, genetically identical to another, with the potential of creating entirely new species of organisms. Cloning is the subject of much ethical debate.
In 2008, the J. Craig Venter Institute assembled a synthetic bacterial genome
Bacterial genomes are generally smaller and less variant in size among species when compared with genomes of eukaryotes. Bacterial genomes can range in size anywhere from about 130 kbp to over 14 Mbp. A study that included, but was not limited to ...
, ''Mycoplasma genitalium
''Mycoplasma genitalium'' (''MG'', commonly known as Mgen) is a sexually transmitted, small and pathogenic bacterium that lives on the mucous epithelial cells of the urinary and genital tracts in humans. Medical reports published in 2007 and 2 ...
'', by using recombination in yeast of 25 overlapping DNA fragments in a single step. The use of yeast recombination greatly simplifies the assembly of large DNA molecules from both synthetic and natural fragments. Other companies, such as Synthetic Genomics, have already been formed to take advantage of the many commercial uses of custom designed genomes.
See also
* Earliest known life forms
The earliest known life forms on Earth are believed to be fossilized microorganisms found in hydrothermal vent precipitates, considered to be about 3.42 billion years old. The earliest time for the origin of life on Earth is at least 3.77 bill ...
References
Further reading
*
*
*
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*
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*
*
External links
*
* 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.
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