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Encyclopedia > Last universal ancestor

Last universal ancestor (LUA), the hypothetical latest living organism from which all currently living organisms descend. As such, it is the most recent common ancestor of the set of all currently living organisms. Also LCA (last common ancestor) or LUCA (last universal common ancestor). It is estimated to have lived some 3.5 billion years ago. In biology and ecology, an organism (in Greek organon = instrument) is a complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... The most recent common ancestor (MRCA) of any set of organisms is the most recent individual which is an ancestor of all of them. ... To help compare orders of magnitude of different times this page lists times between 1017 seconds and 1018 seconds (3200 million years and 32 000 million years) See also times of other orders of magnitude. ...

Contents


Misconceptions

The LUCA is not hypothesised as:

  1. the first living organism ever.
  2. the most primitive possible living organism.
  3. being alone.

The hypothesis

Construction of cladograms, based upon genetic distance between all living cells, shows that there was a very early split between the Archaeobacteria that are highly resistant to environmental extremes of great salinity, high temperature or high acidity, and the remainder of life. This has led some to suggest that LUCA evolved in areas like the deep ocean vents, where such extremes prevail today. This cladogram shows the relationship among various insect groups. ... Genetic distance is a measure of the disimilarity of genetic material between different species or individuals of the same species. ... Archaeobacteria, Archaebacteria or Archaea is the name given to a certain class of halo-thermo-acido-philic bacteria, who, on the basis of studies of genetic distance are furtherest removed from all other living things. ... A black smoker in the Atlantic Ocean Black smokers are a type of hydrothermal vent found on the ocean floor. ...


All its contemporaries would have since become extinct with only the LUCA's genetic heritage living on to this day. Carl Woese proposed that our pre-LUCA genetic heritage derives from a community of organisms, rather than an individual.[1] In biology and ecology, extinction is the ceasing of existence of a species or group of taxa. ... Carl Richard Woese (born July 15, 1928) is an American microbiologist famous for defining the Archaea (a new domain or kingdom of life) in 1976 by phylogenetic analysis of 16S ribosomal RNA, a technique pioneered by Woese and which is now standard practice. ...


Horizontal gene transfer

Horizontal gene transfer is a potential confounding factor in inferring phylogenetic trees based on the sequence of one gene. For example, given two distantly related bacteria that have exchanged a gene, a phylogenetic tree including those species will show them to be closely related because that gene is the same, even though most other genes have substantially diverged. For this reason, it is often ideal to use other information to infer robust phylogenies, such as the presence or absence of genes, or, more commonly, to include as wide a range of genes for phylogenetic analysis as possible. Horizontal gene transfer (HGT), also Lateral gene transfer (LGT) is any process in which an organism transfers genetic material (i. ... This article contains information that has not been verified and thus might not be reliable. ... It has been suggested that Evolutionary tree be merged into this article or section. ... In mathematics, a sequence is a list of objects (or events) arranged in a linear fashion, such that the order of the members is well defined and significant. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... It has been suggested that Evolutionary tree be merged into this article or section. ...


For example, the most common gene to be used for constructing phylogenetic relationships in prokaryotes is the 16s rRNA gene, since its sequences tend to be conserved among members with close phylogenetic distances, but variable enough that differences can be measured. However, in recent years it has also been argued that 16s rRNA genes can also be horizontally transferred. Although this may be infrequent, validity of 16s rRNA-constructed phylogenetic trees must be reevaluated. Domain Archaea - Archaebacteria Bacteria - Eubacteria Prokaryotes (from Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos, pl. ...


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." [2]


"Using single genes as phylogenetic markers, it is difficult to trace organismal phylogeny in the presence of HGT [horizontal gene transfer]. Combining the simple coalescence model of cladogenesis with rare HGT [horizontal gene transfer] events suggest there was no single last common ancestor that contained all of the genes ancestral to those shared among the three domains of life. Each contemporary molecule has its own history and traces back to an individual molecule cenancestor. However, these molecular ancestors were likely to be present in different organisms at different times." [3] This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ... Coalescence is the process by which two or more droplets (or bubbles) merge during contact to form a single daughter droplet (or bubble). ... Cladogenesis is an evolutionary splitting event in which each branch and its smaller branches is a clade; an evolutionary mechanism and a process of adaptive evolution that leads to the development of a greater variety of animals or plants. ... Look up life, living in Wiktionary, the free dictionary. ... In chemistry, a molecule is an aggregate of at least two atoms in a definite arrangement held together by special forces. ...


Uprooting the Tree of Life by W. Ford Doolitte (Scientific American, February 2000, pp 72-77) contains a discussion of the Last Universal Common Ancestor, and the problems that arose with respect to that concept when one considers horizontal gene transfer. The article covers a wide area - the endosymbiont hypothesis for eukaryotes, the use of small subunit ribosomal RNA (SSU rRNA) as a measure of evolutionary distances (this was the field Carl Woese worked in when formulating the first modern "tree of life", and his research results with SSU rRNA led him to propose the Archaea as a third domain of life) and other relevant topics. Indeed, it was while examining the new three-domain view of life that horizontal gene transfer arose as a complicating issue: Archaeoglobus fulgidus is cited in the article (p.76) as being an anomaly with respect to a phylogenetic tree based upon the encoding for the enzyme HMGCoA reductase - the organism in question is a definite Archaean, with all the cell lipids and transcription machinery that are expected of an Archaean, but whose HMGCoA genes are actually of bacterial origin. Scientific American is a popular-science magazine, published monthly since August 28, 1845, making it the oldest continuously published magazine in the United States. ... 2000 : January - February - March - April - May - June - July - August - September - October - November - December This is a timeline for events in February, 2000. ... An endosymbiont is any organism that lives within the body or cells of another organism, i. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (IPA: ), also spelled eucaryote, is an organism with a complex cell or cells, in which the genetic material is organized into membrane-bound nucleus/nuclei. ... Ribonucleic acid (RNA) is a nucleic acid polymer consisting of covalently bound nucleotides. ... Carl Richard Woese (born July 15, 1928) is an American microbiologist famous for defining the Archaea (a new domain or kingdom of life) in 1976 by phylogenetic analysis of 16S ribosomal RNA, a technique pioneered by Woese and which is now standard practice. ... Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota The Archaea (; from Greek αρχαία, old ones; singular Archaeum, Archaean, or Archaeon), also called Archaebacteria (), are a major division of living organisms. ... Look up life, living in Wiktionary, the free dictionary. ... A phylogeny (or phylogenesis) is the origin and evolution of a set of organisms, usually of a species. ... Ribbon diagram of the enzyme TIM. TIM is catalytically perfect, meaning its conversion rate is limited, or nearly limited to its substrate diffusion rate. ... HMG-CoA reductase HMG-CoA reductase (or 3-hydroxy-3-methyl-glutaryl-CoA reductase or HMGR) is the first enzyme (EC 1. ...


Again on p.76, the article continues with:

"The weight of evidence still supports the likelihood that mitochondria in eukaryotes derived from alpha-proteobacterial cells and that chloroplasts came from ingested cyanobacteria, but it is no longer safe to assume that those were the only lateral gene transfers that occurred after the first eukaryotes arose. Only in later, multicellular eukaryotes do we know of definite restrictions on horizontal gene exchange, such as the advent of separated (and protected) germ cells."

The article continues with: In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (IPA: ), also spelled eucaryote, is an organism with a complex cell or cells, in which the genetic material is organized into membrane-bound nucleus/nuclei. ... The inside of a chloroplast Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Orders The taxonomy of the Cyanobacteria is currently under revision. ... A germ cell is a kind of cell that is part of the germline, and is involved in the reproduction of organisms. ...

"If there had never been any lateral gene transfer, all these individual gene trees would have the same topology (the same branching order), and the ancestral genes at the root of each tree would have all been present in the last universal common ancestor, a single ancient cell. But extensive transfer means that neither is the case: gene trees will differ (although many will have regions of similar topology) and there would never have been a single cell that could be called the last universal common ancestor.
"As Woese has written, 'the ancestor cannot have been a particular organism, a single organismal lineage. It was communal, a loosely knit, diverse conglomeration of primitive cells that evolved as a unit, and it eventually developed to a stage where it broke into several distinct communities, which in their turn became the three primary lines of descent (bacteria, archaea and eukaryotes)' In other words, early cells, each having relatively few genes, differed in many ways. By swapping genes freely, they shared various of their talents with their contemporaries. Eventually this collection of eclectic and changeable cells coalesced into the three basic domains known today. These domains become recognisable because much (though by no means all) of the gene transfer that occurs these days goes on within domains."

Subgroups Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular: bacterium) are a major group of living organisms. ... Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota The Archaea (; from Greek αρχαία, old ones; singular Archaeum, Archaean, or Archaeon), also called Archaebacteria (), are a major division of living organisms. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Protista A eukaryote (IPA: ), also spelled eucaryote, is an organism with a complex cell or cells, in which the genetic material is organized into membrane-bound nucleus/nuclei. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ...

See also

The origin of life guide (edit)
Science: Origin of life | Evolutionary tree | Common descent | Last universal ancestor
Mythology and religion: Origin belief | Tree of life

 
 

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