Phylogenetic tree

BacteriaArchaeaEucaryotaAquifexThermotogaCytophagaBacteroidesBacteroides-CytophagaPlanctomycesCyanobacteriaProteobacteriaSpirochetesGram-positive bacteriaGreen filantous bacteriaPyrodicticumThermoproteusThermococcus celerMethanococcusMethanobacteriumMethanosarcinaHalophilesEntamoebaeSlime moldAnimalFungusPlantCiliateFlagellateTrichomonadMicrosporidiaDiplomonad
A speculatively rooted tree for rRNA genes, showing the three life domains: bacteria, archaea, and eukaryota. The black trunk at the bottom of the tree links the three branches of living organisms to the last universal common ancestor.
A rooted phylogenetic tree, illustrating how Eukaryota and Archaea are more closely related to each other than to Bacteria (based on Cavalier-Smith's theory of bacterial evolution). Neomura is a clade composed of two life domains, Archaea and Eukaryota.

A phylogenetic tree or evolutionary tree is a branching diagram or "tree" showing the evolutionary relationships among various biological species or other entities—their phylogeny (i/)—based upon similarities and differences in their physical or genetic characteristics. All life on Earth is part of a single phylogenetic tree, indicating common ancestry.

In a rooted phylogenetic tree, each node with descendants represents the inferred most recent common ancestor of those descendants, and the edge lengths in some trees may be interpreted as time estimates. Each node is called a taxonomic unit. Internal nodes are generally called hypothetical taxonomic units, as they cannot be directly observed. Trees are useful in fields of biology such as bioinformatics, systematics, and phylogenetics. Unrooted trees illustrate only the relatedness of the leaf nodes and do not require the ancestral root to be known or inferred.

History

The idea of a "tree of life" arose from ancient notions of a ladder-like progression from lower into higher forms of life (such as in the Great Chain of Being). Early representations of "branching" phylogenetic trees include a "paleontological chart" showing the geological relationships among plants and animals in the book Elementary Geology, by Edward Hitchcock (first edition: 1840).

Charles Darwin (1859) also produced one of the first illustrations and crucially popularized the notion of an evolutionary "tree" in his seminal book The Origin of Species. Over a century later, evolutionary biologists still use tree diagrams to depict evolution because such diagrams effectively convey the concept that speciation occurs through the adaptive and semirandom splitting of lineages. Over time, species classification has become less static and more dynamic.

The term phylogenetic, or phylogeny, derives from the two ancient greek words φῦλον (phûlon), meaning "race, lineage", and γένεσις (génesis), meaning "origin, source".[1][2]

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