Phylogenetic tree

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A phylogenetic tree based on rRNA genes,^{[citation needed]} showing the three life domains: bacteria, archaea, and eukaryota. The black branch at the bottom of the phylogenetic tree connects the three branches of living organisms to the last universal common ancestor. In the absence of an outgroup, the root is speculative.

A highly resolved, automatically generated tree of life, based on completely sequenced genomes.^[1][2]

A phylogenetic tree (also phylogeny or evolutionary tree ^[3]) is a branching diagram or a tree showing the evolutionary relationships among various biological species or other entities 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,^[4] 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.