In biology, phylogenetics /ˌfləˈnɛtɪks, -lə-/[1][2] (from Greek φυλή/φῦλον (phylé/phylon) "tribe, clan, race", and γενετικός (genetikós) "origin, source, birth")[3] is a part of systematics that addresses the inference of the evolutionary history and relationships among or within groups of organisms (e.g. species, or more inclusive taxa). These relationships are hypothesized by phylogenetic inference methods that evaluate observed heritable traits, such as DNA sequences, protein amino acid sequences, or morphology, often under a specified model of evolution of these traits. The result of such an analysis is a phylogeny (also known as a phylogenetic tree)—a diagrammatic hypothesis of relationships that reflects the evolutionary history of a group of organisms.[4] The tips of a phylogenetic tree can be living taxa or fossils, and represent the 'end', or the present, in an evolutionary lineage. A phylogenetic diagram can be rooted or unrooted. A rooted tree diagram indicates the hypothetical common ancestor, or ancestral lineage, of the tree. An unrooted tree diagram (a network) makes no assumption about the ancestral line, and does not show the origin or "root" of the taxa in question or the direction of inferred evolutionary transformations.[5] In addition to their proper use for inferring phylogenetic patterns among taxa, phylogenetic analyses are often employed to represent relationships among gene copies or individual organisms. Such uses have become central to understanding biodiversity, evolution, ecology, and genomes. In February 2021, scientists reported, for the first time, the sequencing of DNA from animal remains, a mammoth in this instance, over a million years old, the oldest DNA sequenced to date.[6][7]

Taxonomy is the identification, naming and classification of organisms. Classifications are now usually based on phylogenetic data, and many systematists contend that only monophyletic taxa should be recognized as named groups. The degree to which classification depends on inferred evolutionary history differs depending on the school of taxonomy: phenetics ignores phylogenetic speculation altogether, trying to represent the similarity between organisms instead; cladistics (phylogenetic systematics) tries to reflect phylogeny in its classifications by only recognizing groups based on shared, derived characters (synapomorphies); evolutionary taxonomy tries to take into account both the branching pattern and "degree of difference" to find a compromise between them.