Editing Lineage (evolution) (section)

== Phylogenetic representation of lineages ==
{{unreferenced section|date=November 2016}}
[[image:Phylogenetic_tree.svg|thumb|upright=1.4|A rooted tree of life into three ancient monophyletic lineages: [[bacteria]], [[archaea]], and [[eukaryotes]] based on [[rRNA]] genes]]

Lineages are typically visualized as subsets of a [[phylogenetic tree]]. A lineage is a single line of descent or linear chain within the tree, while a [[clade]] is a (usually branched) [[monophyletic]] group, containing a single ancestor and all its descendants.<ref>{{Cite web |title=Blood Cell Lineage {{!}} SEER Training |url=https://training.seer.cancer.gov/leukemia/anatomy/lineage.html |access-date=2024-07-26 |website=training.seer.cancer.gov}}</ref> [[Phylogenetic]] trees are typically created from [[DNA]], RNA or [[protein]] sequence data. Apart from this, morphological differences and similarities have been, and still are used to create phylogenetic trees. Sequences from different individuals are collected and their similarity is quantified. Mathematical procedures are used to [[data clustering|cluster]] individuals by similarity.<ref name=":0">{{Cite book |title=Encyclopedia of Evolutionary Biology |publisher=Academic Press |year=2016 |isbn=9780128004265 |editor-last=Kliman |editor-first=R. M. |chapter=Phylogenetic Tree}}</ref>

Members of a species are considered to evolve as a single unit (or lineage) when they repeatedly share the same genes. The nodes would represent a split in lineage due to a breaking of genetic connections: when a single lineage is divided into two subsets, with the individuals not exchanging genes, they will accumulate differences in genes. If they do not fuse back again, it will create a new distinct descendant clade.<ref name=":0" /> 

Just as a map is a scaled approximation of true [[geography]], a phylogenetic tree is an approximation of the true complete [[evolutionary]] relationships. For example, in a full tree of life, the entire clade of animals can be collapsed to a single branch of the tree. However, this is merely a limitation of rendering space. In theory, a true and complete tree for all living organisms or for any [[DNA]] sequence could be generated.<ref name=":0" />

Nevertheless, phylogenies can sometimes appear in a non-treelike form. Branches on the [[Tree of life (biology)|tree of life]] may grow together, a phenomenon called [[Reticulation (single-access key)|reticulation]], which occurs due to different biological processes. Another process, [[introgression]], occurs when hybrids between distinct lineages transfer novel genetic material through subsequent crossing. In other cases, [[hybrid speciation]] takes place when lineages hybridize to form a new, distinct lineage. Horizontal gene transfer, involving the introgression of very few genes, usually appears as a treelike population history with some genes having a discordant history. Thus, the tree-like representation would be proper as long as introgression and hybrid speciation are rare or limited to closely related tips (of lineages). In some cases, evolutionary relantionships should be depicted better in the form of a network.<ref name=":0" />