Lineage (evolution)

An evolutionary lineage is composed of species, taxa, or individuals that are related by descent from a common ancestor. Lineages are subsets of the evolutionary tree of life. The concept of a lineage is grounded in the evolutionary science of cladistics, and in contemporary science is often determined by the techniques of molecular systematics. A lineage can be distinguished from a mere collection of species by the fact that it contains only and all individuals that share a common ancestor.

The concept of an evolutionary lineage is very similar to the concept of familial lineages in genealogy.

Phylogenetic representation of lineages

File:PhylogeneticTree.jpg

Fig. 1: A rooted tree for rRNA genes

Lineages are typically visualized as subsets of a phylogenetic tree. For example, the tree in Figure 1 shows the separation of life into three ancient lineages: bacteria, archaea, and eukaryotes. Phylogenetic trees are typically created from DNA or protein sequence data. Sequences from different individuals are collected and their similarity is quantified. Mathematical procedures are used to cluster individuals by similarity.

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 Figure 1, the entire lineage of animals has been collapsed to a single "leaf" in 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.

The "lineage" definition of human races

Many contemporary biological definitions of race conceptualize races as evolutionary lineages within the human species. An example of this concept is represented in Figure 2.

Fig. 2: An example of the lineage concept of human races in the context of higher levels of categorization.