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. Thus a lineage is a single branch of the tree. 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 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 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.