lineages

A lineage is a sequence of organisms or populations connected by descent from a common ancestor. In biology, it denotes a line of descent through time and is used to study evolutionary relationships, population history, and taxonomy.

Lineages are inferred from data such as morphology, genetics, and fossil records. Phylogenetic trees depict lineages as branches that diverge when lineages split, and they may persist across taxonomic ranks even as species change.

In humans, lineages are studied through maternal and paternal lines using mitochondrial DNA and Y-chromosome markers, and through autosomal DNA to infer family history. This yields haplogroups and family lineages, which can illuminate migrations and demographic events.

In medicine, lineage describes subpopulations of cells in diseases such as cancer. Cancer lineages reflect clonal evolution where cell lineages accumulate mutations and diverge, influencing tumor behavior and treatment responses.

Lineage tracing uses genetic markers, somatic mutations, retroelements, or cell barcoding to reconstruct ancestry or developmental histories. Methods include sequencing, single-cell analysis, and comparative genomics, alongside historical and fossil evidence in paleontology.

Lineage concepts illuminate how organisms and populations are related, how traits and diseases spread, and how diversification occurs over time.