Molecular evidence and relationships

Comparing homologous DNA or protein sequences helps estimate evolutionary relatedness. With suitable comparisons, fewer differences generally support a more recent common ancestor. DNA–DNA hybridisation compares how well strands from different sources pair; greater complementarity can increase hybrid stability under comparable conditions. Ribosomal RNA gene sequences are especially useful for comparisons involving prokaryotes.

A phylogenetic tree represents branching relationships. Relatedness depends on the most recent shared branch point, not how close names are printed on the page. Rotating branches at a node does not change ancestry. A molecular-clock calculation requires a stated rate and a clear definition of whether that rate applies per lineage or to total pairwise divergence. Clock estimates depend on assumptions; rates can differ among genes and lineages.

Watch out: Use the most recent common ancestor in the branching pattern, not printed distance.