In graph theory and computer science, the lowest common ancestor (also called least common ancestor) of two nodes and in a tree or directed acyclic graph is the lowest (i.e. deepest) node that has both and as descendants, where we define each node to be a descendant of itself (so if has a direct connection from , is the lowest common ancestor).

The last universal common ancestor is the hypothesized common ancestral cell from which the three domains of life, the Bacteria, the Archaea, and the Eukarya originated.

In biology and genetic genealogy, the most recent common ancestor, also known as the last common ancestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended.