Last common ancestor

In biology and genealogy, the most recent common ancestor (MRCA, also last common ancestor LCA, or concestor) of any set of organisms is the most recent individual from which all organisms in a group are directly descended. The term is also used reference to the ancestry of groups of genes (haplotypes) rather than organisms.

The MRCA of a set of individuals can sometimes be determined by referring to an established pedigree. However, in general, it is impossible to identify the exact MRCA of a large set of individuals, but an estimate of the time at which the MRCA lived can often be given. Such time to MRCA (TMRCA) estimates can be given based on DNA test results and established mutation rates as practiced in genetic genealogy, or by reference to a non-genetic, mathematical model or computer simulation.

In organisms using sexual reproduction, the matrilinear MRCA and patrilinear MRCA are the MRCAs of a given population considering only matrilineal and patrilineal descent, respectively. The MRCA of a population by definition cannot be older than either its matrilinear or its patrilinear MRCA. In the case of Homo sapiens, the matrilinear and patrilinear MRCA are also known as "" (mt-MRCA) and "Y-chromosomal Adam" (Y-MRCA) respectively.

The age of the human MRCA is unknown. It is necessarily younger than the age of both Y-MRCA and mt-MRCA, estimated at around 200,000 years, and it may be as recent as some 3,000 years ago.

The Last Universal Common Ancestor (LUCA) is the most recent common ancestor of all current life on Earth, estimated to have lived some 3.5 to 3.8 billion years ago (in the Paleoarchean).

The project of a complete description of the phylogeny of biological species is dubbed the "Tree of Life". This involves time estimates of all known speciation events; for example, the MRCA of all Carnivora (i.e. the MRCA of "cats and dogs") is estimated to have lived of the order of 42 million years ago (Miacidae).

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