Most recent common ancestor

In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA), of a set of organisms is the most recent individual from which all the organisms of the set are descended. The term is also used in 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 most recent common ancestor (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 matrilineal MRCA and patrilineal 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 matrilineal or its patrilineal MRCA. In the case of Homo sapiens, the matrilineal and patrilineal MRCA are also known as "Mitochondrial Eve" (mt-MRCA) and "Y-chromosomal Adam" (Y-MRCA) respectively.

The age of the human MRCA is unknown. It is no greater than the age of either the Y-MRCA or the mt-MRCA, estimated at around 200,000 years.

Unlike in pedigrees of individual humans or domesticated lineages where historical parentage is known, in the inference of relationships among species or higher groups of taxa (systematics or phylogenetics), ancestors are not directly observable or recognizable. They are inferences based on patterns of relationship among taxa inferred in a phylogenetic analysis of extant organisms and/or fossils.^[1]

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).^{[2][3][note 1]}

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