Editing Most recent common ancestor (section)

{{short description|Most recent individual from which all organisms in a group are directly descended}}
{{About||lowest common ancestors in graph theory and computer science|Lowest common ancestor|methyl-coenzyme M reductase (MCR) and subunits in methanogenesis|Coenzyme-B sulfoethylthiotransferase}}
{{genetic genealogy}}
A '''most recent common ancestor''' ('''MRCA'''), also known as a '''last common ancestor''' ('''LCA'''), is the most recent individual from which all organisms of a set are inferred to have [[Common descent|descended]]. The most recent common ancestor of a higher taxon is generally assumed to have been a [[species]].  The term is also used in reference to the ancestry of groups of [[gene]]s ([[haplotype]]s) rather than organisms.

The ancestry of a set of individuals can sometimes be determined by referring to an established [[pedigree chart|pedigree]], although this may refer only to patrilineal or matrilineal lines for sexually-reproducing organisms with two parents, four grandparents, etc. 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 rate]]s 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 200,000 years.

Unlike in pedigrees of individual humans or domesticated lineages where historical parentage is known for some number of generations into the past, ancestors are not directly observable or recognizable in the inference of relationships among species or higher groups of [[taxa]] ([[systematics]] or [[phylogenetics]]). Ancestors are inferences based on patterns of relationship among taxa inferred in a [[phylogenetic analysis]] of extant organisms and/or [[fossils]].<ref>{{cite book |last1=Brower |first1=Andrew V. Z. |last2=Schuh |first2=Randall T. |title=Biological systematics: principles and applications |date=2021 |publisher=Cornell University Press |location=Ithaca, New York |isbn=9781501752797 |edition=Third}}</ref>

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]]).<ref>{{cite journal |last1=Doolittle |first1=W. Ford |title=Uprooting the Tree of Life |journal=Scientific American |date=February 2000 |volume=282 |issue=2 |pages=90–95 |doi=10.1038/scientificamerican0200-90 |pmid=10710791 |bibcode=2000SciAm.282b..90D }}</ref><ref>{{cite journal |last1=Glansdorff |first1=Nicolas |last2=Xu |first2=Ying |last3=Labedan |first3=Bernard |title=The Last Universal Common Ancestor: emergence, constitution and genetic legacy of an elusive forerunner |journal=Biology Direct |date=December 2008 |volume=3 |issue=1 |page=29 |doi=10.1186/1745-6150-3-29 |pmid=18613974 |pmc=2478661 |doi-access=free }}</ref>{{efn|group=note|The composition of the LUCA is not directly accessible as a fossil, but can be studied by [[phylogenetic bracketing|comparing the genomes of its descendants]], organisms living today. By this means, a 2016 study identified a set of 355 [[gene]]s inferred to have been present in the LUCA.<ref>{{cite news |last=Wade |first=Nicholas |author-link=Nicholas Wade |title=Meet Luca, the Ancestor of All Living Things|url= https://www.nytimes.com/2016/07/26/science/last-universal-ancestor.html |date=25 July 2016 |work=[[New York Times]] |access-date=25 July 2016 }}</ref>}}