Editing Most recent common ancestor (section)

== Time to MRCA estimates ==
Different types of MRCAs are estimated to have lived at different times in the past. These ''time to MRCA'' (''TMRCA'') estimates are also computed differently depending on the type of MRCA being considered. Patrilineal and matrilineal MRCAs (Mitochondrial Eve and Y-chromosomal Adam) are traced by single gene markers, thus their TMRCA are computed based on DNA test results and established mutation rates as practiced in genetic genealogy. The time to the genealogical MRCA (most recent common ancestor by any line of descent) of all living humans cannot be traced genetically because the DNA of the great majority of ancestors is completely lost after a few hundred years. It is therefore computed based on non-genetic, mathematical models and computer simulations.

Since Mitochondrial Eve and Y-chromosomal Adam are traced by single genes via a single ancestral parent line, the time to these genetic MRCAs will necessarily be greater than that for the genealogical MRCA. This is because single genes will coalesce more slowly than tracing of conventional human genealogy via both parents. The latter considers only individual humans, without taking into account whether any gene from the computed MRCA actually survives in every single person in the current population.<ref name=chang_1999>{{cite journal |doi= 10.1239/aap/1029955256|last1=Chang |first1=Joseph T. |title=Recent common ancestors of all present-day individuals |journal=Advances in Applied Probability |volume=31 |issue=4 |pages=1002–26, discussion and author's reply, 1027–38 |year=1999 |url= http://www.stat.yale.edu/~jtc5/papers/Ancestors.pdf |access-date=2008-01-29 |last2=Donnelly |first2=Peter |last3=Wiuf |first3=Carsten |last4=Hein |first4=Jotun |last5=Slatkin |first5=Montgomery |last6=Ewens |first6=W. J. |last7=Kingman |first7=J. F. C.| citeseerx=10.1.1.408.8868 |s2cid=1090239 }}</ref>

=== TMRCA via genetic markers ===
Mitochondrial DNA can be used to trace the ancestry of a set of populations. In this case, populations are defined by the accumulation of mutations on the mtDNA, and special trees are created for the mutations and the order in which they occurred in each population. The tree is formed through the testing of a large number of individuals all over the world for the presence or lack of a certain set of mutations. Once this is done it is possible to determine how many mutations separate one population from another. The number of mutations, together with estimated mutation rate of the mtDNA in the regions tested, allows scientists to determine the approximate time to MRCA (''TMRCA'') which indicates time passed since the populations last shared the same set of mutations or belonged to the same [[haplogroup]].

In the case of Y-Chromosomal DNA, TMRCA is arrived at in a different way. [[Human Y-chromosome DNA haplogroup|Y-DNA haplogroups]] are defined by [[single-nucleotide polymorphism]] in various regions of the Y-DNA. The time to MRCA within a haplogroup is defined by the accumulation of mutations in [[Short tandem repeat|STR]] sequences of the Y-Chromosome of that haplogroup only. Y-DNA network analysis of [[Y-STR]] [[haplotypes]] showing a non-star cluster indicates Y-STR variability due to multiple founding individuals. Analysis yielding a star cluster can be regarded as representing a population descended from a single ancestor. In this case the variability of the [[Y-STR]] sequence, also called the [[Microsatellite (genetics)|microsatellite]] variation, can be regarded as a measure of the time passed since the ancestor founded this particular population. The [[Descent from Genghis Khan|descendants of Genghis Khan]] or one of his ancestors represents a famous star cluster that can be dated back to the time of Genghis Khan.<ref>{{cite journal |last1=Zerjal |first1=Tatiana |last2=Xue |first2=Yali |last3=Bertorelle |first3=Giorgio |last4=Wells |first4=R. Spencer |last5=Bao |first5=Weidong |last6=Zhu |first6=Suling |last7=Qamar |first7=Raheel |last8=Ayub |first8=Qasim |last9=Mohyuddin |first9=Aisha |last10=Fu |first10=Songbin |last11=Li |first11=Pu |last12=Yuldasheva |first12=Nadira |last13=Ruzibakiev |first13=Ruslan |last14=Xu |first14=Jiujin |last15=Shu |first15=Qunfang |last16=Du |first16=Ruofu |last17=Yang |first17=Huanming |last18=Hurles |first18=Matthew E. |last19=Robinson |first19=Elizabeth |last20=Gerelsaikhan |first20=Tudevdagva |last21=Dashnyam |first21=Bumbein |last22=Mehdi |first22=S. Qasim |last23=Tyler-Smith |first23=Chris |title=The Genetic Legacy of the Mongols |journal=The American Journal of Human Genetics |date=March 2003 |volume=72 |issue=3 |pages=717–721 |doi=10.1086/367774|pmid=12592608 |pmc=1180246 }}</ref>

TMRCA calculations are considered critical evidence when attempting to determine migration dates of various populations as they spread around the world. For example, if a mutation is deemed to have occurred 30,000 years ago, then this mutation should be found amongst all populations that diverged after this date. If archeological evidence indicates cultural spread and formation of regionally isolated populations then this must be reflected in the isolation of subsequent genetic mutations in this region. If genetic divergence and regional divergence coincide it can be concluded that the observed divergence is due to migration as evidenced by the archaeological record. However, if the date of genetic divergence occurs at a different time than the archaeological record, then scientists will have to look at alternate archaeological evidence to explain the genetic divergence. The issue is best illustrated in the debate surrounding the [[demic diffusion]] versus [[cultural diffusion]] during the [[Neolithic Europe|European Neolithic]].<ref>{{cite journal |last1=Morelli |first1=Laura |last2=Contu |first2=Daniela |last3=Santoni |first3=Federico |last4=Whalen |first4=Michael B. |last5=Francalacci |first5=Paolo |last6=Cucca |first6=Francesco |title=A Comparison of Y-Chromosome Variation in Sardinia and Anatolia Is More Consistent with Cultural Rather than Demic Diffusion of Agriculture |journal=PLOS ONE |date=29 April 2010 |volume=5 |issue=4 |pages=e10419 |doi=10.1371/journal.pone.0010419 |pmid=20454687 |pmc=2861676 |doi-access=free|bibcode=2010PLoSO...510419M }}</ref>

=== TMRCA of all living humans ===
The age of the MRCA of all living humans is unknown. It is necessarily younger than the age of either the matrilinear or the patrilinear MRCA, both of which have an estimated age of between roughly 100,000 and 200,000 years ago.<ref>{{cite journal |last1=Poznik |first1=G. David |last2=Henn |first2=Brenna M. |last3=Yee |first3=Muh-Ching |last4=Sliwerska |first4=Elzbieta |last5=Euskirchen |first5=Ghia M. |last6=Lin |first6=Alice A. |last7=Snyder |first7=Michael |last8=Quintana-Murci |first8=Lluis |last9=Kidd |first9=Jeffrey M. |last10=Underhill |first10=Peter A. |last11=Bustamante |first11=Carlos D. |title=Sequencing Y Chromosomes Resolves Discrepancy in Time to Common Ancestor of Males Versus Females |journal=Science |date=2 August 2013 |volume=341 |issue=6145 |pages=562–565 |doi=10.1126/science.1237619 |pmid=23908239 |pmc=4032117 |bibcode=2013Sci...341..562P}}</ref>

A study by mathematicians Joseph T. Chang, Douglas Rohde and Steve Olson used a theoretical model to calculate that the MRCA may have lived remarkably recently, possibly as recently as 2,000 years ago. It concludes that the MRCA of all living humans probably lived in East Asia, which would have given them key access to extremely isolated populations in Australia and the Americas. Possible locations for the MRCA include places such as the Chuckchi and Kamchatka Peninsulas that are close to Alaska, places such as Indonesia and Malaysia that are close to Australia or a place such as Taiwan or Japan that is more intermediate to Australia and the Americas. European colonization of the Americas and Australia was found by Chang to be too recent to have had a substantial impact on the age of the MRCA. In fact, if the Americas and Australia had never been discovered by Europeans, the MRCA would only be about 2.3% further back in the past than it is.<ref>{{Cite news |last=Crenson |first=Matt |date=July 2006 |title=Roots of Human Family Tree Are Shallow |url=https://www.washingtonpost.com/wp-dyn/content/article/2006/07/01/AR2006070100463.html |access-date=2024-06-30 |newspaper=The Washington Post}}</ref><ref>{{Cite web |last=Rohde |first=Douglas L. T. |date=November 11, 2003 |title=On the Common Ancestors of All Living Humans |url=https://tedlab.mit.edu/~dr/Papers/Rohde-MRCA-two.pdf |url-status=dead |archive-url=https://web.archive.org/web/20181230184319/http://tedlab.mit.edu/~dr/Papers/Rohde-MRCA-two.pdf |archive-date=2018-12-30 |access-date=2018-05-01 |website=tedlab.mit.edu}}</ref><ref>{{cite web |date=September 30, 2004 |title='Most Recent Common Ancestor' of All Living Humans Surprisingly Recent |url=https://www.sciencedaily.com/releases/2004/09/040930122428.htm |access-date=2024-06-30 |website=Science Daily}}</ref>

Note that the age of the MRCA of a population does not correspond to a [[population bottleneck]], let alone a "first couple". It rather reflects the presence of a single individual with high reproductive success in the past, whose genetic contribution has become pervasive throughout the population over time. It is also incorrect to assume that the MRCA passed all, or indeed any, genetic information to every living person. Through [[sexual reproduction]], an ancestor passes half of his or her genes to each descendant in the next generation; in the absence of [[pedigree collapse]], after just 32 generations the contribution of a single ancestor would be on the order of 2<sup>−32</sup>, a number proportional to less than a single basepair within the [[human genome]].<ref>{{cite journal |last1=Zhaxybayeva |first1=Olga |last2=Lapierre |first2=Pascal |last3=Gogarten |first3=J.Peter |title=Genome mosaicism and organismal lineages |journal=[[Trends in Genetics]] |date=May 2004 |volume=20 |issue=5 |pages=254–260 |doi=10.1016/j.tig.2004.03.009 |pmid=15109780 |quote=The Ship of Theseus paradox […] is frequently invoked to illustrate this point […]. Even moderate levels of gene transfer will make it impossible to reconstruct the genomes of early ancestors; … |citeseerx=10.1.1.530.7843}}</ref>