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In human genetics, Y-chromosomal most recent common ancestor (Y-MRCA; informally also known as Y-chromosomal Adam) refers to the most recent common ancestor (MRCA) from whom all currently living people are descended patrilineally. The term Y-MRCA reflects the fact that the Y chromosomes of all currently living males are directly derived from the Y chromosome of this remote ancestor. The analogous concept of the matrilineal most recent common ancestor is known as "Mitochondrial Eve" (mt-MRCA, named for the matrilineal transmission of mtDNA), the most recent woman from whom all living humans are descended matrilineally. By the nature of the concept of most recent common ancestors, these estimates can only represent a ''terminus ante quem'' ("limit before which"), until the genome of the entire population has been examined (in this case, the genome of all living humans). In 2013, the discovery of a previously unknown Y-chromosomal haplogroup was announced,〔 (primary source)〕 which resulted in a slight adjustment of the estimated age of the human Y-MRCA.〔 ('Y-Chromosomal Adam Lived 208,300 Years Ago, Says New Study' ), Sci-News.com, 23 January 2014.〕 Current estimates of the Y-MRCA range around 200,000 to 300,000 years ago, consistent with the emergence of anatomically modern humans and overlapping with age estimates for the mt-MRCA (matrilinear MRCA).〔Karmin et al., "A recent bottleneck of Y chromosome diversity coincides with a global change in culture", ''Genome Research'' (2015), doi:10.1101/gr.186684.114. "we date the Y-chromosomal most recent common ancestor (MRCA) in Africa at 254 (95% CI 192–307) kya and detect a cluster of major non-African founder haplogroups in a narrow time interval at 47–52 kya, consistent with a rapid initial colonization model of Eurasia and Oceania after the out-of-Africa bottleneck. In contrast to demographic reconstructions based on mtDNA, we infer a second strong bottleneck in Y-chromosome lineages dating to the last 10 ky. We hypothesize that this bottleneck is caused by cultural changes affecting variance of reproductive success among males." 〕 By definition, it is not necessary that the Y-MRCA and the mt-MRCA should have lived at the same time, even though current () estimates suggest the possibility that the two individuals may well have been roughly contemporaneous (albeit with uncertainties ranging in the tens of thousands of years). ==Definition== The existence of a Y-MRCA for any given human population is a consequence of the fact that every human being has a biological father, and that every human male inherits his Y chromosome from his biological father. We assume quite reasonably that every man inherited his Y chromosome from some common ancestor (say, the first creature to have a Y chromosome). So there had to be a male who was the last one from whom all men inherit their Y chromosome. (It is not a logical necessity that that male was a ''Homo sapiens'' however.) Although the informal name "Y-chromosomal Adam" is a reference to the biblical Adam, this should not be misconstrued as implying that the bearer of the chromosome was the only human male alive during his time. His other male contemporaries also have descendants alive today, but not, by definition, through solely patrilineal descent. Due to the definition via the "currently living" population, the identity of a MRCA, and by extension of the human Y-MRCA, is time-dependent (it depends on the moment in time intended by the term "currently"). The MRCA of a population may move forward in time as archaic lineages within the population go extinct: once a lineage has died out, it is irretrievably lost. This mechanism can thus only shift the title of Y-MRCA forward in time. Such an event could be due to the total extinction of several basal haplogroups.〔 The same holds for the concepts of matrilineal and patrilineal MRCAs: it follows from the definition of Y-MRCA that he had at least two sons who both have unbroken lineages that have survived to the present day. If the lineages of all but one of those sons die out, then the title of Y-MRCA shifts forward from the remaining son through his patrilineal descendants, until the first descendant is reached who had at least two sons who both have living, patrilineal descendants. The title of Y-MRCA is not permanently fixed to a single individual, and the Y-MRCA for any given population would himself have been part of a population which had its own, more remote, Y-MRCA. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Y-chromosomal Adam」の詳細全文を読む スポンサード リンク
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