In human genetics, the Y-chromosomal Adam (more technically known as the Y-chromosomal most recent common ancestor, shortened to Y-MRCA), is the patrilineal most recent common ancestor (MRCA) from whom all currently living humans are descended. He is the most recent male from whom all living humans are descended through an unbroken line of their male ancestors. The term Y-MRCA reflects the fact that the Y chromosomes of all currently living human 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. As with "Mitochondrial Eve", the title of "Y-chromosomal Adam" is not permanently fixed to a single individual, but can advance over the course of human history as paternal lineages become extinct.
Estimates of the time when Y-MRCA lived have also shifted as modern knowledge of human ancestry changes. For example, in 2013, the discovery of a previously unknown Y-chromosomal haplogroup was announced,
which resulted in a slight adjustment of the estimated age of the human Y-MRCA.
By definition, it is not necessary that the Y-MRCA and the mt-MRCA should have lived at the same time.
While estimates as of 2014 suggested the possibility that the two individuals may well have been roughly contemporaneous, the discovery of the archaic Y-haplogroup has pushed back the estimated age of the Y-MRCA beyond the most likely age of the mt-MRCA. As of 2015, estimates of the age of the Y-MRCA range around 200,000 to 300,000 years ago, roughly consistent with the emergence of anatomically modern humans.
Y-chromosomal data taken from a Neanderthal from El Sidrón, Spain, produced a Y-T-MRCA (time to Y-MRCA) of 588,000 years ago for Neanderthal and Homo sapiens patrilineages, dubbed ante Adam, and 275,000 years ago for Y-MRCA.
Definition
The Y-chromosomal most recent common ancestor is the most recent common ancestor of the Y-chromosomes found in currently living human males.
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. <!--as has sometimes been naively proposed based on naive association with the Genesis narrative (who has even come up with this and why does it have to be debunked in a prominent position of this article?)-->
His other male contemporaries may also have descendants alive today, but not, by definition, through solely patrilineal descent; in other words, none of them have an unbroken male line of descendants (son's son's son's … son) connecting them to currently living people.
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).
Age estimate
Estimates on the age of the Y-MRCA crucially depend on the most archaic known haplogroup extant in contemporary populations. , this is haplogroup A00 (discovered in 2013). Age estimates based on this published during 2014–2015 range between 160,000 and 300,000 years, compatible with the time of emergence and early dispersal of Homo sapiens.
Such estimates were later substantially revised downward, as in Thomson et al. 2000, which proposed an age of about 59,000.
This date suggested that the Y-MRCA lived about 84,000 years after his female counterpart mt-MRCA (the matrilineal most recent common ancestor), who lived 150,000–200,000 years ago.
This date also meant that Y-chromosomal Adam lived at a time very close to, and possibly after, the migration from Africa which is believed to have taken place 50,000–80,000 years ago.
One explanation given for this discrepancy in the time depths of patrilineal vs. matrilineal lineages was that females have a better chance of reproducing than males due to the practice of polygyny. When a male individual has several wives, he has effectively prevented other males in the community from reproducing and passing on their Y chromosomes to subsequent generations. On the other hand, polygyny does not prevent most females in a community from passing on their mitochondrial DNA to subsequent generations. This differential reproductive success of males and females can lead to fewer male lineages relative to female lineages persisting into the future. These fewer male lineages are more sensitive to drift and would most likely coalesce on a more recent common ancestor. This would potentially explain the more recent dates associated with the Y-MRCA.
The "hyper-recent" estimate of significantly below 100 kya was again corrected upward in studies of the early 2010s, which ranged at about 120 kya to 160 kya.
This revision was due to the rearrangement of the backbone of the Y-chromosome phylogeny following the resequencing of Haplogroup A lineages.
In 2013, Francalacci et al. reported the sequencing of male-specific single-nucleotide Y-chromosome polymorphisms (MSY-SNPs) from 1204 Sardinian males, which indicated an estimate of 180,000 to 200,000 years for the common origin of all humans through paternal lineage.
Also in 2013, Poznik et al. reported the Y-MRCA to have lived between 120,000 and 156,000 years ago, based on genome sequencing of 69 men from 9 different populations.
In addition, the same study estimated the age of Mitochondrial Eve to about 99,000 and 148,000 years. As these ranges overlap for a time-range of 28,000 years (148 to 120 kya), the results of this study have been cast in terms of the possibility that "Genetic Adam and Eve may have walked on Earth at the same time" in the popular press.
The announcement by Mendez et al. Y-chromosomal Adam was represented as the root of these two lineages. Haplogroup A and Haplogroup BT represented the lineages of Y-chromosomal Adam himself and of one of his sons, who had a new SNP.
Cruciani et al. 2011, determined that the deepest split in the Y-chromosome tree was found between two previously reported subclades of Haplogroup A, rather than between Haplogroup A and Haplogroup BT. Later, group A00 was found, outside of the previously known tree.
The rearrangement of the Y-chromosome family tree implies that lineages classified as Haplogroup A do not necessarily form a monophyletic clade. Haplogroup A therefore refers to a collection of lineages that do not possess the markers that define Haplogroup BT, though Haplogroup A includes the most distantly related Y chromosomes.
The M91 and P97 mutations distinguish Haplogroup A from Haplogroup BT. Within Haplogroup A chromosomes, the M91 marker consists of a stretch of 8 T nucleobase units. In Haplogroup BT and chimpanzee chromosomes, this marker consists of 9 T nucleobase units. This pattern suggested that the 9T stretch of Haplogroup BT was the ancestral version and that Haplogroup A was formed by the deletion of one nucleobase. Haplogroups A1b and A1a were considered subclades of Haplogroup A as they both possessed the M91 with 8Ts.
Scozzari et al. (2012) agreed with a plausible placement in "the north-western quadrant of the African continent" for the emergence of the A1b haplogroup.
The 2013 report of haplogroup A00 found among the Mbo people of western present-day Cameroon is also compatible with this picture.