Chromosomal Adam

Human genealogical tree of chromosome Y.

According to human Y-chromosomal population genetics, the chromosomal Adam or Y-chromosomal Adam would have been an African man (homologue of mitochondrial Eve) who in evolution human would correspond to the most recent human male common ancestor who possessed the Y chromosome from which all "Y chromosomes" of the current human population are descended.

Therefore, the Y-chromosomal Adam would correspond to a single male ancestor from whom the DNA of the Y chromosome of the entire current population of Homo sapiens (human beings) would converge.

Various estimates of the age of Y-chromosomal Adam have been made, ranging from 60,000 years to 140,000 years. In 2012, haplogroup A00, so far the most divergent and longest-lived, was discovered, thus extended the estimated age of our common ancestor to approximately 340,000 years. However, a comparison between the oldest human haplogroups with the Neanderthal Y-chromosome haplogroup, allows an estimate of an approximate age of 275,000 years for chromosomal Adam. < i>(see: Human Y Chromosome Haplogroups)

Nomenclature

Y-chromosomal Adam is named after the Biblical character Adam recounted in the book of Genesis (in the Bible). This has led to some misunderstanding among the general public. A common opinion is to believe that this Adam would have been the only man living at his time. However, others believe that men before Adam who also belonged to that time, probably also would have had descendants until today. However, it was only the Y-chromosomal Adam who produced a "complete" line of male children to this day; and he is the ancestor from which the entire current population converges.

Also referred to as Y-ACMR (Y-MRCA), which stands for Y-chromosome most recent common ancestor.

Origin

The Y-chromosomal Adam would be the male from whom all the Y chromosomes descend, which determine the male sex.

A biological study at Stanford University of 93 human genetic polymorphisms found on this chromosome, in 1,000 individuals from 21 regions of the world, estimated that a male ancestor or group of ancestors common to all living humans lived in Africa a few years ago. 40,000 to 50,000 years ago, which is consistent with a 1996 study. As of 2003, an age of 60,000 years was estimated, and it was held that the common male ancestor was much later than the common ancestor, for reasons that are unknown and it was considered that the appearance of the Y-chromosomal Adam would be related to the Theory of the Toba catastrophe.

However, studies generally do not include the complete Y chromosome genome of all tested individuals, so it was expected that more in-depth studies would find older mutations. Thus, an Italian geneticist team found in isolated populations from West Africa, North Africa, and in Bakola pygmies from Cameroon, the relict lineages A1a and A1b, which increase the age of Adam by at least twice that previously calculated, recently estimated (2011) about 142,000 years old. This same study suggests that the origin of the chromosomal Adam would be somewhere in the central-northwestern region of Africa; however, it is also stated that this assumption is still very tentative because the sampling of African men is still incomplete, as is knowledge about past demographic events. Indeed, the discovery of a very ancient relict lineage in an African-American family in South Carolina would extend the age of chromosomal Adam to 340,000 years.

Current Y-chromosomes with an older origin

In 2013, a DNA sample from the National Geographic Genographic Project was detected, whose analysis of the Y chromosome turned out to belong to an even earlier branching lineage of a Y chromosome (A00 chromosome), from 338,000 years ago; much older than the oldest Homo sapiens known in the fossil record, (approx. 200,000 years). The researchers found that this chromosome was similar to a type of Y chromosome present in low frequency in the Mbo (a small population living in western Cameroon in sub-Saharan Africa). This ancient lineage of the Y chromosome would belong to a hominid before us, surely some Homo heidelbergensis. It is postulated that this chromosome would be present in some modern humans as a result of an introgression process produced in Africa between a "modern Homo sapiens" with an "archaic Homo sapiens".

Comparison between Y-chromosomal Adam and mitochondrial Eve

Just as Y-chromosomes are inherited paternally, mitochondria are inherited maternally. Therefore it is valid to apply the same principles with these. The closest common maternal ancestor has been nicknamed Mitochondrial Eve.

However, it is very important to clarify that, according to what current knowledge is capable of explaining, scientific Adam and Eve would not have lived at the same time or in the same region within Africa. On the contrary, based on genetic diversity, it is estimated that while the existence of chromosomal Adam would have taken place in West-Central Africa, Eve would have lived in South-East Africa.

In addition, a research team from Stanford University sequenced the Y chromosomes of 69 men from around the world and discovered nearly 9,000 hitherto unknown DNA sequence variations. They used these variations to create a more reliable molecular clock and found that Adam lived between 120,000 and 156,000 years ago. A comparative analysis of mitochondrial DNA sequences from the same men suggested that Eve lived between 99,000 and 148,000 years ago. This indicates that Chromosomal Adam existed before Mitochondrial Eve.

Descendants

The chromosomal Adam phylogenetic tree is organized into groups of haplotypes (haplogroups) as follows: