The discovery of the A00 lineage changes the phylogenetic context of the male lineages. The TMRCA estimate presented (338,000 years old) is older than previous values for the entire Y-tree (usually 60-140,000 years old) and even exceeds the date of the oldest fossils of modern humans. This means that the male lineage has survived a very long period outside the clades known so far. Since the A00 lineage was not detected in hunter-gatherer groups (e.g., Bushmen or Pygmies), but in the Bantu (Mbo) people, the authors emphasize the high variability of the random genealogical process. They point out that conclusions about human ancestry from only a single locus (like the Y chromosome) can be misleading. The extremely old age and low abundance of the A00 line suggest to the authors the need to modify evolutionary models. They suggest accounting for archaic population structure or even introgression (mixing) from archaic hominin populations into the ancestors of Homo sapiens. In other words, they suggest that the ancestors of modern humans may have had a complex, long-lasting structure (perhaps with numerous subgroups) and that some very old Y-lineages may have originated from archaic, extinct human groups. These conclusions underscore the need for caution in interpreting the phylogenetic position of Y-ChR tree branches, and point to the potential for further research - for example, in the search for other distinct Y chromosome lineages in sub-Saharan Africa. Summary: The discovery of the chrY A00 line marks the oldest known "root" of the phylogenetic tree of male lineages, estimated at ~338,000 years ago. This lineage is found in African American and in a small percentage of Cameroonian (Mbo) people. The rare presence and age of A00 suggest that the evolution of the human species was complex - the authors postulate an archaic introgression or deep structure of the former population, necessitating a revision of previous models of human origins. All observations point to unambiguous conclusions: the phylogeny of humans based on a single gene (the Y chromosome) may show a much longer history than thought, and lines such as A00 represent the oldest surviving relics of ancient gene pool variation. The study describes the discovery of a new male ("patrilineal") chrY line, designated A00, in the DNA of an African American. This line carries the ancestral state (primary alleles) for all previously known SNPs defining the oldest part of the phylogenetic tree of the Y chromosome. Sequencing of ~240 kb of this line was carried out, resulting in an estimate of the time to the nearest common ancestor (TMRCA) of the entire Y chromosome tree as 338,000 years ago (95% confidence interval 237-581,000 years). This is significantly higher than previous TMRCA estimates for mtDNA (~140-240 thousand years) and than the age of the oldest known Homo sapiens fossils. The discovered A00 lineage is very rare - aside from African American, identical Y-STR profiles have only been found in a single group of people from western Cameroon (the Mbo people). In a sample of 174 individuals from the Mbo people, 11 A00-type chromosomes were found (~6.3%). Microsatellite mutation analysis showed that the A00 chromosome of the African American differs by 11 mutations from the closest A00 chromosome from the Mbo, and the maximum difference between any two Mbo chromosomes is 9 mutations. Phylogenetic models suggest that the common ancestor of these A00 chromosomes lived between about 2.6 and 73,000 years ago (ML≈17,000 years). Based on this, the authors estimate the time of separation of A00 chromosomes from the AfAm and Mbo lineages to be ~0.6-2.7 thousand years ago (assuming typical Y-STR mutation rates). These results suggest a recent ancestral commonality between the A00 lineage carrier among African Americans and its representatives in Cameroon.