Dating Y chromosomal "Adam"
How old is our species? Where did we come from? How did our ancestors migrate around the world and who did they encounter? These questions are very difficult to study without access to the genetic material of our ancestors. Thus far the most ancient humans sequenced were no older than 50,000 years old whereas our species is estimated to be at least four times older. One way to address such questions is by studying mutations along the mitochondrial and Y chromosomes.
Y chromosomal "Adam" is the name of the most ancient Y chromosome ever found. In 2013, Mendez and colleagues reported the identification of a Y chromosome haplotype (the A00 lineage) that lies at the basal position of the Y chromosome phylogenetic tree. Incorporating this haplotype, the authors estimated the time to the most recent common ancestor (TMRCA) for the Y tree to be 338 000 years ago (95% CI:237 000-581 000). Such an extraordinarily early estimate contradicts all previous estimates in the literature and is over a 100,000 years older than the earliest fossils of anatomically modern humans.
We demonstrate that the TMRCA estimate was reached through inadequate statistical and analytical methods, each of which contributed to its inflation. We show that the authors ignored previously inferred Y-specific rates of substitution, incorrectly derived the Y-specific substitution rate from autosomal mutation rates, and compared unequal lengths of the novel Y chromosome with the previously recognized basal lineage. Our analysis indicates that the A00 lineage was derived from all the other lineages 208 300 (95% CI:163,900-260,200) years ago.
- Elhaik E, Tatarinova TV, Klyosov AA, Graur D: The ‘extremely ancient’ chromosome that isn’t: a forensic bioinformatic investigation of Albert Perry’s X-degenerate portion of the Y chromosome. Eur J Hum Genet 2014, 22(9):1111-1116.
- Elhaik E, Tatarinova TV, Klyosov AA, Graur D: An extended reply to Mendez et al.: The 'extremely ancient' chromosome that still isn't. arXiv preprint arXiv:14103972 2014.
- Elhaik E, Tatarinova TV, Klyosov AA, Graur D: Reply to Mendez et al: the ‘extremely ancient’chromosome that still isn’t. Eur J Hum Genet 2015.
- Morozova I, Flegontov P, Mikheyev AS, Bruskin S, Asgharian H, Ponomarenko P, Klyuchnikov V, ArunKumar G, Prokhortchouk E, Gankin Y et al: Toward high-resolution population genomics using archaeological samples. DNA Res 2016, 23(4):295-310.