There’s a new paper in AJHG (open access), The Divergence of Neandertal and Modern Human Y Chromosomes. From the discussion:
The fact that the Neandertal Y-chromosome lineage we describe has never been observed in modern humans suggests that the lineage is most likely extinct. Although the Neandertal Y chromosome (and mtDNA) might have simply drifted out of the modern human gene pool…it is also possible that genetic incompatibilities contributed to their loss. In comparing the Neandertal lineage to those of modern humans, we identified four coding differences with predicted functional impacts, three missense and one nonsense….
For obvious reasons the media has found the argument of functional differences compelling. E.g., Anne Gibbons in Science, Modern human females and male Neandertals had trouble making babies. Here’s why. That’s fine. But I think it is important to note that for many people the loss of ancient Y chromosomes is actually a pretty strong null model. Basically, Y and mtDNA are tree phylogenetic trees (no reticulation), and as you traverse up the tree you note that there is consistent gene loss as surviving lineages coalesce together. Additionally, the rate of extinction will be higher because of higher drift in uniparental lineages (Y and mtDNA effective population sizes are constrained to one sex).
As far back the mid-2000s John Hawks was arguing that lack of high diverged mtDNA and Y lineages, which would suggest archaic admixture, was not evidence for lack of admixture, because of the high likelihood of extinction. In other words, lack of evidence in this case tells us far less than evidence itself.
Comments are closed.