  Mendez et al. recently report the identification of a Y chromosome lineage
from an African American that is an outgroup to all other known Y haplotypes,
and report a time to most recent common ancestor, TMRCA, for human Y lineages
that is substantially longer than any previous estimate. The identification of
a novel Y haplotype is always exciting, and this haplotype, in particular, is
unique in its basal position on the Y haplotype tree. However, at 338 (237-581)
thousand years ago, kya, the extremely ancient TMRCA reported by Mendez et al.
is inconsistent with the known human fossil record (which estimate the age of
anatomically modern humans at 195 +- 5 kya), with estimates from mtDNA (176.6
+- 11.3 kya, and 204.9 (116.8-295.7) kya) and with population genetic theory.
The inflated TMRCA can quite easily be attributed to the extremely low Y
chromosome mutation rate used by the authors.
