The presumed shallow time depth of the human Y-chromosome
phylogeny is one of the main arguments of the recent Out-of-
Africa theory. One of the major things I found while working on
my Y-STR series is that point estimates from Y-STR variation are
associated with huge confidence intervals, because of
uncertainty about factors such as generation length, population
history, mutation rates, even if the mutation model behaves
"perfectly" in symmetrical stepwise fashion. Trouble is, the
deeper we go in time, the more uncertain we are about the
behavior of our models. That is why I have generally avoided
providing any age estimates for events prior to the Neolithic.
Nonetheless, it is interesting to see the state of the art in
this area, because claims about the shallow time depth of the
human Y-chromosome phylogeny are always flying around, but, if
you follow the citation labyrinth, you will soon realize that
the whole edifice is erected on sand. Fortunately, I was
recently reminded of a thoughtful post by Tim Janz