That was intensely painful. Jeanson is making up facts and fitting other made-up facts to them. It also has nothing to do with mutation rates. You understand that Jeanson’s force-fitting of the Y-chromosome tree to his model means that many human populations diverged from each other after 1500, right? But he doesn’t talk about the simple departure of that part of the data from reality. Further, he claims that it’s universally agreed that the population curve fits what he shows, but he shows a world population of only a few million in 1000 BC, and nobody agrees with that.
Perhaps most importantly, his initial assumption is wrong: the Y-chromosome tree doesn’t track population size. You would get a similar tree even if the population hadn’t changed at all in thousands of years. Jeanson seems completely unaware of coalescence theory, which you should look up.
Urk.