An answer from Brian Charlesworth:
As promised, here is my best attempt to give what the good professor, most kindly and courteously, provided. I’ll not paste in his words since he did not invite me to and I would hate to repay him with stealing his creation. The spread of a neutral mutation to fixation in a population is not the number of generations equal to the size of the population but four times that. Similarly the prevalence of a neutral mutation and the rate at which that mutation enters the population will reach equilibrium and let you calculate (knowing prevalence and mutation rate) a number that is four times the population size.
What I learned was that if you know the rate at which some neutral mutation enters a population and know the prevalence of the population you can calculate and “effective population size.” What I think it said was that a single population will vanish on average in a number of generations commensurate with the population size. Mutation rates are about 10-8 per site per generation and level of variability about .001 per site suggesting 25, 000 being our calculated effective population size.
Splitting or nearly splitting a population increases the calculated population size. (This surprises me.) However the local populations have a smaller calculated size, which is what I would have expected. He goes on to say that 85% of total variability is in restricted areas. Hmm. Calculating what happened in the past suggest that it was most complex. He recommends the book:
Late Pleistocene climate change and the global expansion of anatomically modern humans. Author: Anders, Lia et al. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA , 2012, Vol.109(40), p.16089-16094
Clearly that restriction of population sizes we have been dealing with is not a game changer at this time.
Again my warmest thanks go to him.
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