Molecular clock errors

Jim Cummins cummins at
Thu Dec 10 23:08:11 EST 1998

Discrepanacies can arise in estimating speciation and common ancestors
using mtDNA and Y chromosome polymorphisms.  I think this is because both
are subject to sexual selection and hence mutations do not accumulate
randomly.  In the case of the Y in humans, for example, there are multiple
copies of genes that affect spermatogenesis. Deletions or mutations will
result in sterility or subfertility.  Hence estimates of convergence times
for Y chromosomes are typically much less than for mtDNA (60,000 years
versus 250,000 or so).  I have some good data now on actual reproductive
success in historical human populations for both men and women, and it's
very highly skewed with a minority of individuals contributing the
majority of progeny in the next generation.  Is anyone working on models
of Y or mtDNA evolution that take differential fertility into account?

Jim Cummins <cummins at

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