molecular clocks

[Marc Roussel]

In article <9109081355.AA14144 at evolution.genetics.washington.edu>
joe at GENETICS.WASHINGTON.EDU (Joe Felsenstein) writes:
>   The actual formula for probability of fixation of a mutant is (to
>extremely good approximation) given by Kimura's formula:
>
>     Prob(fixation)  =  (1 - exp(-4Nsp))/(1-exp(-4Ns))
>
>with p = 1/(2N) if the mutant is initially present in one copy (s is the
>increase in fitness in the heterozygote carrying the mutant).

     I would like to know more about this equation.  Is it an empirical
law?  If not, what assumptions go into it?  Can anyone provide us with a
reference that discusses and/or derives this law with a minimum of
hocus-pocus?

                                Sincerely,

				Marc R. Roussel
                                mroussel at alchemy.chem.utoronto.ca