NOTE 18H: There is a subtlety here, when effective population size N_e differs from actual size N. The actual number of mutations generated at n loci is 2nNμ, but the probability that each one is fixed is 2s(N_e/N). Hence, the number of mutations that fix is 4snN_eμ. Thus, we can use the effective poulation size throughout the calculation: The actual number cancels.