Before revision:  In the preceding manuscript, we analyzed dimensionless free energy changes, \Delta \psi_N (= \Delta G_N /  k_B T_s ), due to single nucleotide mutations, for which the total interaction \psi_N of a sequence was estimated from a multiple sequence alignment . Based on this analyis, we study the equilibrium state of protein stability in a monoclonal approximation, in which protein evolution proceeds with single amino acid substitutions fixed at a time in a population. The ensemble of proteins attains the equilibrium, \psi_N= \psi_N ^{eq, where the average of \Delta \psi}  _{ N } over fixed mutants is equal to zero.
After revision:  In the preceding manuscript, we analyzed dimensionless free energy changes, \Delta \psi_N (= \Delta G_N / k_B T_s ), due to single nucleotide mutations, for which the total interaction \psi_N of a sequence was estimated from a multiple sequence alignment . Based on , where the average of \Delta \psi} _{ N } over fixed mutants is equal to zero.