  Describing the evolution of a population of genomes evolving in a complex
fitness landscape is generally very hard. We here introduce an approximate
Gaussian closure scheme to characterize analytically the statistics of a
genomic population in the so-called Quasi--Linkage Equilibrium (QLE) regime,
applicable to generic values of the rates of mutation or recombination and
fitness functions. The Gaussian approximation is illustrated on a short-range
fitness landscape with two far away and competing maxima. It unveils the
existence of a phase transition from a broad to a polarized distribution of
genomes as the strength of epistatic couplings is increased, characterized by
slow coarsening dynamics of competing allele domains. Results of the closure
scheme are corroborated by numerical simulations.
