  We use a path integral representation to solve the Eigen and Crow-Kimura
molecular evolution models for the case of multiple fitness peaks with
arbitrary fitness and degradation functions. In the general case, we find that
the solution to these molecular evolution models can be written as the optimum
of a fitness function, with constraints enforced by Lagrange multipliers and
with a term accounting for the entropy of the spreading population in sequence
space. The results for the Eigen model are applied to consider virus or cancer
proliferation under the control of drugs or the immune system.
