The master equation of an ecosystem in evolution on a static fitness landscape can be written as a sum over all possible phylogenetic generations of individuals. Such a time trajectory represents alternating phases of selection (the fitness landscape) and mutation (during reproduction). This approach permits to restrict the sum to the most probable paths. For medium and small time scales, a smooth landscape and long-range mutations it is shown that the equilibrium distribution is of Boltzmann type, with the fitness as an energy and mutations as temperature.