Before revision:  We model frequency-dependent selection pressure with a general polynomial drift vanishing at the boundary. An appropriate decomposition of the drift allows us to construct a series of Moran-type models that converge under suitable conditions to the solution of the associated stochastic differential equation  .
After revision:  We model frequency-dependent selection. A decomposition of the drift allows us to construct a series of Moran-type models that converge under suitable conditions to the solution of the associated stochastic differential equation .