  We exhibit a stochastic discrete time model that has exactly the Eigen model
as its deterministic continuous limit. Such model can be divided into two
phases: reproduction followed by neutral selection. This result suggests that
Eigen model describes the competition among individuals differing for
reproductive capability but equivalent as survivors. We explicitly write down
the Markov matrix of the stochastic model in the two species case and compute
numerically the master sequence concentration for various values of the total
population. Finally we compare our results with those obtained with Eigen model
and with Nowak and Schuster birth and death model.
