2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/147573We present an extension of Eigen's model for quasi-species including the competition among individuals, proposed as the simplest mechanism for the formation of new species in a smooth fitness landscape. We are able to obtain analytically the critical threshold for species formation. The comparison with numerical simulations is very good.6 pages amsmath + psfig + custom ECAL97 style (included) with 3 ps figuresStatistical MechanicsAdaptation and Self-Organizing SystemsBiological PhysicsQuantitative Biologytext