2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/17570We discuss a simple model of co-evolution. In order to emphasise the effect of interaction between individuals the entire population is subjected to the same physical environment. Species are emergent structures and extinction, origination and diversity are entirely a consequence of co-evolutionary interaction between individuals. For comparison we consider both asexual and sexually reproducing populations. We also study competition between asexual and sexual reproduction in a mixed population. In either case the system evolves through periods of hectic reorganisation separated by periods of coherent stable coexistence.11 pages, 11 figures, submitted to Journal of Theoretical BiologyStatistical MechanicsQuantitative Biologytext