The origin of synergistic symbiosis

A dominant theme in the history of life has been the evolutionary innovations of cooperative symbioses] the _rst genomes near the origin of life \ integrated prokaryotic cells \ the complex symbiotic communities that evolved into modern eukaryotic cells \ lichens \ mycorrhizae \ and so on [ In this paper \ a model of cooperative symbiosis that shows a threshold condition for the evolution of cooperation is analyzed [ The threshold is not easily passed \ but cooperative evolution proceeds rapidly once a symbiosis overcomes the threshold [ In the model presented here \ each species has genetic variability for a symbiotic trait [ The trait imposes a reproductive cost on its bearer but enhances the reproduction of its partner species [ For example \ in the origin of genetic systems \ the trait may cause biochemical synergism for the rate of replication of primitive RNA strands as in Eigen and Schuster|s hypercycle model [ Models of growth synergism \ which are most appropriate for the evolution of genetic systems and for mutualisms such as lichens \ with the strategic and psychological applications of the Prisoner|s Dilemma model[ 7 0884 Academic Press Limite