Quasispecies Model

The quasispecies model is a mathematical framework for evolution in systems with high mutation rates, developed by Manfred Eigen and Peter Schuster in the 1970s to describe the first replicators on Earth. It extends the replicator dynamics of evolutionary dynamics by incorporating mutation as a systematic operator rather than a perturbation. The model's central prediction is the error threshold: if the mutation rate per base exceeds the reciprocal of the sequence length, the fittest sequence cannot maintain its dominance and the population collapses into a disordered cloud of mutants — an error catastrophe. This framework has been applied to viral evolution (explaining why RNA viruses mutate so rapidly yet remain functional), to the origins of life (where prebiotic replicators must have operated near the threshold), and increasingly to cultural and computational systems where fidelity of transmission competes with innovation. The quasispecies concept challenges the classical view of evolution as a hill-climbing process by showing that at high mutation rates, the unit of selection is not an individual sequence but a correlated ensemble.