concept

Error threshold

Eigen's limit on how much information a replicator can hold: at copying accuracy q per base, sequences longer than about ln(σ)/(1−q) dissolve into noise faster than selection can rebuild them. The consequence is a hard circle for the origin problem — bare chemistry holds only a few dozen nucleotides, while a folded RNA replicase needs 170–200, which is to say it needs exactly the accuracy that only it could provide.