Maximal gene number maintainable by stochastic correction - The second error threshold.

There is still no general solution to Eigen׳s Paradox, the chicken-or-egg problem of the origin of life: neither accurate copying, nor long genomes could have evolved without one another being established beforehand. But an array of small, individually replicating genes might offer a workaround, provided that multilevel selection assists the survival of the ensemble. There are two key difficulties that such a system has to overcome: the non-synchronous replication of genes, and their random assortment into daughter cells (the units of higher-level selection) upon fission. Here we find, using the Stochastic Corrector Model framework, that a large number (τ≥90) of genes can coexist. Furthermore, the system can tolerate about 10% replication rate asymmetry (competition) among the genes. On this basis, we put forward a plausible (and testable!) scenario for how novel genes could have been incorporated into early living systems: a route to complex metabolism.