On origins of life, it is widely thought that life systems like modern living organisms emerged through a process of increasing complexity from simple replicators such as RNA and protein. It is unclear how this process occurred, but it is far distant from now, so evolutionary experiments are useful for investigating it.
　To date, we have conducted a long-term evolutionary experiment simulating primitive replicator systems. We enclosed RNA molecules encoding an RNA replicase together with cell-free translation system derived from E. coli within water-in-oil emulsions, enabling RNA to replicate via translation and evolve. In this experiment, we observed the emergence of short parasitic RNAs that had lost the replicase gene from host RNAs that retained it. Competition between host and parasitic RNAs led to spontaneous RNA diversification and the formation of replication networks.
　However, even using the same experimental system, different dilution and agitation methods resulted in the loss of diversification and extinction-like dynamics that had not been previously observed. This suggests that environmental conditions may have played a critical role in the evolution of primitive replicators to life-like complexity.
　In this study, we investigated how the intensity and frequency of dilution and agitation, corresponding to the strength of external disturbances, affect the diversity and extinction of self-replicating RNA populations. Using serial dilution experiments and simulations, we found that frequent agitation disrupts frequency-dependent coexistence and reduces population stability by excessively mixing host and parasitic RNAs. Moreover, low RNA concentrations may promote the accumulation of slightly deleterious mutations through genetic drift. We have discovered that frequent agitation obstructs frequency-dependent coexistence of RNAs and lowers population stability by excessive mixing of host and parasite. Furthermore, this low concentration may also promote the accumulation of slightly deleterious mutations due to genetic drift. These results may suggest new conditions for origins of life. These results provide insight into potential environmental constraints relevant to origins of life.