The promiscuity and degeneracy of ten unique RNA base-pairing rules can determine the success of adaptive RNA evolution.

RNA base-pairing rules strongly shape adaptive evolution on RNA secondary-structure fitness landscapes, with A-U, G-C, G-U enabling over 80% of evolving populations to reach global peaks.

• Why it matters: Fitness landscape topography depends on how genotype changes affect RNA phenotypes, but the role of biochemical base-pairing rules in shaping genotype–phenotype maps is unclear.
• What they did: Computationally, secondary-structure genotype–phenotype maps were built for RNA under all ten RNA base-pairing rules, then adaptive evolution was simulated where fitness equaled secondary structure.
• The result: The base-pairing rule alters the probability of finding the global peak, and simple map features like the fraction of genotypes that are local peaks predict this likelihood via promiscuity and degeneracy.

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