Search on RNA secondary structure landscapes

Search on RNA secondary structure landscapes is distinctly different from search on the spin glass-like models. The difference is a result of the neutral networks that percolate the space. Note that, in practice, the sequences on neutral networks need not have exactly the same fitness, but fitnesses whose differences are below a threshold determined by the mutation rate and noise in the system. As with search on spin glass landscapes, this topic is quite extensive and is reviewed in several papers [39,67,69,113] as well as in Schuster s contribution to this collection, so I will only touch on a few key points. 

The accessibility of many novel structures one point mutation off most neutral nets is not simply a consequence of a net s percolating through sequence space. Different nets could shadow one another to a great extent, limiting the number of different structures easily accessed. Instead, networks meander so that the networks of the vast majority of all common structures are within only one point mutation of at least one point on the networks for every other common structure [64,75], 

Search in neutral net landscapes shows several other properties [110] (i) An evolving population will often split into subpopulations which diffuse independently on different 

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