coding

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 * TODO List**
 * REF: populations evolve to smoother (less rugged) parts of the landscape (REF)
 * REF: initially selected new variants are always very unrobust with respect to wildtypes (REF)
 * See whether we can combine this with the next three pages: "integrating pattern formation", "which code is chosen?" and "what special code evolves?"

=Coding structures=

In the previous section we have discussed the concept of neutral paths and neutral networks and its role in allowing populations to discover novel structures. However, is there mroe going on? i.e. //where do you go on an RNA neutral path? And how neutral is a neutral path?// In other words: **which code evolves?**

One thing that becomes apparent in RNA evolution is that populations evolve to smoother (less rugged) parts of the landscape (REF). So despite neutrality there is still evolution! This is also seen in actual biological system in particular in [|Drosophila] evolution, where it is clear that initially selected new variants are always very unrobust with respect to wildtypes (REF), i.e. they are not yet on a flat part of landscape.

So why does this happen? Well, evolution to higher neutrality allows for more neutral neighbours. As seen in simulations with wildtype tRNA, just in short time spans much more robust structures evolve when secondary structure in the selective pressure. Apparently tRNA is therefore not that robust, probaly because it needs to make conformational changes.

Next: Integrating pattern formation, coding structure and evolution