posted by brooke .
Explain how early RNA molecules might have been able to respond to natural selection?
Try your later post because I saw it first.
It is probable that a multitude of RNA sequences can function as replicase ribozymes. However, since the sequences would be different, the RNA molecules would have different properties. For example, some of them could be more stable than the others, or replicate more quickly, or more accurately, and so on. No sequence is likely to have 100% fidelity in copying, so mistakes will crop up.
Any copying mistakes that turned out to be beneficial under the prevailing conditions would lead to the parent ribozyme making a greater number (or more stable, etc.) ribozymes, and would tend to be preserved and increase in frequency.
Any copying mistakes that hindered replication (or made the molecules less stable, etc.) would tend to cause those sequences to become less frequent in future 'populations'.