[AndrewC]

This shows a complete misunderstanding of the concept of inheritance. Neutral sequences would be preserved, since they are not selected positively or negatively.

Are negative sequences preserved?

[shubi]

Sequences that give even a small percent disadvantage in survival eventually get eliminated. But if the environment changes, they might become positive and reverse the process.

This is what we observe with sickle cell anemia in malarial areas.