it's all local.
This is why I asked that people explain why a particular mutation would be selected for - to explain the conditions that cause it to be beneficial.
This is a very important point and one that IMHO is not explained often enough. There really is more than one mechanism in evolution. Mutations are not beneficial, or harmful in and of them selves. It's only the outcome that gives us any indication of benefit or harm.
Likewise, Natural Selection can only be understood based on the results. Whether the outcome is beneficial or harmful depends on the point of view of the observer.
We realy need to see the system as in constant flux, constant change. We are always looking back at a history, looking at what happened. Not only do the conditions change, but any given set of conditions will be both beneficial for some and harmful to others. Just as on the mutation side, Natural Selection is only harmful, beneficial or neutral in relation to the particular point of view of the observer.
Aslan is not a Tame Lion