A.C.H.  wrote or quoted:

> The argument i was trying to make was more specific then that. I was
> trying to argue that the selection pressure DECREASES when a
> population gets more adapted.
> And because natural selection decreases (though it doesn't stop), a
> state of perfect adaptation (ALL individuals survive a certain
> selection pressure) can not be reached.
> 
> In short:
> - adaptive change decreases natural selection.
> - decreased natural selection decreases adaptive change.

A couple of conventional ideas seem relevant at this point:

In many populations, selection as kept continouosly at a high level.

The population /never/ becomes very fit - since the fitness landscape
deforms underneath it in a manner that penalises the most successful
genotypes in the previous generation.  The selective agents responsible
for this are parasites.

> Therefore the outcome of natural selection will be a state of
> imperfect adaptation, while natural selection is still working on it.

I believe this is widely recognised.  Even populations climbing
well defined adaptive peaks never wind up exactly on top of them.

The phenomenon that causes the effect is known as "mutational load".
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