A moral rule that is good to follow now may be maladaptive at some future date because the situation changes.

As is true of the Biblical injunction against "spilling your seed."

But your comments about morals becoming maladaptive do not, I think, get at the bugaboo of modern times, i.e. whether morals should be absolute for an entire society or whether they can be relative to the individual.

(or is "relativism" so last week? I have lost touch, no longer able to engage in collegiate bull sessions -- except on Slate.)