I think a lot of people have trouble discussing this because they're going back along one line - the line from the lamprey we know today versus the fossil record of 360 million years ago. If we start from the fossil record and move forward, it's easier to describe it in terms of one line remaining relatively unchanged over time because it hasn't had much pressure to change, while other descendants have indeed shown some evolutionary influences due to mutations that have proved equally or more successful compared to the original model.
Ok, I'll warn you now so you can call me names ahead of time - I'm going to post and run, because I can't strand my son at school.
Here's my comment: I've seen in this thread the one common theme I've seen from all evolutionists - no matter what the fossil record shows, it supports evolution.
Think about it. All of these have been proposed on this one thread: 1) If there are changes, that must mean evolution. 2) If there are no changes, that must mean evolution. 3) If this branch didn't change, others must have, so that must mean evolution.
So: None of us were there, and the evidence is approached from a foregone conclusion. My conclusion just happens to be based on God, and whether any will admit it or not, He's better able to do the job than chance.
Flame away, but like I said, I gotta go.