Two comments:
First, it's misleading to say that the lampreys "haven't evolved". Some of their descendants have a very similar shape to their remote ancestors, that's all you can say. Those descendants may well have changed in many ways that aren't reflected in their morphology, but morphology is all that the fossil record preserves.
Second, if the shape of the lamprey is sufficiently well suited for its ecological niche, evolution will necessarily act to preserve that shape. Lampreys are born all the time with a slightly different shape, but as that shape is less well suited for the niche, those "hopeful monsters" will be weeded out over time.
It really is simple, and almost obvious, if you think about it.
"First, it's misleading to say that the lampreys "haven't evolved". Some of their descendants have a very similar shape to their remote ancestors, that's all you can say. Those descendants may well have changed in many ways that aren't reflected in their morphology, but morphology is all that the fossil record preserves."
I don't know...that sounds pretty weak. Concerning the many changes you speculated about, what kind of things are you referring to? What else is there to a lamprey? There isn't much left when you take out morphology. Eye color or personality?
And think I stated correctly "hasn't changed much" not "hasn't evolved".
Sincerely.
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.
"Second, if the shape of the lamprey is sufficiently well suited for its ecological niche, evolution will necessarily act to preserve that shape. Lampreys are born all the time with a slightly different shape, but as that shape is less well suited for the niche, those "hopeful monsters" will be weeded out over time."
I sure have a hard time understanding how something could maintain an ecological niche through 360,000,000 years of climate fluctuations, catastrophic events, and extinction events.