[VadeRetro]

No, I'm just busy laughing.

D.O.A. (Delusions of Adequacy)

What is the barrier that prevents "microevolutionary" changes from accumulating indefinitely to "macroevolutionary" in reproductively isolated populations? (Note that an arbitrary distinction cannot function as a real-world barrrier.)

[Aquinasfan]

What is the barrier that prevents "microevolutionary" changes from accumulating indefinitely to "macroevolutionary" in reproductively isolated populations?

The minor problem of the lack of fossil evidence, your example of the shell notwithstanding. The thing is, all of the fossil record should show transitional forms. Stable morphology should be a rare exception, rather than the rule.

[gore3000]

You know those shells are nice. However, if you are using them to prove evolution you are sorely deluded. You see, shells are made by the organism to protect itself. They are not part of the organism. It is like trying to prove the evolution of beavers by showing their dams!