Ok, I've taken this thread off topic enough right now... now on topic.
I think it would be bad to make a transfer from the cell level to land without water in between, but I also wouldn't mind it if they took out underwater cities. I think you should be able to go underwater for as long as you want in the creature stage, but in order to move on to the tribe stage, you should have to move onto land. Then, if someone wanted to, they could live underwater for most of the creature stage, and when they want to move on, they must grow legs and feet to walk onto land.