So... is the top answer incomplete?

Bingo. I feel like I'm able to detect a yellowish tint in my urine stream if I'm dehydrated. Maybe I'm mistaken... but am I?

Given your explanation, would it be fair to say that species like that are "evolving in place?"

That is, they're still actively mutating, but the mutations are "undone" in successive generations.

I know I've simplified things a lot, but is this still a serviceable explanation of the concept?