I'm confused. Isn't that the way it would have to be?

lunar_mycroft 34 minutes ago | parent [-]

(Going from memory here)

No, it's possible that there's a single gene that would do it, meaning a single mutation would enable it. But that's not what happened here. Instead, there were multiple genes involved, with some of the necessary mutations occurring long before the other.

	▲	vidarh 2 minutes ago \| parent [-]
		But when multiple genes were necessary, you would still expect the whole chain to be present in those who eventually got the final mutation, or it wouldn't have done anything. So it is still what you would expect.