[general_re]

I've studied it enough to know that an underdeveloped eye will confer no advantage to its holder...

Ponder this, and you will understand your error: "In the land of the blind, the one-eyed man is king."

[plusone]

That is my point. Blind people still have eyes, yet because of some little misconnection, they are left blind. The whole system must work perfectly to be of any use. What good is a 'proto-eye'? If it doesn't work, then it doesn't give the holder any advantage over his rivals.