They still can’t figure out the eyeball in the lowest of species, one on either side of the organism, and usually in front, and on top . . . What blind luck! (Pun intended)
Assuming that eyeballs occurred in random placement all over, the organisms with them placed to give the maximum survival benefit would survive at a higher rate, and reproduce more, passing that trait on to more offspring. Those with eyeballs elsewhere would be eaten before they could reproduce.
Heh very good info and a wonderful pun.