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.
The mere fact that they even had that design, times 2, and would be linked to a central processing area that would provide the overall organism with a method to "see" what's going on, makes Darwin look like a jackass
I could use an eyeball on my palm. It could be stuck up above tall grass and bushes to look around, it could be shoved in a hole, peek around a corner, slipped underwater. It would be a huge advantage. But no, when I stick my head in a cave, a tiger bites it off.
>>Assuming that eyeballs occurred in random placement all over<<
That’s quite an assumption. Vegas would love those odds:)