Thunder - doesn't that seem to be asking what the difference between a heap and a pile.
If we add one grain of sand is it now a pile - how about now?
You would have to define 'eye' and then define 'sight' and then have a pretty firm necessary and suficcient definition for the difference between sight and non sight.
TTF
Ok...eyeballs, which it seems most creatures have, larger animals I guess (around rabbit-size and up)...what did the first eyes look like, how did they eventually evolve to what they are today?
