You're not thinking about it properly.
Evolution is a directionless process. To take your example, suppose we have a creature with no visual sense capability (no eyes) at all. For a million generations or so, these creatures managed to survive - they didn't 'need' sight, neither they nor nature 'decided' anything.
One day, one of these creatures underwent a mutation - just one of those random genetic scrambles that can happen in the best of families. This particular mutation turned a few skin cells light-sensitive. They weren't 'eyes' in any meaningful sense of the word, they merely enabled this particular creature to distinguish a slightly darker area from a slightly lighter area. Over time, mostly through trial and error, the creature made the association of food with the slightly lighter area (the things it ate happened to be in the light). And bingo, the mutation turns out to be beneficial. These few light-sensitive cells gave the creature better access to a food source. Being able to eat better means you're likely to stay alive long enough to have offspring, some of which may inherit your mutation. Over time, selection pressure improves the light sensitivity as well as the organization of the cells in question. In another million or billion generations (evolutionary processes are nothing if not patient), you have eyes.
And no one had to decide anything.
Boru
Evolution is a directionless process. To take your example, suppose we have a creature with no visual sense capability (no eyes) at all. For a million generations or so, these creatures managed to survive - they didn't 'need' sight, neither they nor nature 'decided' anything.
One day, one of these creatures underwent a mutation - just one of those random genetic scrambles that can happen in the best of families. This particular mutation turned a few skin cells light-sensitive. They weren't 'eyes' in any meaningful sense of the word, they merely enabled this particular creature to distinguish a slightly darker area from a slightly lighter area. Over time, mostly through trial and error, the creature made the association of food with the slightly lighter area (the things it ate happened to be in the light). And bingo, the mutation turns out to be beneficial. These few light-sensitive cells gave the creature better access to a food source. Being able to eat better means you're likely to stay alive long enough to have offspring, some of which may inherit your mutation. Over time, selection pressure improves the light sensitivity as well as the organization of the cells in question. In another million or billion generations (evolutionary processes are nothing if not patient), you have eyes.
And no one had to decide anything.
Boru
‘I can’t be having with this.’ - Esmeralda Weatherwax
