Evolution doesn't work like that.
Imagine the first clump of cells that stayed stuck together due to a mutation. At first moving around was nearly impossible. Later they probably lined up better and were able to move better. Next a subset of them in a position better able to move became dedicated to do it because that saved energy. As these traits spread throughout the population they got better at finding food. This meant that they could grow bigger. That single part of them that could move slowly changed shape and position, until it was a proto-fin.
(That is not 100% how it happened and I skipped a lot of steps, its just an example)
For a trait to spread throughout a population it must be useful. That trait also doesn't know what it will become. All of the traits evolve at once so they must have been useful in a less evolved form if they exist in that one.
Sorry I'm having a hard time understanding it. Are you saying that these mutations are sort of independent of the larger organism? As in, the mutation is just trying to improve itself not the entire organism it's part of? And so any benefits caused by that mutation to the entire organism is just by chance?
I don't know if this is right or if it makes sense though
The creation of each part is controlled by the genes. As the genes change the part is made differently. As long as the change gives a survival advantage the change spreads throughout the population by breeding.
"Are you saying that these mutations are sort of independent of the larger organism? "
Would a mutation that changes your eye color do anything to the rest of your body? Probably not, but it still might give a small breeding advantage.
"And so any benefits caused by that mutation to the entire organism is just by chance?"
yes mutations are random. More often than not they hurt the organism.
Thanks for your responses I think I understand it a bit better now