“Evolution,” “natural selection,” and “mutation” are different things. When we start to confuse them, we get into real trouble.
When most people talk about evolution, they look at it as teleological… goal directed. The idea of design is especially tempting if one starts by thinking “the organism somehow wants to see, or is developing specifically so that it can see (or hear, or think, or whatever).”
Organisms don’t “want,” in that sense, to evolve. Human beings might want things, but certainly amoebae do not.
Another problem is that people look at mutations, and think that evolution is random. Mutations may be random (again, cells don’t “want” to evolve), but natural selection is not. If a mutation causes one to have slightly better sight, and all other variables remain the same, one is probably going to outlast one’s competitors. One will probably breed more, and pass the genes on for better eyesight.
Again, this isn’t goal directed… if better eyesight meant that more neurons were being used to process sight, and less were being used to process sound, and the environment is very sound-rich and light-poor, the likelihood of better sight genes surviving is small. Further, even if the better sight genes aren’t selected away, if they don’t provide some breeding advantage (either through longevity, attractiveness to mates, or increased fertility), the genes won’t establish their own line.
We’re also at a very late point in evolution. Mutations occur all the time, but the vast majority of them result in still births or defects that don’t provide any reproductive advantage to the organism. Early life forms, necessarily crude, had a lot of possible permutations to go through that would lead to more efficient fuel processing and reproduction. The longer a species survives in an environment, the less likely it is that a given mutation will be useful to it. Further, the more complicated it is, the more likely a given mutation is to disturb other processes that are going on within the organism.
So, take away points:
- Evolution is not goal directed, or teleological.
- Evolution is not random… it is a combination of mutation and natural selection.
- The longer a species survives in a given, unchanging environment, the less likely it is that a new mutation will be beneficial. Rapid environmental change may mean that mutations might be beneficial that otherwise would not have been, but once a certain level of complexity is reached (think dinosaurs), the amount of genetic change that would be required is so great that mutations are unlikely to happen on that scale, and the species is likely to die out.