Evolution - don't anthropomorphise it

All too often we hear people talking about evolution as if has wants and desires, we anthropomorphise genes, assigning goals and thought processes to them.  Genetic material is just doing it's thing, it doesn't know what direction to go in, it doesn't have an end point as a goal. Instead mutations happen. The mutations might be positive, they might be negative or they might not make much difference. The negative mutations are unlikely to lead to a long term change as the organism who have them won't be able to compete as well. The ones that don't do anything might stick around, but equally they might not.  The ones that have positive effects, even if they're only small, are likely to spread through the gene pool, becoming more and more common as the organisms who have them are likely to mate more successfully than those that don't. In order for the organism to end up with a certain complex characteristic each step along the way needs to be beneficial (or at least not detrimental) because there is no way of 'looking at the larger picture', or of having a long term goal, in evolution.

Let's think about the evolution of sight. There was no map showing how to evolve eyes and there are in fact a number of different sight mechanisms found in nature. Insects and humans have very different eyes, for example.

 Eyes evolved through a long process in which mutations gave an organism improved abilities to be aware of it's surroundings.  There was no end goal of developing eyes and a mutation which would theoretically help create eyes in the long term, but which would be immediately detrimental, would not long survive in the gene pool.  It is likely that sight developed initially though a mutation which gave certain cells light sensitivity, enabling the organism to move towards or away from light sources. We can see this response in plants, which don't have eyes but do have an ability to grow towards the light.  There's no specific reason that plants didn't evolve to have eyes, they just haven't accumulated mutations which could lead to eyes in a way that gives the organism an advantage over others.

So when you're thinking about evolution, think about the short term. We can only think about the evolution towards a certain trait in hindsight. Genetic material doesn't know what it's doing.