Evolution just does it's own thing. What may seem like predictability really isn't. There have been suggestions, as you might expect, that evolution has targets, that it's designed to get to certain types of beings.
There was a great rebuttal to this several years ago by the biologist P.Z. Myers. It goes kind of like this:
Look at the amazing way that evolution has shaped animals that swim fast through water. Sharks are like super-streamlined missiles, as are barracuda. Now look at the dolphin - apart from the angle of fins in the tail, it's the same super-fish-shape as the shark. The fish shape is a great example of convergent evolution, of how evolution will reach the same designs for the same situation. Hold on a minute, there's something moving very fast through the water over there - it's a squid. Oops!
Convergent evolution can happen, but it's not inevitable. There are sharks, dolphins... and squid!