It's not done by intervention of some superior intelligence. In most cases it's all there to begin with and we just need to know how to activate the system to get dramatic results.
Well, I didn't mention "superior" intelligence. I think Rupert Sheldrake put it in an interesting way when he said Nature develops habits. So the makeup of an organism is not "thought out" in the sense that some conscious entity has to be thinking, "this cell goes here, that one goes there". That would be ludicrous. If intelligence is indeed involved in the creation of organisms, then I would be inclined to think it happens in a similar way as the development of other intellectual efforts, such as language, culture, and science. For the most part, those things come about by chance.
"Woah", you might be thinking, "what is the matter with this guy?" So let me explain. Most of the time, we don't discover things by thinking them out, we sort of "hit upon" them by what seems like chance. But that is not equivalent to saying intelligence is not required. Intelligence is involved in the selection of which chance discoveries are worth keeping, worth becoming habits to speak in Sheldrake's lingo.
That is, after much ado, what I think about evolution. Yes, organisms evolve and DNA plays a key role in it. But DNA is the raw material, not the blueprint. The blueprint for an organism also evolves, but as a process of choices between multiple possibilities discovered by chance but selected with a clear goal in mind. And the goal is not survival. As human beings we know full well that surviving is what we need, not what we want. What do we want? It's written on the wall: love, beauty, happiness.
Of course the die-hard evolutionists will turn their intuition around and say that things like love, beauty, happiness, are just games played on us by our genes so that we find motivation to survive. I say that is Language Removed, and I hope you can understand why I think that way now.
All the best,