If I Had Multiple Faces
This is exactly the kind of thing I envisioned when I learned about the scripting ability in Second Life, and again when I heard about Multiverse (a build-your-own MMO type thing). I never even got to try making it happen because my lappy can barely handle SL and Multiverse isn't out yet.
In the beginning, Linden Lab created the heavens and the earth, but the sky was empty and the land was barren. The trees were green but did not grow, the sun and wind passed overhead but did not affect them.
Then Laukosargas Svarog came upon this and said, Come, let us make clouds so that they can be borne upon the wind. She did, and it was good. Then Laukosargas said, Let these clouds cast rain upon the ground, and where the land is marshy, let marshy flowers bloom, and where the land is open, let open flowers bloom. And let the sun shine upon these, and where the sun shines brightest, let them grow more, and where it shines least, let them lay fallow. This she also did, and it was good. Seeing this, Laukosargas said, Let bees fly amongst these flowers to pass their seed between each other, and thus be fruitful and multiply. Then she said, Let there be birds to feast upon the seeds, lest these flowers be too fruitful and multiplicitous. This she did as well, and it was likewise good.
Then her computer crashed. And that was not so good.
That quote's from this article I read on New Worlds Notes, a Second Life news blog. Basically, this lady made an artificial ecology. All the "life" (I'm not optimistic enough to drop the quotes yet) on her island is interdependent of the other organisms in the system. It's a beautiful thing.
The article even mentions emergence, which is my big area of interest lately. I totally recommend checking out the article or even Second Life. Your first account is free.