This guy, Andrej Karpathy (http://karpathy.ca/) made an enormous job an built an open source artificial life simulation, which is very successful and focused correct variables among the other similar projects.
The clip showing hunting pack behavior, http://www.youtube.com/watch?&v=RjweUYtpNq4&t=3m17s, really makes them come alive, almost like they'll run off the page. Chilling. Reminds me of George Martin's "Sandkings" (don't go to Wikipedia, read the full story).
Since this is open source, i think this could be a good start to build a way more complex artificial world, like three dimensions, similar earth conditions (temperature, wind, terrain specifications etc.)
I think the main point to build such an artificial world is to give a start of the life of a creature, which surprises it's own creators with it's behaviors.