some ideas for small artificial life prog?

I'm going to work on an artificial life program in LISP.  Text-based, will write the parser-renderer in C later.  I've seen a lot of AL programs; being just grandiose state machines I'm pretty sure writing one would be within my capabilities.

...but I don't want to write a cookie-cutter one either that's just full of animals eating each other and mutating.  I'm not looking to write Spore, but I am seeking some ideas.  What are some concepts that haven't been explored too deeply in AL programs that would be interesting to see attempted?