ALife

The farthest I''ve gotten into Alife is the Game of Life. I would like to do some more with it. I''ve read a post from a few days ago on the same topic, but it didn''t help me much. Take the Helix4 program from necrobones.com, for example. I understand that each cell tries to reproduce itself in a new area of memory, and sometimes mutations occur while doing so. What I don''t know is how does one cell evolve into something more advanced. (What are the kinds of variables needed, like fitness, health, etc?) Ben