You're right that it's a little arbitrary. I would stear away from any artificial fitness function. The point of DB is that there is nothing that decides fitness beyond a bots ability to survive, just like in real life.
When you create artificial criteria, you can generally speed up evolution towards that simple goal, but you'll rarely, if ever, see anything really interesting or new that you didn't expect to see.
I dont think you understand me Num.
I did mean there is no fitness function, but to decide which genome to save to disc, you have to make arbitary decisions etc.
I did mean if a certain genome's abundance got over 10 (or so) it would be considered more or less succesful and saved to the genalogical (?) tree, because genome less than 10 would mean it had a hard time to survive.