This will be cool for db3.
This has been on my mind since 2005. Thinking about it all this time, I've come to the conclusion that I think it's outside the scope of Darwinbots. Here's why: in the real world, metabolism is highly conserved. The way we break down or build up sugars and proteins and fats is pretty much the same way that a yeast does. That is, metabolic pathways evolved once, billions of years ago, and ever since it's been the base level on to which everything else is built. In a certain sense, it's like the OS life is written for.
Darwinbots is more about behavior than ability. That is, the DNA scripts we write are concerned with when to shoot, or reproduce, or spin, or move, and not how. Evolving metabolism is fundamentally a question of how. Once you know how, that is, once the metabolite graph has been mapped and you know the most efficient ways to get from A to Z, anything outside that pathway is "wrong". So bot authors would know the "correct" solution and always use it. Evolved bots would have to figure it out, but it's just an arbitrary hoop to jump through before you can get to the far more interesting questions of strategy and how to compete against other bots.
Not to say that I don't think this sort of thing is interesting. It is. But it's not interesting in a gameplay sense. It's interesting in a computer science sense. There's an arbitrary directed graph and you want to find the most efficient nodes to do certain things, and the best ways between them. That's a problem, and there's a specific solution, and finding the solution is non trivial. But once you have it, you have it and it's done and solved. Contrast that with deciding when to reproduce. There's no "right" solution. Each choice of when to reproduce carries with it different strategies and implications, and it works to create an gameplay decisions for bot writers, and an interesting landscape for bots to evolve on.
Again, I do agree with nums...Metabolism is one of a few factors which make DNA about the HOW something happens...Really, Im still rooting for us to just get chemicals in the feild. Then we get both CS and GP fun. Bots right now just swim in a small sterile enviroment, with a couple of visible pods of food.