Chemistry

There are two sources of energy in the dish: food, and the atmosphere. The atmosphere contains four chemical elements:

• Three primary elements: Oxygen (O), Hydrogen (H), and Nitrogen (N).
• A catalyst, also called "Element X", or simply X.

The rules of breathing are complicated, but the result is simple. First, here are the rules:

1. Each narjillo can breathe one of the primary elements, depending on its dominant color: a narjillo that is mostly red will breathe O, a narjillo that is mostly green will breathe H, and a narjillo that is mostly blue will breath N.
2. As it breathes, the narjillo converts its primary element to another primary element. This byproduct element is determined by the narjillo's genes. For example, a narjillo that breathes O can convert either O->H, or O->N. And then there are four other possible cycles: H->O, H->N, N->O and N->H. None of the primary elements can ever be created or destroyed-it can only converted to another primary element. This means that the amount of O, H, and N in the atmosphere varies all the time, but the total sum of O+H+N is a constant.
3. A narjillo can never convert a primary element into itself. A narjillo that is born with a genome that converts O->O, H->H or N->N is out of luck, and cannot breathe at all.
4. As it breathes, the narjillo gains energy. The amount of energy it gains is proportional to the current density of the element it's breathing. For example, if the atmosphere is mostly N, then a narjillo that breathes N can live and prosper on breathing alone, even without ever eating food. On the other hand, if the atmosphere is mostly O and H, then a narjillo that breathes N gains little or no energy from breathing. It needs to reach food, or it will die quickly as it spends its energy to move or lay eggs. (Alternately, it can live a long boring life by never moving or laying eggs-but this means that it eventually die without leaving descendants, and its genome will go extinct).
5. Wait, we didn't talk about element X yet. X has a special role: it is never converted to or from anything, but all narjillos consume X during their breathing cycle to extract energy from the conversion of O, N or H. If there is no X available, then narjillos cannot gain energy while breathing. Luckily, there is a constant amount of X in the atmosphere, that is continuously refilled. This fixed amount of X is divided across all narjillos in the dish at every tick. This means that if there are just a few narjillos, they will get a lot of X, and they will breathe very efficiently. As the number of narjillos rises, the amount of X available for each individual drops, and all creatures become less efficient at breathing. They will still convert the primary elements into each other, but they won't extract much energy from this conversion.

Complicated rules, as I told you-but the outcome is simple: Narjillos help each other breathe in a closed-cycle ecosystem. It works like this: imagine that a species of narjillos evolves, that converts O to N. This species will quickly exhaust all the O in the atmosphere, and become unable to breathe effectively. On the other hand, if the dish contains a second species that converts N to O, then the two species can reach a stable equilibrium, where they both can prosper. Each species will consume its own favourite element, and convert it to the element that the other species needs to survive. On the other hand, all individuals of both species need X to breathe, and X is a fixed, limited resource. This means that the two species cannot reproduce indefinitely: too many individuals would consume all the available X, and become unable to breathe. The result is a balanced ecosystem where each especies benefits from the existence of other species, and no species can take over the entire dish without undermining its own ability to breathe.

Breathing is not strictly necessary. A narjillo could survive and reproduce successfully without breathing, as long as it gets a lot of energy from food. But reaching food requires movement, that consumes energy. So a species has to evolve its own way of gaining energy, which usually involves either moving a lot to reach food, or standing very still to spare energy, and get energy from the atmosphere-or any combination of the two.