One question often asked here is this: “How do these different parts ‘know’ that they belong to the same unit?” In a literal sense, this is a fallacious question, as the parts cannot “know,” but it is an interesting question from the heuristic point of view, as it obliges one to think in terms of systems biology, as well as in terms of cooperation in evolution, since these parts clearly have “learned” to positively interact with each other due to natural selection and adaptive pressure.
