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" Keep in mind a distinction that is being imported into more and more scientific thinking, that between ‘complicated’ and ‘complex’. ‘Complicated’ means a whole set of simple things working together to produce some effect, like a clock or an automobile: each of the components – brakes, engine, body-shell, steering – contributes to what the car does by doing its own thing, pretty well. There are some interactions, to be sure. When the engine is turning fast, it has a gyroscopic effect that makes the steering behave differently, and the gearbox affects how fast the engine is going at a particular car speed. To see human development as a kind of car assembly process, with the successive genetic blueprints ‘defining’ each new bit as we add them, is to see us as only complicated. A car being driven, however, is a complex system: each action it takes helps determine future actions and is dependent upon previous actions. It changes the rules for itself as it goes. So does a garden. As plants grow, they take nutrients from the soil, and this affects what else can grow there later. But they also rot down, adding nutrients, providing habitat for insects, grubs, hedgehogs … A mature garden has a very different dynamic from that of a new plot on a housing estate. Similarly, we change our own rules as we develop. "
― Terry Pratchett , The Globe (The Science of Discworld, #2)
