The concept of machine has dual origins in mechanics and human fabrication. A machine was often taken as any device whose behavior can be explained solely by mechanical laws, and often as any man-made device for performing some task, and often as both. Machine behavior was assumed to be completely determined by such laws, and as a consequence of this, also predictable in principle, for the laws allowed one to calculate its behavior. A paradigm machine having all of these properties was the cuckoo clock which Descartes adopted as a model for living organisms. But insofar as the behavior of organisms is often de facto unpredictable and they remain beyond human fabrication — and biology irreducible to mechanics — any mechanistic thesis that organisms are machines will require a concept of machine which uproots and generalizes its origins, and suitably modifies or rejects the properties of determinism and predictability that were based on them. Thus it was only by assuming that God made the universe that Descartes could claim it was only "a machine in which everything happens by figure and motion".