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Unsourced material may be challenged and removed. In the science of biology, a mechanism is a system of casually interacting parts and processes that produce one or more effects.
Scientists explain phenomena by describing mechanisms that could produce the phenomena. In ecology, mechanisms such as predation and host-parasite interactions produce change in ecological systems. In practice, no description of a mechanism is ever complete because not all details of the parts and processes of a mechanism are fully known. For example, natural selection is a mechanism of evolution that includes countless, inter-individual interactions with other individuals, components, and processes of the environment in which natural selection operates.
The MDC characterization is as follows: mechanisms are entities and activities organized such that they are productive of changes from start conditions to termination conditions. The ontic constituency of biological mechanisms includes entities and activities.