 | This articlemay beconfusing or unclear to readers. Please helpclarify the article. There might be a discussion about this onthe talk page.(September 2007) (Learn how and when to remove this message) |
 | This articleneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Mechanism" biology – news ·newspapers ·books ·scholar ·JSTOR(December 2013) (Learn how and when to remove this message) |
Inbiology, amechanism is a system of causally interacting parts and processes that produce one or more effects.[1]Phenomena can be explained by describing their mechanisms. For example,natural selection is a mechanism ofevolution; other mechanisms of evolution includegenetic drift,mutation, andgene flow. Inecology, mechanisms such aspredation and host-parasite interactions produce change inecological 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.
Many characterizations/definitions ofmechanisms in thephilosophy of science/biology have been provided in the past decades. For example, one influential characterization of neuro- and molecular biological mechanisms byPeter K. Machamer,Lindley Darden andCarl Craver is as follows: mechanisms are entities and activities organized such that they are productive of regular changes from start to termination conditions.[2] Other characterizations have been proposed byStuart Glennan (1996, 2002), who articulates an interactionist account of mechanisms, andWilliam Bechtel (1993, 2006), who emphasizes parts and operations.[2]
The characterization by Machemer et al. is as follows: mechanisms are entities and activities organized such that they are predictive of changes from start conditions to termination conditions. There are three distinguishable aspects of this characterization:
Mechanisms in science/biology have reappeared as a subject of philosophicalanalysis and discussion in the last several decades because of a variety of factors, many of which relate to metascientific issues such asexplanation andcausation. For example, the decline of Covering Law (CL) models of explanation, e.g., Hempel'sdeductive-nomological model, has stimulated interest how mechanisms might play an explanatory role in certain domains ofscience, especially higher-level disciplines such as biology (i.e., neurobiology, molecular biology, neuroscience, and so on). This is not just because of the philosophical problem of giving some account of what "laws of nature," which CL models encounter, but also the incontrovertible fact that most biological phenomena are not characterizable in nomological terms (i.e., in terms of lawful relationships). For example, protein biosynthesis does not occur according to any law, and therefore, on the DN model, no explanation for the biosynthesis phenomenon could be given.
Mechanistic explanations come in many forms.Wesley Salmon proposed what he called the "ontic" conception of explanation, which states that explanations are mechanisms and causal processesin the world. There are two such kinds of explanation:etiological andconstitutive. Salmon focused primarily on etiological explanation, with respect to which one explains some phenomenonP by identifying its causes (and, thus, locating it within the causal structure of the world). Constitutive (or componential) explanation, on the other hand, involves describing the components of a mechanismM that is productive of (or causes)P. Indeed, whereas (a) one may differentiate between descriptive and explanatory adequacy, where the former is characterized as the adequacy of a theory to account for at least all the items in the domain (which need explaining), and the latter as the adequacy of a theory to account for no more than those domain items, and (b) past philosophies of science differentiate between descriptions of phenomena and explanations of those phenomena, in the non-ontic context of mechanism literature, descriptions and explanations seem to be identical. This is to say, to explain a mechanismM is to describe it (specify its components, as well as background, enabling, and so on, conditions that constitute, in the case of a linear mechanism, its "start conditions").