Mechanism (biology)
Encyclopedia
In biology --and in science in general-- a mechanism is a complex object (system
) or, more generally, a process
that produces a regular phenomenon. For example, natural selection is one of the mechanisms of biological evolution
, other being genetic drift
, biased mutation, and gene flow
; competition
, predation
, host-parasite interactions
, etc. are mechanisms of community
structuring; and membrane depolarization is the mechanism of transmission of neural signals
.
Accordingly, descriptions of mechanisms are a part of an answer to a question about why some object or process occurred. In other words, descriptions of mechanisms occur in explanations of biological facts. Thus, mechanism refers back from the object or process, along some chain of causation. No description of mechanism is ever complete. For example, the mechanism of sunlight
might include the rotation of the earth, the Earth's orbit, the sun, nuclear reactions, heat, temperature, radiation emission, electromagnetic theory about the propagation of light, formation of the solar system, etc. Compare this to the function
of the object or process, which looks forward along some chain of causation to a goal or evolutionary success.
Many characterizations/definitions of mechanisms in the philosophy of science
/biology have been provided in the past decades. For example, one influential characterization of neuro- and molecular biological mechanisms is: mechanisms are entities and activities organized such that they are productive of regular changes from start to termination conditions (Peter Machamer, Lindley Darden
, & Carl Craver 2000; 'MDC' hereafter). Other characterizations have been proposed by Stuart Glennan (1996, 2002), who articulates an interactionist account of mechanisms, and William Bechtel
(1993, 2006), who emphasizes parts and operations (cf. MDC).
Mechanisms in science/biology have reappeared as a subject of philosophical analysis and discussion in the last several decades due to a variety of factors, many of which relate to metascientific issues such as explanation and causation. For example, the decline of Covering Law (CL) models of explanation, e.g., Hempel's deductive-nomological model, has stimulated interest how mechanisms might play an explanatory role in certain domains of science, 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 proposes an ontic view of what he calls "causal-mechanical" explanation, namely that explanations are in the world. There are two kinds of ontic explanation: etiological and constitutive. While Salmon focuses primarily on etiological explanation, with respect to which one explains some phenomenon P 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 mechanism M that is productive of (or causes) P. Indeed, whereas (a) Noam Chomsky
differentiates between descriptive and explanatory adequacy, where the former is defined 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 metascientific context of mechanisms, descriptions and explanations seem to be identical. This is to say, to explain a mechanism M just 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").
Ontic aspect
Descriptive aspect
Epistemic aspect
System
System is a set of interacting or interdependent components forming an integrated whole....
) or, more generally, a process
Process (science)
In science, a process is every sequence of changes of a real object/body which is observable using the scientific method. Therefore, all sciences analyze and model processes....
that produces a regular phenomenon. For example, natural selection is one of the mechanisms of biological evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
, other being genetic drift
Genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
, biased mutation, and gene flow
Gene flow
In population genetics, gene flow is the transfer of alleles of genes from one population to another.Migration into or out of a population may be responsible for a marked change in allele frequencies...
; competition
Competition
Competition is a contest between individuals, groups, animals, etc. for territory, a niche, or a location of resources. It arises whenever two and only two strive for a goal which cannot be shared. Competition occurs naturally between living organisms which co-exist in the same environment. For...
, predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
, host-parasite interactions
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
, etc. are mechanisms of community
Community (ecology)
In ecology, a community is an assemblage of two or more populations of different species occupying the same geographical area. The term community has a variety of uses...
structuring; and membrane depolarization is the mechanism of transmission of neural signals
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
.
Accordingly, descriptions of mechanisms are a part of an answer to a question about why some object or process occurred. In other words, descriptions of mechanisms occur in explanations of biological facts. Thus, mechanism refers back from the object or process, along some chain of causation. No description of mechanism is ever complete. For example, the mechanism of sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
might include the rotation of the earth, the Earth's orbit, the sun, nuclear reactions, heat, temperature, radiation emission, electromagnetic theory about the propagation of light, formation of the solar system, etc. Compare this to the function
Function (biology)
A function is part of an answer to a question about why some object or process occurred in a system that evolved through a process of selection. Thus, function refers forward from the object or process, along some chain of causation, to the goal or success...
of the object or process, which looks forward along some chain of causation to a goal or evolutionary success.
Many characterizations/definitions of mechanisms in the philosophy of science
Philosophy of science
The philosophy of science is concerned with the assumptions, foundations, methods and implications of science. It is also concerned with the use and merit of science and sometimes overlaps metaphysics and epistemology by exploring whether scientific results are actually a study of truth...
/biology have been provided in the past decades. For example, one influential characterization of neuro- and molecular biological mechanisms is: mechanisms are entities and activities organized such that they are productive of regular changes from start to termination conditions (Peter Machamer, Lindley Darden
Lindley Darden
Lindley Darden is a contemporary philosopher of science, with a research focus on the philosophy of biology. She received her Ph.D. from the University of Chicago in 1974 and B.A. in 1968 from Rhodes College, and is currently Distinguished Scholar Teacher at the University of...
, & Carl Craver 2000; 'MDC' hereafter). Other characterizations have been proposed by Stuart Glennan (1996, 2002), who articulates an interactionist account of mechanisms, and William Bechtel
William Bechtel
William Bechtel is a professor of Philosophy in the Department of Philosophy and the Science Studies Program at the University of California, San Diego. He was a Professor of Philosophy at Washington University in St. Louis from 1994 until 2002...
(1993, 2006), who emphasizes parts and operations (cf. MDC).
Mechanisms in science/biology have reappeared as a subject of philosophical analysis and discussion in the last several decades due to a variety of factors, many of which relate to metascientific issues such as explanation and causation. For example, the decline of Covering Law (CL) models of explanation, e.g., Hempel's deductive-nomological model, has stimulated interest how mechanisms might play an explanatory role in certain domains of science, 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 proposes an ontic view of what he calls "causal-mechanical" explanation, namely that explanations are in the world. There are two kinds of ontic explanation: etiological and constitutive. While Salmon focuses primarily on etiological explanation, with respect to which one explains some phenomenon P 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 mechanism M that is productive of (or causes) P. Indeed, whereas (a) Noam Chomsky
Noam Chomsky
Avram Noam Chomsky is an American linguist, philosopher, cognitive scientist, and activist. He is an Institute Professor and Professor in the Department of Linguistics & Philosophy at MIT, where he has worked for over 50 years. Chomsky has been described as the "father of modern linguistics" and...
differentiates between descriptive and explanatory adequacy, where the former is defined 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 metascientific context of mechanisms, descriptions and explanations seem to be identical. This is to say, to explain a mechanism M just 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").
Characterization
The MDC characterization is: mechanisms are entities and activities organized such that they are productive of changes from start conditions to termination conditions. There are three distinguishable aspects of this characterization:Ontic aspect
- The ontic constituency of biological mechanisms includes entities and activities. Thus, the MDC conception postulates a dualistic ontology of mechanisms, where entities are substantial components, and activities are reified components of mechanisms. This augmented ontology increases the explanatory power of the MDC conception.
Descriptive aspect
- Most descriptions of mechanisms (as found in the scientific literature) include specifications of the entities and activities involved, as well as the start and termination conditions. This aspect is mostly limited to linear mechanisms, which have relatively unambiguous beginning and end points between which they produce their phenomenon, although it may be possible to arbitrarily select such points in cyclical mechanisms (e.g., the Krebs cycle).
Epistemic aspect
- Mechanisms are dynamic producers of phenomena. MDC emphasize activities, which are, essentially, causes that are reified. It is because of activities that the MDC conception of mechanisms is able to capture the dynamicity of mechanisms as they bring about a phenomenon.