Studies in History and Philosophy of Biological and Biomedical Sciences 43 (2012) 152–163 Contents lists available at ScienceDirect Studies in History and Philosophy of Biological and Biomedical Sciences journal homepage: www.elsevier.com/locate/shpsc The concept of mechanism in biology Daniel J. Nicholson Konrad Lorenz Institute for Evolution and Cognition Research, Adolf Lorenz Gasse, 2, Altenberg A-3422, Austria article info abstract Article history: The concept of mechanism in biology has three distinct meanings. It may refer to a philosophical thesis Available online 2 July 2011 about the nature of life and biology (‘mechanicism’), to the internal workings of a machine-like structure (‘machine mechanism’), or to the causal explanation of a particular phenomenon (‘causal mechanism’). In Keywords: this paper I trace the conceptual evolution of ‘mechanism’ in the history of biology, and I examine how Mechanism the three meanings of this term have come to be featured in the philosophy of biology, situating the new Mechanicism ‘mechanismic program’ in this context. I argue that the leading advocates of the mechanismic program Machine (i.e., Craver, Darden, Bechtel, etc.) inadvertently conflate the different senses of ‘mechanism’. Specifically, Causal explanation they all inappropriately endow causal mechanisms with the ontic status of machine mechanisms, and Function Organization this invariably results in problematic accounts of the role played by mechanism-talk in scientific practice. I suggest that for effective analyses of the concept of mechanism, causal mechanisms need to be distin- guished from machine mechanisms, and the new mechanismic program in the philosophy of biology needs to be demarcated from the traditional concerns of mechanistic biology. Ó 2011 Elsevier Ltd. All rights reserved. When citing this paper, please use the full journal title Studies in History and Philosophy of Biological and Biomedical Sciences ‘Biological Mechanism is committed logically to a great deal as ‘entities and activities organized such that they are productive more than is commonly supposed.’ (Broad, 1925, pp. 91–92) of regular changes from start or set-up conditions to finish or ter- mination conditions’ (MDC, 2000, p. 3). Glennan (2002) and Bech- tel (2006) have also developed their own mechanism accounts. 1. Introduction Glennan defines a mechanism for a behaviour as ‘a complex system that produces that behavior by the interaction of a number of parts, The concept of mechanism has recently received a great deal of where the interactions between parts can be characterized by di- attention in the philosophy of science. The main catalyst for this rect, invariant, change-relating generalizations’ (Glennan, 2002, p. new interest has been the realization that scientists, especially S344), whereas Bechtel characterizes a mechanism as ‘a structure biologists, often refer to mechanisms in their inquiries into the performing a function in virtue of its component parts, component phenomena they investigate. This has led to the development of operations, and their organization’, adding that ‘The orchestrated a lively philosophical research program over the past decade that functioning of the mechanism is responsible for one or more phe- has attempted to make sense of scientists’ ‘mechanism-talk’ and nomena’ (Bechtel, 2006, p. 26). elucidate the role it plays in scientific practice. The standard philo- This emerging mechanism movement aims to provide a new sophical strategy has been to begin by offering a general character- framework in which to tackle a number of classic problems in ization of ‘mechanism’ that captures the way scientists use this the philosophy of science. Central among them is the nature of word, and then show the ways in which mechanisms are involved explanation, in which a focus on mechanisms is deemed to consti- in the explanation of phenomena. The mechanism account that has tute an effective antidote to the outmoded deductive-nomological exerted the greatest influence in the development of this new dis- conception of explanation inherited from logical empiricism. In course has been formulated by Machamer, Darden, and Craver addition, recent literature in the philosophy of science includes (2000). Machamer et al. (MDC, hereafter) conceive mechanisms mechanism-based accounts of causation (Machamer, 2004), E-mail address: [email protected] 1369-8486/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.shpsc.2011.05.014 D.J. Nicholson / Studies in History and Philosophy of Biological and Biomedical Sciences 43 (2012) 152–163 153 reduction (Craver, 2005; Darden, 2005), models (Craver, 2006; (b) Machine mechanism: The internal workings of a machine-like Darden, 2007; Glennan, 2005a), and reasoning in discovery (Bechtel, structure. 2009; Darden, 2006). Moreover, it has been suggested that think- (c) Causal mechanism: A step-by-step explanation of the mode ing about mechanisms may help resolve the problem of underde- of operation of a causal process that gives rise to a phenom- termination (Glennan, 2005a, pp. 458–459), as well as render enon of interest. unnecessary discussions of laws (Glennan, 2002, p. S348; MDC, 2000, pp. 7–8) and theories (MDC, 2000, pp. 16–17). Nevertheless, As this taxonomy illustrates, ‘mechanism’ may refer to (a) a philo- despite the general applicability of mechanism-based philosophy sophical thesis about the nature of life and biology, (b) the work- of science, it is interesting to note that this research program has ings of a machine, and (c) a particular mode of explanation. In developed primarily within the philosophy of biology. Indeed, the order to make the ensuing discussion as clear as possible, I will most prominent defences and extensive elaborations of the mech- refrain from using the word ‘mechanism’ in favour of these three anism approach have been advanced by philosophers interested in terms, employing it only when referring to the word itself and the life sciences, with book-length mechanism accounts now exist- not to any of its meanings. Let us now examine each of the three ing for several biological subdisciplines, including cell biology senses of ‘mechanism’ in more detail. (Bechtel, 2006), molecular biology (Darden, 2006), and neurosci- Mechanicism (often called mechanistic philosophy or mechanical ence (Craver, 2007). This partnership between mechanism-based philosophy) has its roots in the natural philosophy that emerged philosophy and biology is no mere happenstance. In fact, I will from the work and ideas of Galileo Galilei, René Descartes, Pierre show that attending to the role the concept of mechanism has Gassendi, Robert Boyle, Isaac Newton and others during the Scien- played in the development of biological thought opens up a rich tific Revolution. This philosophy is usually associated with a natu- new perspective in which to effectively examine and critically ralistic, atomistic, and deterministic view of nature that tends to evaluate the recent mechanism discourse. lend itself to mathematical characterization. However, biological In a nutshell, what a historically informed perspective reveals is mechanicism, or mechanistic biology, has a rather more specific that the term ‘mechanism’ has come to be used in biology in a meaning (cf. Allen, 2005; Bertalanffy, 1952; Broad, 1925; Dupré, number of different senses. As the new mechanism discourse pro- 2007; Haldane, 1929; Lewontin, 2000; Loeb, 1912; Monod, 1977; ceeds with an almost complete disregard for how the concept of Rosen, 1991; Woodger, 1929). It can be characterized in terms of mechanism has been shaped by the history of its usage, current the following key tenets: discussions frequently suffer from the inadvertent conflation of the different meanings of the term. Admittedly, philosophers are 1. The commitment to an ontological continuity between the liv- generally aware that ‘mechanism’ is a convoluted concept with a ing and the nonliving, exemplified by the quintessential mech- long history, as evidenced by MDC’s assertion that ‘What counts anistic conception of organisms as machines, analogous and as a mechanism in science has developed over time and presum- comparable to man-made artefacts ably will continue to do so’ (MDC, 2000, p. 2). However, most of 2. The view that biological wholes (i.e., organisms) are directly them deem the potential for semantic confusion minimal because determined by the activities and interactions of their compo- they consider the various meanings of the concept to be neatly nent parts, and that consequently all properties of organisms associated with discrete, non-overlapping historical periods. can be characterized from the bottom up in increasing levels Craver (2007, p. 3), for instance, remarks: ‘But what is a mechanism? of complexity History cannot answer this question. The term mechanism has 3. The focus on the efficient and material causes of organisms, and been used in too many different ways, and most of those uses no the unequivocal repudiation of final causes in biological longer have any application in biology’. This paper will demon- explanation strate, in opposition to this claim, how an awareness of the seman- 4. The commitment to reductionism in the investigation and tic breadth of the concept of mechanism afforded by an explanation of living systems examination of its history can help uncover a number of important tensions within the new mechanism discourse, as well as provide Mechanicism has been one of the most influential schools of bio- the necessary