Introduction. The theories of function and the current issues

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  1. The theories of function and the current issues.

This collection of papers aims at reflecting upon the metaphysics of function and the various problems that functional explanations raise. The question of function and functional explanations has for sure been extensively dealt with by philosophers of biology, as well as by philosophers of action and philosophers of mind. Since the early 70s, the concept of function, as used in biology, psychology, and related disciplines, has indeed continuously been under philosophical scrutiny. The origin of these discussions is to be found in the two papers published by Larry Wright and Robert Cummins in 1973 and 1975 respectively. These papers renewed the debate with two innovative analyses going different directions. The etiological theory of functions (or “selected effects” functions (Neander, 1991), or “teleofunctions”, or “proper functions” (Millikan 1984)), which stems from Wright's paper, holds a realist conception of function, and in the case of Wright himself aims at a unified theory of artifacts and biological entities. Against this realistic claim, Cummins defended a conception of functions (as “causal role” in a system) that makes them relative to an explanatory strategy, which has to define a system within which the functional item is embedded. Both acknowledge that “function” is a concept used in some kinds of explanation, but they diverge from the first step, because the etiological account thinks that the function of X being Y explains the presence of X, whereas for the causal role theorist the function of X being Y explains or contributes to explain the general proper activity of a system which includes X.
The etiological theory faced several objections and has been refined through numerous debates in the two last decades (e.g. Godfrey-Smith 1994, Kitcher 199*, Buller 199*, etc.). Similarly, the causal role theory of functions increased in sophistication, as researchers were finding new patterns of explanation which made use of it for particular cases, for example when Amundson and Lauder (1990) emphasized its major role in functional morphology. Given that the two analyses seemed to be adequate in distinct areas of biology, and that, moreover, those two analyses accounted for different functional ascriptions of a same item that could be met in one given field of this science, important papers such as Kitcher (1993), Millikan (1989) or Godfrey-Smith (1994) considered ways of articulating the two approaches, and many authors subscribed to some sort of pluralism. So even though the two conceptions rest on opposite assumptions – especially, as mentioned above, about what the explanandum of a functional explanation should be – they situate sets of nuanced views rather than two monolithic positions; and those two sets are such that in each of them pluralist positions are easy to be found.
In broad outline, the two following claims about functions make up the general framework for the discussion: (a) Functions are generally implemented in mechanisms; (b) functional explanations in biology have an essential relation with natural selection. Each main account of functions emphasizes one aspect, and downplays the other. For instance, when one says that (F) “the function of the vertebrate eye is seeing”, this relates in the same time to two sets of facts: there is a vision mechanism, quite sophisticated, involving at least the eye, nerves and the brain – and the eye is the result of a complicated process of natural selection across vertebrates, first sketched by Darwin in the chapter * of the Origin of species, and lastly modeled by Nilsson and Pelger (1989). Understanding what functions and functional explanations are therefore requires one to take a stance regarding these two aspects. An etiological theorist will claim that the main aspect is the natural selection, which accounts for the explanatory role of the statement (F) regarding the presence of the eye; and she can account in the same manner for functions of items which involve a very crude mechanism, for example the fur colour of tigers. Yet there is also a thin mechanism here (the fur makes the tiger match its surroundings, so the preys have fewer chances to see it), even if it is far less complicated than the vision mechanism. Inversely, the causal role theorist will emphasize the first aspect, the mechanism, and on this basis account for the explanatory role of F regarding the general perceptual ability of the vertebrate. Then, as soon as items involve some mechanisms, the embedding of such mechanism in a large system will ground a functional statement understood in causal-role terms, even if no uncontroversial selection has been acting, or if the item has been demonstrated to be the outcome of drift or a mere byproduct of selection. Pluralist positions – namely, etiological theory that, within the continuum of etiological positions, do not tie the whole account to the fact of selection (e.g. Buller, *; Kitcher, *), or causal-role theorists who admit that mechanisms are there because of natural selection, to which they owe many features – will be more likely to make room for both aspects, and tackle the issue of their articulation (in general, and in each distinctive field). Given that the reflection on functions and functional explanations, in philosophy and in life sciences at least, got so sophisticated and allowing for many pluralist stances founded in both sides, this urges for a renewed understanding of the possible relations between (a) and (b).

The title of the present collective book is therefore: Function: selection and mechanisms. This book is intended to cast new light upon the two rough claims (a) and (b), by testing them through their confrontation with scientific developments in biology, psychology, and recent developments in metaphysics.

In effect, various developments in biology, engineering, cognitive sciences and philosophy of science compel us to think that, notwithstanding the degree of sophistication reached by philosophical theories of function in the end of the ‘90s, issues about functions are not yet solved. The framework of the philosophical understanding of function and functional explanation has been actually changed by the following advances.

  • A. Regarding philosophy of science strictly speaking, a new position has been defined in the context of the debates about causation and explanation, which has been called “the mechanistic view of science” (Machamer, Darden and Craver 2000). This view holds that science doesn’t formulate laws or pick out causes, but mainly describes mechanisms – and its proponents make explicit in their papers what this rough characterization involves. Mechanisms are supposed to only involve specific “entities” with specific “activities”, all of which being sufficient to account for the way mechanism does function and yields as its outcome the phenomena to be explained. Interestingly, the main application of this conception has been about biological sciences, e.g. molecular biology (Darden, 2006) and neurosciences (Craver, 2008). Philosophers debate about whether it correctly captures the metaphysics of science, or only captures the activities of scientists. Yet, since this approach views the objects of science as mechanisms made of entities with activities, and those mechanisms function, one could suggest that those activities are the functions of the entities. Hence the mechanistic view of science raises conceptual issues about the meaning of function, and the role of functional explanations in the depiction and uncovering of those mechanisms.

  • B. In the cognitive sciences, new developments such as “situated cognition” or “embedded cognition” (e.g. Shapiro 2010), challenging the classical cognitive and connectionist viewpoints, offer new insights on what it means to have a function. Such is the case with the refined analyses of explanations in neurology and in cognitive sciences that have been produced recently by various philosophers (e.g. Bechtel and Richardson, 1993; Bechtel & Abramsen, 2005; Craver, 2001), often in connection with the “mechanistic” philosophy of science just mentioned. In many cases, the notion of function relies upon some understanding of the mechanisms at stake in the cognitive devices and which scientists intend to grasp. This could be taken in favor of the simplest causal role theory of functions; however given that the very meaning of “mechanism” has been re-worked; the consequences of these analyses are not so clear cut. A new understanding of what mechanism should mean in the field would therefore impinge on what functions are and what they do explain.

C. In biology:

    • C1. All etiological accounts of function share a general appeal to natural selection in order to make sense of the explanatory force of functional statements. However, what selection is and how it is ascribed is often not detailed in these accounts. For instance, Wright (1973) was very general and equated selection and choice as two modes of the same selection process; Millikan (1984) had a very idiosyncratic redefinition of selection; etc. Philosophers of biology sometimes saw the importance of being clear about what selection is for the function issue, as exemplified by the use of Sober’s selection for/selection of difference in this context (Enc and Adams, *). But precisely, in the last decade, many issues have been raised about natural selection. Some may be too metaphysical to really impinge onto the function debate (e.g., whether selection is a cause or a statistical outcome (Walsh et al., 2001; Matthen and Ariew 2009; Lewens, 2009; Huneman 2011); or what selection actually causes (e.g. Sober, *; Neander, *)). But some issues may be more directly relevant to biologists and therefore have consequences upon what functional ascriptions and explanations are.

    • C 1. Lewontin (1971) had shown that any set of entities exhibiting variation over heritable properties causally related to differential reproduction (fitness) seemed to be potentially undergoing natural selection – and these seemingly necessary and sufficient conditions for natural selection were accepted for a long time by philosophers. Yet Godfrey-Smith (2009) has shown that natural selection is not easily captured in terms of necessary and sufficient conditions. Especially, there is a philosophical debate about whether heritability really is needed to define natural selection, or not. Evolution by natural selection needs inheritance, according to Brandon (2009), but not natural selection itself. Additionally, the whole idea of fitness came unto scrutiny recently (Abrams, *; Bouchard, *, who challenged the whole frame of evolutionary population genetics.) Moreover, recently we saw the development of a multi-level selection paradigm for explanations of issues like cooperation (Damuth and Heisler, 1987; Sober and Sloan Wilson, 1998), evolutionary transitions towards individuality (Michod, 1999; Okasha, 2006; Griesemer, 2000), or genomic conflict (Burt and Trivers, 2006). Given that the etiological theory of function defines function by an appeal to selection, it will be now crucial for philosophers to confront multilevel selection in their conceptions of “selected effects” function, where implicitly selection was usually assumed to operate at the level either of the gene or of the organism (Huneman, forth.).

    • C2. There is a growing discussion about the need to “extend” the classical evolutionary tehory (e.g. Pigliucci, 2007), stemmed from the synthesis of Mendelian genetics and Darwinian transformism, essentially using population genetics models as the ones designed by Fisher, Wright and Haldane in the 1930s. From this viewpoint, the scope of selection may not be globally encompassing, especially, the variations upon which selection acts may have been more sophisticated than mere allelic mutations and recombination. In this view, the mechanisms producing variation, in a regular and systematic way, have thereby a crucial role in evolution, or at least macro evolution. Structuralists like Goodwin or Hall had for a long time argued that the important features in evolutionary long-run history, and especially the commonalities of some forms and process across very distant phyla, may not been explainable by selection (e.g. Amundson 2005, for a short historical sketch). Current developmentalists (e.g. Raff, *; Shubin, *; Gilbert, *, etc.) are not always undermining selection in such a hard way but clearly they advocate the role of other processes - acting within the stage of variation, and often at the level of organisms rather than genes - in the shaping of living traits. If the role of selection in evolution regarding the explanation of diversity and even adaptation is to be reconceived, an account of functions based on natural selection, such as the etiological account, may become less accurate or at least less systematically valid for biology. It might mean a reinforcement of the causal-role tehory; but it may also claim for more distinct reconception of what are functional traits, functions of behaviors, etc. - a reconception likely to include development and organismal activity within the account.

    • C3. Besides, ecology and evolution entered a new relationship. It has often been claimed that the Modern Synthesis left ecology aside (e.g. Kingsland 1989), because it was centered on population genetics, which mainly targets one population of one species, whereas ecology considers sets of population of several species. Recently, we witness various attempts to synthesize ecology and evolution, be it in the context of niche-construction theory (Odling-Smee, Laland and Feldman, 2003), in a reconception of the basics of ecology (Ginzburg and Colyvan, 2004), or in the rise of metacommunity ecology (Leibold et al. 2004), especially in the form of the neutral theory of ecology (Hubbell 2001). Thereby, it makes it all the more important to understand functional explanations in ecological contexts, whereas the bulk of philosophical work has been centered on evolution.

  • In metaphysics, functionalism has always been defined with a reference to multiple realizations (e.g. Putnam, 1967; Fodor, 1974). This constitutes an important background for what philosophers meant by talking of functions. Especially, functional properties were conceived of as a relation between a type of input and a type of output, the nature of what played the role of this relation being somehow irrelevant, and possibly infinite; this is the famous hyperbole by Putnam, saying that even a chunk of Swiss cheese could think if it were exhibiting the appropriate functional correspondences.

Yet recently, coming from the philosophy of mind, attention has been paid to what “realization” exactly means (Shapiro, 2000; Polger, 2004, 2007; Gillett, 2003), and philosophers emphasized difficult issues implicit in the very meaning of “realization” itself. This implies that, if philosophers still think of functions in terms of realization – for example when they say that the same functional properties are realized by various possible processes – they will have to make precise the metaphysical stance they adopt. Some of the stances, for example, are not entailing Putnam’s weird Swiss cheese consequence, because they restrict the ontological class of potential role-occupiers (e.g.Block, *). That is the reason why the way one handles such issues about “realization” bears important consequences upon the very idea of function implied by functionalism, and finally on the concept of “function” in general. Granted, the “function” of functionalist philosophers of mind is not the “function” of behavioral ecologists, captured by philosophers who support the etiological theory of functions; however, as it is attested by the example o functions like seeing or storing or transmitting information, they are sometimes intended to capture the same core fact1. Therefore the original issues about functionalism and functions in mind are not irrelevant to a general questioning upon functions and the compared value of etiological and causal role accounts.
Thus, both philosophy of science, cognitive and neuroscience, recent debates in evolutionary biology and ecology, and the metaphysics of realization involve important consequences about the concept of function and functional explanation, which must in the end affect the traditional theories of function, even in their most sophisticated form. The papers edited here intend to meet the challenge that this new scientific and philosophical context raises. They present and discuss issues on functions and functional explanations that have arisen recently, although not all the challenges listed here will be addressed.

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