Physiological Function, Health and Medical Theory

Transcription

1 Physiological Function, Health and Medical Theory Amanda Thorell PhD-student at the Department of Philosophy, Stockholm University Abstract In medicine, the concepts of normality, abnormality, health, and pathology are frequently used. Another frequently used concept is that of physiological function, which the previously mentioned concepts are usually taken to involve or apply to. A comprehensive naturalistic theory of biological normality/abnormality or health/pathology reasonably comprises some account of physiological function. The most well known theory of health/pathology, which includes an account of normality/abnormality, is perhaps Christopher Boorse s biostatistical theory (e.g. 1977). In this theory, physiological function ascriptions are made in accordance with a goal-analysis: the function of a trait is determined by its contribution to the organism s physiological goals, which are specified as individual survival and reproduction. This paper aims to defend this analysis of physiological function. In doing this, I make two important distinctions: first, a distinction between two types of function ascriptions made in medical theory, and, second, a distinction between efficient functioning and health. Daniel Hausman argues in Health, Naturalism, and Functional Efficiency (2012) that Boorse s analysis is too narrow. There are, he claims, functions within subsystems within organisms, which contribute to the goal of the subsystem, yet undercut the goal of the organism. These are excluded by Boorse s goal-analysis. One example Hausman uses to show this is about a malignant tumor. The blood vessels in a malignant tumor, Hausman says, have the function of providing the cells of the tumor with oxygen and nutrients. Boorse s analysis, however, does not ascribe the blood vessels in the tumor this function, since they do not contribute to the goal of the organism. Rather, by supplying the cells of the tumor with oxygen and nutrients they are detrimental to the organism. In order to solve this problem Hausman suggests to widen Boorse s analysis, so that the goals referred to need not be those of the organism, but any organic system. I agree with Hausman that the blood vessels in a malignant tumor have the function of supplying the tumor with nutrients and oxygen, and that Boorse s analysis of physiological function cannot account for that. However, I disagree with Hausman s proposed solution. Considering medical theory, I argue that Hausman s amendment is unsound. I advise to instead solve the problem by distinguishing two types of functions that play different roles in medical theory, namely physiological functions and causal role functions. According to this suggestion, the blood vessels in the tumor have no physiological function. However, they have a causal role function. Answering a second example that Hausman brings up, I make a further important distinction, namely between efficient functioning and health. Although all healthy functions are (relatively) efficient functions, not all efficient functions are healthy. This is because all physiological functions cannot be ascribed health or pathology. The concepts of health and pathology only apply to function tokens that are of a type that is typical within a reference class.

2 1. Introduction In medicine, the concepts of normality, abnormality, health, and pathology are frequently used. So is the concept of physiological function, which the previous concepts are usually taken to involve or apply to. A comprehensive naturalistic theory of biological normality/abnormality or health/pathology reasonably comprises some account of physiological function. The perhaps most well-known theory of health/pathology, which includes an account of normality/abnormality, is Christopher Boorse s biostatistical theory (e.g. 1977). In this theory, physiological function ascriptions are made in accordance with a goal-analysis: the function of a trait is determined by its contribution to the organism s physiological goals, which are specified as individual survival and reproduction. In Health, Naturalism, and Functional Efficiency Daniel Hausman (2012), although to a large extent agreeing with Boorse, discusses a couple of issues with the biostatistical theory. Of these, one specifically concerns the analysis of physiological function. Hausman argues that Boorse s analysis is too narrow, and suggests an adjustment of it to solve the problem posed. Although I think Hausman notices something important in his argument that Boorse s analysis is too narrow, I disagree with his suggested solution. This paper aims to show how the problem Hausman brings up can be more adequately handled, without amending the goalanalysis of physiological function. The paper proceeds as follows: Section 2 presents Boorse s account of physiological function and how it is incorporated in the biostatistical theory. Section 3 presents Hausman s problem. Section 4 discusses how to deal with it. Section 5 concludes. 2. Boorse s Account of Physiological Function and the Biostatistical Theory Christopher Boorse provides an account of physiological function as part of his biostatistical theory (hereafter, the BST ). The aim of the BST is to provide an explicative analysis of the physiologist s/pathologist s theoretical concept of disease or pathology (Boorse 2014, 713). Boorse distinguishes this theoretical concept from other possible disease concepts (e.g. clinical, social, political) (1997, 11). An important point about the BST is that it is value-free; it has no normative component parts and no normative implications by itself. What Boorse accounts for is health and pathology as naturalistic biological phenomena, being the same for animals and plants as for humans. The account of physiological function in the BST is a goal-analysis (Boorse 1976, 1977, 2002). It is a specification of the following general goal-analysis (Boorse 1976, 80): X is performing the function Z in the G-ing of S at t, means At [time interval] t, X is Z-ing and the Z-ing of X is making a causal contribution to the goal G of the goal-directed system S. This analysis, Boorse points out, is context dependent. What serve as goals and systems depend on the context in which the function claim is made. However, if we look at biology we find goal-directedness, or teleology 1, at many levels of organization (Boorse 1976, 82-83). Boorse writes: 1 The notion of teleology here is not intentional or Aristotelian.

3 Individual cells are goal-directed to manufacturing certain compounds; thereby they are contributing to higher-level goals as muscle contraction; these goals contribute to overt behavior like web-spinning, nest-building, or prey-catching; overt behavior contributes to such goals as individual and species survival and reproduction. (1977, 556) The systems and goals relevant for function claims, Boorse explains, are those at the apex of the hierarchy of systems and goals. Where this apex is to be found depend on the interest of the biological subfield in which the claim is made. Since Boorse s interest is in physiology/pathology, the question is what systems and goals these disciplines are concerned with. The relevant systems, or teleological units, he claims, are individual organisms, and the goals of these are their own survival and reproduction (1976, 84). Applied to physiology the account hence becomes: The part/process X is performing the physiological function Z in the attainment of survival or reproduction of the organism S at t, means At t, the part/process X is Z-ing and the Z-ing of X is making a causal contribution to the survival or reproduction of organism S. For example: Anna s heart is performing the function of circulating blood in the attainment of survival or reproduction of Anna at the 19 th of July 2017, means: At the 19 th of July 2017, Anna s heart is circulating blood and the circulation of blood is making a causal contribution to the survival or reproduction of Anna. This account of physiological function is then incorporated in Boorse s account of disease, expressed by the following four clauses (1977, 562): (1) The reference class is a natural class of organisms of uniform functional design; specifically, an age group of a sex of a species. (2) A normal function of a part or process within members of the reference class is a statistically typical contribution by it to their individual survival and reproduction. (3) Health in a member of the reference class is normal functional ability: the readiness of each internal part to perform all its normal functions on typical occasions with at least typical efficiency. (4) A disease is a type of internal state which impairs health, i.e., reduces one or more functional abilities below typical efficiency. It should be noted with regard to clause 2 that the and in survival and reproduction should be understood as an inclusive or (Boorse 2014, 685). In the following, in that context, I will use or with the inclusive meaning in mind. 2 In the above account we can see that two things Boorse draws on to account for normality, health, and disease are, first, typicality of function types, and, second, typicality of efficiency levels of typical function types. A normal function is a function (i) whose type is typical within the reference class and (ii) whose contribution to the physiological goals lies within the range of typical efficiency levels. A healthy organism is an individual whose part-functions 2 I leave the question aside of how these two goals are to be handled in relation to each other.

4 all fulfill (i) and (ii), or alternatively to (ii) have a level of contribution to the physiological goals that is abnormally high. A diseased organism is an individual who has some partfunction that fulfill (i), and whose level of contribution to the physiological goals is abnormally low. 3. Hausman s Problem Daniel Hausman (2012) argues that Boorse s analysis of physiological function is too narrow. First, he claims, there are functions within subsystems within organisms, which contribute to the goal of the subsystem, yet undercut the goal of the organism. These are excluded by Boorse s goal-analysis. Hausman uses an example of blood vessels within tumors to illustrate his point: The blood vessels in a lipoma (a benign soft-tissue tumor) have the function of providing oxygen and nutrients to the cells of the lipoma and removing wastes, even though the lipoma has no function. The same can be said of the blood vessels in a malignant tumor, even though this functioning diminishes the functioning of other systems and shortens the organism s life. (2012, 521) Second, Hausman shows that there may be cases where a certain condition is in one respect beneficial for the organism, but is at the same time detrimental to some of its subsystems. The example Hausman makes here is about the skin condition pinta. This condition is caused by a certain bacterial infection causing lesions and thereafter discoloration of the skin. Hausman writes that in some tribes, in which the condition is common, the discoloration is viewed as attractive and not recognized as a disease because of its high prevalence and purported aesthetic value. 3 Hausman thinks that there is a problem here, because if the condition enhances reproductive success in the environment of the tribe, lacking the discoloration would be pathological, although the condition is pathological with regard to the goals of the skin, e.g. the goal of sealing out contaminants (2012, ). The point Hausman seems to be after is that we get a contradiction with Boorse s analysis, since we cannot say that pinta is healthy and pathological at the same time. Boorse s analysis cannot ascribe physiological functions in relation to the skin in opposition to the organism. To account for these cases, Hausman suggests to remove the restriction of goals to that of the organism s survival or reproduction. He proposes the following account of the comparative functional efficiency of two sets of capacities C and C of a part within some organic system S with goal G : On the assumption that the other parts of the organism or systems whose activities do not depend on C or C are functioning adequately in a relevant environment, The functional efficiency of C is greater than that of C in some system S with respect to some goal G if and only if C makes it more likely that S achieves G than does C. (2012, 534) 3 The term discoloration is a bit unfortunate here, since members of the tribe would not describe the affected skin as discolored.

5 This account is more unrestricted than Boorse s, most clearly in that it relates physiological functions to the goals of any organic system, instead of merely whole organisms, but also in that it allows for (some) further goals than individual survival or reproduction. In this paper the discussion will be confined to the first aspect, about which systems are relevant. Hausman writes that goal achievement in organic systems (non-whole-organisms) typically contribute also to the goals of the organism, but when that is not the case the above account makes it possible for us to adopt different perspectives, although the [f]unctional efficiency within the organism is usually of more interest and importance (2012, 535). 4. Discussion of Hausman s Problem In this section I will make two arguments, one for each of Hausman s examples. The first (4.1.) concerns the role of the concept of physiological function in medical theory. The second (4.2.) concerns the relation between physiological functions and health/pathology The tumor case I think Hausman is correct about there being a sense in which the blood vessels in a tumor have a function. Since we cannot say that they have a physiological function on Boorse s account, this may seem to be a counter-example to his analysis. 4 Blood vessels in tumors certainly play some crucial role in the cancer process; erasing facts about their function of supplying the tumor with nutrients and oxygen in an oncology book would clearly count as erasing important knowledge, which may for example be important if we want to obstruct the cancer process. However, in some contexts it seems reasonable to say that the blood vessels in a tumor have no function, because they do not fill a function for the organism carrying the tumor. This dissonance between intuitions saying that the blood vessels in the tumor have a function and that they do not is what Hausman captures when he talks about adopting different perspectives: we can set the focus on the tumor, or we can set the focus on the organism. That Hausman s account allows us to do so may be seen as a virtue. However, I think the way in which Hausman s account enables us to do this is not sound. As we saw, Boorse s goal-analysis, specified as an analysis of physiological function, limits the possible systems to organisms with the motivation that they are the teleological units in physiology/pathology; it is the goals of them that stand at the apex in the goal-hierarchy in these disciplines. This seems to me a very feasible claim. Was it not for the interest in organisms functioning and health, pathologists would not care about the function of blood vessels in tumors. But patently, acknowledging functions of the blood vessels in tumors reveals function claims in pathology where organisms are not the systems referred to. However, in order to solve the problem I think we should not give up on the restriction of organisms as teleological units in physiology/pathology. Rather, we should take seriously the difference between having a function in the sense that for example the blood vessels have in a 4 One way to try to solve the tumor case, which I will not embrace, would be to try to argue that (malignant) tumors are not part of the organism in which they reside, but are rather organisms by themself. (This is e.g. Lauren Seiler s (2007) view.) Then we could say that the blood vessels in the tumor have a function by contributing to the goals of the tumor. However, even if we acknowledged tumors as organisms there are still other kinds of tissues developing in human beings that are less plausible candidates of being organisms, which could instead be used to make Hausman s point.

6 healthy body and having a function in the sense that the blood vessels have in tumors. Accordingly we should distinguish between two types of functions that play different roles in medical theory. The suggestion is to keep Boorse s goal-analysis of physiological function, but complement it with a causal role analysis for non-physiological functions. Let Boorse s analysis describe functions that contribute to the organism s physiological goals, i.e. physiological functions. Let the causal role analysis describe functions that occur in a physiological body, yet are not contributing to any goal of the organism. These functions need not be detrimental to the organism; they may be neutral in this regard. For the causal role analysis I rely on Robert Cummins account: the (or a) function of x in a system Σ is f relative to a capacity C of Σ just in case Σ s capacity to C analyzes (in part) into x s capacity to f. (1996, 116) It can be noted that this analysis is very similar to Boorse s general goal-analysis, where goals and systems are unspecified. It might come down to a matter of taste which of these two analyses to use for non-physiological functions. However, I choose the causal role analysis in order to more clearly contrast physiological function ascriptions from other function ascriptions in medicine. This enables us to say that whereas the blood vessels in a healthy body contribute to a goal (of the organism), the blood vessels in tumors merely contribute to an effect of cancer (e.g. tumor growth). Of course, all physiological functions will, in addition to being goal-related functions, be possible to analyze as causal role functions. However, my point is that we for methodological reasons should describe these in accordance with the more demanding goal-analysis, rather than with the causal role analysis. In our understanding and prediction of, and pursuit of health in, the human body the goal-analysis and the causal role analysis play different, but individually crucial, roles. Physiological functions explain how we succeed in living, and an analysis of these functions enables us to make a distinction between health and pathology. Causal role functions, on the other hand, just explain how things work. By the goal-analysis we find out whether there is pathology (in virtue of reduced efficiency), but in order to understand why the efficiency is reduced we need the causal role analysis The pinta case Let us now look at Hausman s second example, about the skin condition pinta, being detrimental to the skin s function of sealing out contaminants but enhancing chances of attracting a partner. This case, I will argue, fails for a different reason to motivate Hausman s liberal view on what can serve as systems in the account of physiological function. First, however, I will set aside one complicating aspect of the example. There is not only an issue about systems in Hausman s example, but also a problem of how to treat the two goals of survival and reproduction in relation to each other. While attracting a partner is only relevant for the goal of reproduction, sealing out contaminants is firsthand relevant for survival, but indirectly also for reproduction. To set aside the problem of how the goals are related, I will only consider the skin s function of sealing out contaminants as a contribution to reproduction. The case is then that pinta makes the skin in one respect less beneficial, and in another respect, in a certain environment, more beneficial, for reproduction. Hence, we

7 have a case where a pathological condition becomes physiologically advantageous in a certain environment. Do we need to, as Hausman claims, relate to different systems to account for this case, and accordingly say that pinta is pathological for the skin but healthy for the organism? No, we need not. First, let us note that there is no problem by itself in ascribing a lowered efficiency of the skin in case of pinta by referring only to the goal of the organism (and not of the skin). Pinta is simply detrimental to the organism by being detrimental to the skin. However, in Hausman s example there is a conflict: pinta is in one aspect detrimental, and in another aspect beneficial, for reproduction. But the important thing here is to distinguish the questions whether something has a function and whether it is healthy. When a trait contributes to the organism s reproduction it has a physiological function. The discolored skin of a tribe member hence has the physiological function of attracting mates. But for a trait to be healthy or pathological (according to the BST) it must furthermore be a physiological function of a certain kind, namely a reference class typical function. In the example, Hausman mistakenly describes the lack of pinta as pathological (among the tribe members). But lacking this condition is no pathology, since the function of the discolored skin to attract mates is a not a reference class typical function. It is a function which arises in a special environment. Hence, in the example, pinta has a physiological function (attracting mates), and it is a skin disease (by lowering the efficiency with which the skin contributes to the organism s reproduction). 5 However, if pinta was common and enhanced chances of reproducing for most members of our species, would we not at least then face a problem? It might seem as if pinta would then be both healthy and pathological for the organism. But this, I will argue, is not how we should understand such a case. For a given species, we will find a lot of functional compromises, i.e. traits with several functions where the efficiency level of one function is lowered in favor of the increased efficiency of another. This does not imply that there is some pathological condition. As an example, think of the larynx. The larynx both has the function of protecting the trachea and lungs against food aspiration and the function of producing sounds. Even if the larynx s function of producing sounds lowers its efficiency level with regard to avoiding aspiration (since talking while eating increases risk of aspiration), this does not mean that a larynx is pathological by producing sounds. On the whole, the larynx s function to produce sounds makes the possessor more likely to succeed in her physiological goals than what would be the case if it would not have that function. Hence, if pinta was common and enhanced the chances of reproducing to such an extent that it on the whole made possessors more likely to succeed in reproduction than non-possessors, pinta would not be a skin disease. 5. Conclusion Hausman is correct that Boorse s goal-analysis of physiological function cannot account for all function ascriptions made in medical theory. However, the way to go, in order to account for all functions we may want to ascribe, is not to amend the analysis of physiological function. Rather, we should acknowledge a distinction between physiological, goal-related, 5 This answer to Hausman is in line with Boorse (1997, 87-88), where he responds to objections of similar kind.

8 functions and causal role functions, and also a distinction between efficient functioning and health. References Boorse, Christopher Wright on Functions. Philosophical Review, 85: Health as a Theoretical Concept. Philosophy of Science, 44: A Rebuttal on Health. In What is Disease?, ed. James M. Humber, and Robert F. Almeder, Totowa, NJ: Humana Press A Rebuttal on Functions. In Functions: New Essays in the Philosophy of Psychology and Biology, ed. André Ariew, and Robert Cummins, Mark Perlman, Oxford University Press A Second Rebuttal on Health. Journal of Medicine and Philosophy, 39: Cummins, Robert Representations, Targets, and Attitudes. Cambridge, Mass.: MIT Press. Hausman, Daniel M Health, Naturalism, and Functional Efficiency. Philosophy of Science, 79: Seiler, Lauren H What Are We? The Social Construction of the Human Biological Self. Journal for the Theory of Social Behaviour, 37 (3):