Abstract
In the debate about the concepts of disease and health, recent contributions have pointed to a potential shift in emphasis. It has been suggested that the biostatistical theory (BST) of disease, proposed and defended by Christopher Boorse at intervals over the last 30 years (Boorse, 1977, 1987, 1997), should no longer receive the attention that it has so far attracted (Khushf, 2007). Since such a great deal of this attention has been concerned with criticizing the BST, it now appears to be time that it was left behind altogether as we move forward into a new phase in the debate. Khushf (2007) has suggested that Lennart Nordenfelt's theory of health now provides the primary theory in the field and this should now be the theory that receives the greater share of critical attention.
However, while this may appear to be a reasonable course of action, there are noticeable differences between the perspectives adopted by Nordenfelt and Boorse – so much so that it was Nordenfelt himself who appears to have been the first to have described his and Boorse's positions as representing two different schools of thought (Nordenfelt, 1986). Whether these schools were ever meant to be mutually exclusive is a moot point. The two schools certainly viewed the human being (and being human) differently. While these schools may have been at odds, their coexistence was all the more intellectually stimulating for it.
Re-focusing attention onto just one approach may, therefore, result in an ensuing intellectual inbalance. This paper will suggest that what is needed is a continued balance between the humanistic and biological perspectives. If the BST is to be sidelined an alternative physical model underpinning the notions of disease and health is needed in its stead.
Since the BST was first proposed, there have been changes in the biological view of disease; the field of evolutionary (or Darwinian) medicine has emerged and the human genome has been sequenced. The simple interpretation of disease as essentially 'bad' and the simple cause-effect explanations in genetics are now problematic. There is a need to understand disease in an evolutionary context and in terms of multi-disciplinary systems biology.
Within the context of these developments, this paper will propose that a unitary approach to understanding the concepts of disease and health is neither necessary nor desirable and will consider what the characteristics of a biologically-orientated complement to the humanistic approach to understanding these concepts should be.
Although important to medicine, the concepts of disease and health have, for a long time, been philosophically problematic and we continue to be without definitions that all find acceptable. Indeed, the more closely one investigates these terms, the more problematic they seem to become and the further we seem to be from a resolution.
While our inability to provide definitions for disease and health has, in fact, a long history, the nature of the present debate about these terms has its roots in the 1970s with the work of Christopher Boorse who, at intervals over the intervening period, has propounded a theory of disease now known as the biostatistical theory (or BST). Briefly, this theory suggests that disease and health can be understood in statistical terms; that somebody for whom physiological part-function is at the lower limits of the typical range is, as a result, classifiable as having a disease. As a corollary, those who do not fit into this category can be considered as healthy; here, the notion that health is the absence of disease is deemed acceptable.
Two important aspects of the biostatistical theory are worth pointing out. Firstly, a theory that speaks in statistical terms such as these is at once attractive to those engaged in biomedical science who, as I shall go on to note, typically take a statistical approach to their work. While this can include those active at the 'sharp end' of clinical practice, it is perhaps particularly characteristic of those who give support to that work as well as those whose interest is more academic. Here, one is specifically thinking of those engaged in teaching and research in – what has come to be called – 'Health Science'. For such as these, a scientific (or, at least, a scientific–sounding) theory is not only attractive but arguably essential. For there to be a subject that can be called 'Health Science' at all, the notions of health – or, more often in practice, the notions of disease – need some logical or objectively rational basis for the subject to warrant the title 'science'.
The second striking feature about the biostatistical theory is that, since it was proposed, a great deal of the attention it has received has been aimed at criticizing it. Khushf (2007) notes that in his famous defence of the biostatistical theory – his rebuttal of 1995 – Boorse himself lists over 100 citations that find fault with his views. Indeed, in the light of this, Tengland (2007) considers the biostatistical theory to have been 'thoroughly refuted over and over again'.
Indeed, in the debate about the concepts of disease and health, recent contributions have pointed towards a potential shift in emphasis. Khushf (2007) has suggested that the biostatistical theory should be left behind and that we move forward into a new phase in the debate. In so doing, he has also suggested that Lennart Nordenfelt's theory of health now provides the primary theory in the field and it is this which should now receive the greater share of critical attention.
In brief, Nordenfelt comes to a conception of health from a position in action theory and defines health in terms of the ability of an individual to achieve certain (what he calls) 'vital goals'. Thus, there is a substantive difference in the nature of the theories proposed by Boorse and by Nordenfelt. While Boorse speaks statistically in terms of 'part–function', Nordenfelt speaks of the individual in terms of what he or she can achieve. Indeed, the differences between Boorse and Nordenfelt are such that it was Nordenfelt himself who appears to have been the first to have described his and Boorse's positions as representing two different schools of thought (Nordenfelt, 1986).
While, in some respects, these two schools of thought may have been at odds, there was also a sense in which their coexistence was complementary. That is not to say that our picture of disease and health was made complete by some sort of synthesis of these two perspectives but it was, arguably, fuller and, perhaps, more stimulating for the presence of both.
Indeed, whether the two schools of thought represented by Boorse and by Nordenfelt's ideas were ever meant to be – or could ever have been – mutually exclusive is a moot point. The two schools viewed the human being (and for that matter being human) from quite different perspectives. The biostatistical theory emphasized function – particularly at an impersonal physiological level – whereas Nordenfelt emphasized abilities expressed by persons.
However, while the marginalization (if not abandonment) of the biostatistical theory may appear to be a reasonable course of action given the criticism and lack of acceptance it has experienced, a world without the biostatistical theory – or at least its successor – would be one within which there would be something of a part–vacuum.
If the re–focusing of attention onto Nordenfelt's ideas, that Khushf (2007) suggests, means that just one of the previous two schools of thought continues to attract attention and the other perspective is lost, then this may result in a conceptual imbalance. An exclusively humanistic emphasis on a person's vital goals – valid though this might be – may, at the same time, detract from finding explanations in terms of the biological bases of our existence.
While not wanting to sound like a biological determinist, neither do I want us to lose sight of the fact that we are all biological beings and that our physically embodied, biological nature can have a direct bearing upon our well-being at all levels and that this aspect of our being must be taken into account.
I want to suggest then that what is needed is not victory for one or other school of thought over its supposed rival but rather that a balance between the perspectives they seek to explore – those I have described as humanistic and biological – needs to be struck.
Thus, if Nordenfelt's ideas are to provide the primary theory in the field – and I have no objection to this – it should not provide the only theory; if the biostatistical theory is to be sidelined, an alternative theory describing the physical, biological nature of our experience of disease and health is needed in its stead. While I have made some attempts to that end, I do not intend using this forum as a means of self-promotion (and certainly not as presenting myself as Christopher Boorse's successor). Instead, what I want to consider in the remainder of this paper is what I think any model that does replace Boorse's biostatistical theory should try to include.
Key here is something that is conspicuously absent from our current biological accounts of disease and health and that is a focus on the individual as a single, whole organism rather than on the functioning of parts. An image I like to give as a metaphor for our overly reductionist approach to the biological aspects of disease and health is that of Humpty Dumpty. We are adept at taking him apart to see what is supposedly going 'wrong' but we cannot put him back together again – at least, not in a conceptual sense: we lack a thoroughly worked-out theory of the organism as a single unified biological entity. This, I think, is a serious short-coming, not only in terms of our understanding of disease and health but also in scientific terms.
Yet, it is the organism as an entity – as a person – with which the humanistic approach feels it needs to begin. Why is this not also the case for the biological approach? Why, when dealing with illness, disease and health, should personal experiences not be considered to be valid biological phenomena worthy of investigation and interpretation? The approach adopted by the biostatistical theory is typically that adopted by biological science as it has prevailed so far in that it takes a depersonalized statistical, rather than a personalized individual, approach to defining disease and health; it looks to what can be derived from averaging the population rather than from what can be derived from a focus on the individual. Except perhaps in palaeontology where there may on occasion be only a single specimen available for study, the biological sciences do not make generalizations based upon individual cases. That is not to say that reasonable generalizations are not possible or, therefore, that the present situation cannot change.
Since the biostatistical theory was first proposed, there have been changes in our understanding of the biological processes associated with disease and health. Indeed, during this time, disease has changed from being of primarily clinical interest to something that now increasingly interests others. It is no longer the preserve of the medical and related professions and the medical touchstone of the alleviation of suffering does not necessarily form the basis upon which others seek to understand disease. For example, physical anthropologists – as distinct from cultural and medical anthropologists – now have their own particular interest in disease. With the emergence of the field of evolutionary (or Darwinian) medicine, departments of anthropology – particularly in the US but also in the UK – have come to view differences in disease incidence and expression in more than simply epidemiological terms. It is not some reified thing called 'disease' that indiscriminately takes hold of unsuspecting individuals; there are differences between individuals in terms of their susceptibility to different conditions and it is these individual differences that need to be understood. These differences in susceptibility reflect, in turn, the underlying differences that exist in the genetic constitution of the individual and which, therefore, interest the modern physical anthropologist.
Also, any simplistic interpretation of disease as something essentially 'bad' has come to be seen as problematic. To use something of a now 'classic' example, we know that sickle cell trait, while a cause of marked suffering for the individual, also confers on that individual a defence against malaria. It may be argued that, on balance, the overall advantage in terms of survival that sickle cell trait offers outweighs the suffering experienced.
Instead of being 'disease–centred' we need a biological theory of disease and of health that is individual (or organism) centred – one that also accounts for the positive aspects of suffering. It is the individual with a given condition – or who has a certain biological state – that needs to be understood in context not just the mere mechanics of pathophysiological processes in isolation.
(I should add in passing that arguments similar to those proposed for the 'classic' example of sickle cell trait have also been proposed for other conditions including various forms of thalassaemia and also cystic fibrosis. In each case, debilitating conditions that frequently elicit medical attention appear to be offering defences against other conditions.)
The epidemiological character of the biostatistical theory does not describe the individual organism adequately enough. It is only in and through the individual organism that disease – and for that matter health – exists. However, as I have been emphasizing, we do not, as yet, have a fully worked-out theory of the organism. For example, now that the human genome has been sequenced, one of the most striking findings is that we are made by far fewer genes than was previously thought. The consequences of this are quite dramatic but many seem to have missed their significance. The simple cause–effect explanations in genetics – although not entirely wrong – are now problematic in that they clearly do not describe adequately what must be going on. If there are fewer genes than earlier theories of morphogenesis proposed, a much greater complexity in the way the genome operates in producing and maintaining an organism appears to be the case. Although the idea of 'a gene for something' sometimes works, there are serious problems in how far this notion can be extrapolated. Instead, it appears that more holistic notions of 'genetic constitution' consisting of sets of interacting genes now need to be developed.
While there have been those I have mentioned who have provided what they see as philosophical reasons why the biostatistical theory should be side–lined, there are biological reasons as well – such as those I have just touched upon. Certainly, the biology upon which the biostatistical theory is based has moved on and continues to do so – with much still to be uncovered.
Here I should mention two particular areas of research that are likely to be of potential relevance: these are systems biology and complexity theory. Any 'theory of the organism' that is developed in the future is likely to be informed by ideas that are emerging from these areas of study.
The point I want to emphasize though is, I think, clear: as new ways of understanding the organism have begun to emerge since Boorse first proposed the biostatistical theory, these must not only be accommodated by the biostatistical theory's successor, they must also be built into a new biology of the individual. Such a biology, distinct from our present statistical biology, is one that would also accommodate disease and health as different states of the organism rather than differences in the function of various parts.
So, by way of conclusion, let me refer directly to my title. When I speak of 'a new biologically–orientated concept of disease and health', I am not suggesting that our concept (or concepts) of disease or health should be biology–only or only–biology. There is scope, I believe, for different schools of thought to coexist; they need not be mutually exclusive – after all there is no single understanding of human beings. Instead, there may be potential for overlap of ideas – perhaps even cross-fertilization. What I hope I have highlighted is that for biology to be missing from our set of perspectives would be to our detriment. If we are to lose the main biologically–based theory of disease and health currently available, we must replace it so as to fill the void that would otherwise ensue. In that way, the stimulating effects of having different schools of thought about disease and health noted earlier would continue to be the case.
References:
Boorse, C. (1977). Health as a theoretical concept. Philosophy of Science, 44, 542-573.
Boorse, C. (1987). Concepts of health. In D. Van De Veer & T. Regan (Eds.), Health Care Ethics: An Introduction (pp. 359-393). Philadelphia: Temple University Press.
Boorse, C. (1997). A Rebuttal on Health. In J. Humber & K. Almeder (Eds.), What is Disease? Totowa, New Jersey: Humana Press.
Khushf, G. (2007). An agenda for future debate on concepts of health and disease. Medicine, Health Care and Philosophy, 10(1), 19-27.
Nordenfelt, L. (1986). Health and disease: two philosophical perspectives. Journal of Epidemiology and Community Health, 41, 281- 284.
Acknowledgements:
I would like to thank the trustees and fellows of the Konrad Lorenz Institute, Altenberg, Austria, where, as a Visiting Fellow, I was able to develop the ideas expressed here. I would also like to thank Annette Lewis for her help in the preparation of this transcript.