On the Place of Disease and Health in Human Existence

In the UK, in recent years, there has been a considerable expansion in higher education. As part of this, there has been an increase in the number of courses that relate in some way to health with the result that courses in 'Health Science' – which tend to be associated with departments of biological science – and 'Health Studies' – which tend to be associated with departments of social science – have become very popular. There is now a considerable interest in 'health' as an academic discipline from those who do not want to go into any of the clinical or paramedical professions. There are now those who want a serious, informed and often specifically scientific understanding of health-related matters. A distinctively non-professional, non-vocational interest in health is now developing.

Exactly why there should be such an interest is unclear. A number of suggestions might be made but the implications of this trend are, perhaps, more pertinent. It means that problems in the understanding and interpretation of health-related concepts that were once confined to medicine now have a wider audience. Certain problems in the philosophy of medicine are now no longer confined to the specifically medical arena – they are taking on a wider ownership. This, in turn, is likely to have an influence upon how we approach those problems and, as a result, is likely to elicit new insights into them.

As a biologist, I am called upon to teach students studying on health-related courses. The teaching of subjects such as anatomy, physiology and pathology, which are my areas of specific biological interest, do not on the surface pose any significant problems. There are plenty of facts that can be handed on and plenty of books that can be recommended. But to do that is not to educate in the true sense. Teaching should not be merely a matter of transferring information from memory or written sources to receptive students – even if that is what students prefer. Ideally, one wants to make sense of one's subject and help others make sense of it too – always in the hope that they will make better sense of it and help you to a better understanding in return.

By 'making sense', I mean deriving some meaning from or insight into one's object of interest, not simply acquiring mere details. In other words, having a perception of the object of study in its own right rather than in how we are willing to perceive it. Making 'sense' in this way is not something that scientists do very often – certainly not at undergraduate level. We are too often concerned with just the details. It is noticeable that there is little 'sense' being made, that is 'meaning being derived', from our study of the human organism. It is true that we know a great deal about how our bodies work but the question of 'What does it all mean?' - that quintessentially philosophical question which nevertheless finds its way into physics – does not find its way into biology as often as one might expect. Yet our bodies are the material basis of our very existence. Without them we would not have being. Whether we continue in some form without bodies after death we must wait and see but I have no knowledge of myself before this body existed.

It has been said of the French philosopher Georges Canguilhem (1904-1995) that his work sought to uncover a philosophy of life rather than a philosophy of biology, that is, he sought a philosophy of the object of biological study rather than a philosophy of the human enterprise called 'biology'.

My object of study is the human organism and what the concepts of disease and health mean for it. Disease and health are such commonly used words that, when speaking about them, I have come to reverse their order. Normally, an English speaker refers to 'health and disease' but I have reversed their order so that, being used differently, these words might provoke a little more thought. At least, the question "Have they printed those words in the wrong order in the programme?" might get asked.

'Disease' and 'health' are ordinary, non-technical words used in everyday language; they are not the preserve of the medical profession. The roots of these words date from long before the establishment of modern scientific medicine. They are words born of common experience. But, at the same time, it is often said that a technical definition of disease and health is important and that these words are central to modern healthcare and have a bearing upon individuals and society. Indeed, whether a person is deemed healthy or otherwise affects a variety of social and economic rights, entitlements, exemptions and accountabilities. The concepts of 'disease' and 'health' are also held to be important in the identification and treatment or non-treatment of certain physical and mental states and help clarify the goals and limits of individual therapies and medicine as a whole.

Similarly, if one is teaching Health Science, or Health Studies, one might assume that some definition of what 'health' is ought to be evident within the programme. Likewise, 'disease', since, perhaps ironically, a lot of health-related teaching revolves around the study of disease.

Disease and health are words that are applied to our mental as well as our physical states. There is debate about whether this is entirely appropriate but that is a separate argument. I should point out that it is with reference to the latter, to physical states, that I am chiefly concerned. Just as we have no existence, so far as we can be sure, without a body neither can there be disease or health without a body. Disease and health should not be seen in isolation from the object to which, as concepts, they are applied.

Given our association with our own bodies, it is not surprising that we all, it seems, have a notion of what health is. But when we come to be more precise, we have difficulties. Many adopt uncritically the WHO definition that 'Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity'.

That they do this is probably not because it is a definition that informs but because it is a definition that is agreeable, reflecting something of that inexpressible notion of health we all seem to have. There are those, however, who do not find this definition adequate.

Some, having tried to define 'health' and being unsuccessful, have turned their attention to disease, arguing that if health could, indeed, be defined as the absence of disease then defining disease allows an alternative way of getting to a definition of health. But defining 'disease', they have found, is equally problematic.

In trying to define the concepts of disease and health, one of my favourite quotations from the literature is:

'In the last quarter of the 20th Century we have been witnessing an intense discussion on the nature of health ... and disease and on the meaning of these ... basic notions of medicine. The discussion seems to have ended up a blind alley, however.' (Sadegh-Zadeh, 2000)

I would suggest that the "discussion" referred to here has, in fact, become an extensive and complex debate and although, perhaps, two main schools of thought are usually identified, many different nuances of opinion have been expressed.

The two schools, or approaches, to which I refer are usually described as that of 'naturalism' (or sometimes 'descriptivism') and 'normativism'.

The naturalists argue that health is the absence of disease and that the term 'disease' can be understood objectively as biological functioning that is statistically below normal for the species concerned. Accordingly, they believe, this definition is uninfluenced by external human values. Naturalism tends to attract those of a more scientific way of thinking.

Normativists give emphasis to the subjective nature of disease experience which differs between cultures and through history. The classification of certain biological phenomena as diseases, it is argued, is based upon value judgements. The concept of disease is normative – where what counts as the 'norm' is prescribed rather than statistically derived. In effect, we decide what constitutes a disease. Normativism tends to be associated with those that I will describe as being of a more 'humanist' tendency.

I referred earlier to courses in 'Health Science' and 'Health Studies'. To some extent, the division into two separate programmes of study reflects the division into naturalism and normativism.

As noted, disease and health are everyday words; they are terms that belong to everyone. Importantly, it should be remembered how they evoke different perceptions in different people. Famously, Lynn Payer's book 'Medicine and Culture' (first published in 1988) gives a vivid account of how medical practice and explanation in four countries – France, pre-unification West Germany, the United States and Britain - differ. French doctors tended to focus on the liver as the primary site for concern while the German doctors tended to focus on the heart. In the US, the focus was on the effects of viruses and allergies whereas the Brits, although forever concerned with our bowels, characteristically kept a stiff upper lip. We were prescribed fewer drugs per capita than our French or German counterparts and, when visiting our doctors, were less likely to be diagnosed as 'sick' at all. If such differences exist between modern western nations in their use of scientific medicine, were Payer's study to be fully internationalised, the differences in practice and explanation would be even starker. One need only look at so-called alternative or traditional therapies – drawn from other cultures but now practised in our own – to see what a variety of interpretations exists.

More recently, in 2002, the 'British Medical Journal' carried out a survey on the Web asking readers to suggest what might constitute a non-disease. This term appears to have originated with Clifton Meador, writing in the 'New England Journal of Medicine' in 1965. It was used in the BMJ to mean "a human process or problem that some have defined as a medical condition but where people may have better outcomes if the problem or process was not defined in that way". As a largely invented term, one could be more prescriptive about its meaning – not that that simplified matters very much.

The exercise provoked a considerable correspondence demonstrating a variety of different perceptions about disease and health expressed by the medical profession and the general public alike.

In the words of the editor, "Some critics thought it was an absurd exercise, but our primary aim was to illustrate the slipperiness of the notion of disease. We wanted to prompt a debate on what is and what is not a disease and draw attention to the increasing tendency to classify people's problems as diseases." (BMJ 13^th April 2002)

Interestingly, some correspondents seemed quite irate at the suggestion that conditions that they had might not qualify for the label of a disease. Trying to read between the lines, one gets the impression that some were bemused that they might not qualify for the label 'disease' when they were clearly not 'healthy'. The issue of 'disease and health', we tend to assume, is something of an either/or situation.

Commonly, one finds disease and health being viewed as part of a continuum with healthy states at one end of a line and disease states at the other. Furthermore, if depicted graphically, it is not uncommon for a Gaussian, or normal distribution curve, to be introduced.

Disease and Health as a Continuum

The normal distribution that discrete physiological parameters often display and the state of the whole organism seem to merge. Adopting Cartesian conventions, pathological states are put on the left of the curve, to the lower or lesser end of the scale, and those in the peak of health to the right, at the distinctly positive end. The majority are situated in the middle and, being average, typify the normal or healthy state.

This is similar to the position generally adopted by the naturalist school of thought. But it also fits with another outlook, one that has been suggested as being common in most schools of medicine, nursing and the like - that of 'naïve normalism' which holds that to be healthy is to be 'normal'. Or should that be 'to be 'normal' is to be healthy'? The naivety comes from the ambiguity.

There are, in this perspective, a number of assumptions or attitudes that make the situation quite complex. Firstly, that disease and health are parts of a continuum. As far as I am aware, no case has ever been made that genuinely establishes this. This notion relies instead on our experience that sometimes one feels good and at other times one feels bad and that it is the same person that experiences all shades in between. It is the individual having these experiences that provides the continuity rather than disease and health that are continuous.

Furthermore, it is assumed that disease and health are both measurable using the same units, in the same way and on the same axis. I have not labelled the vertical axis because I do not know how to in this context. In biology, a normal distribution such as this usually refers to the numerical spread of cases within a given population. Are we dealing with populations or are we dealing with individuals? Any sense of a 'disease-health' continuity is only possible in terms of the individual. There can be no such continuity between individuals – across discrete organisms. However, the suggestion here is that to be healthy is to be like, or better than, the 'average' for one's species.

Then there is the assumption, which may seem odd even to question, that health is a more valuable state than disease. There are, in fact, biological interpretations that can be seen as challenging this point of view.

There may be further assumptions that could be addressed. This list is not meant to be exhaustive. But, given the problems we already see, it might be thought that the continuum idea is fatally flawed and that steps should be taken to avoid it. However, instead of trying to portray a disease-health continuum, it may be possible to describe something of the object – the individual – that experiences the continuity. That 'something' we might call the 'biological state' of the individual concerned.

The term 'biological state' – which I am coining - may appear a little vague. As I currently understand my own term, it is primarily a 'thinking tool'. Graphically, it may be represented thus:

'The Curve of Biological State'

Here the curve has been chosen for convenience rather than its precise representational qualities.

If the term 'biological state' is indeed vague, I believe that it is not inappropriate to be so, if done knowingly. In relation to disease and health, reference to biological 'function' is sometimes made but this term is only deceptively more precise; it is not without its own problems. Although there are philosophical problems concerning what we mean by the word 'function', irrespective of this, from a biological standpoint, disease and health cannot be related to function alone. Biologically, function cannot be divorced from structure or structures, be it at molecular or gross anatomical levels. There can be no function without an object to perform it. In turn, the structure of that object influences the performance of the function. To relate disease and health to function alone is to give an incomplete and, therefore, imprecise, explanation.

By adopting the term 'biological state', I am able to include an organism's structure and function simultaneously as well as other aspects of its constitution. This includes the genetic constitution of the individual - what instructions are (and are not) available to perform certain biochemical actions. Also, nutritional status, in the sense that diet influences the internal chemical environment and composition of the organism – it influences whether the necessary components are in place and how well a function or action can be performed. 'Biological state' relates to that which influences the make-up of the whole organism and its manifestations.

Some see biology as reducible to numerous, usually elaborate, chemical processes. These, in turn, may be reduced to physical forces. Indeed, much of biological research is reduced to the study of such phenomena. A bigger picture of the biological meaning of our object of study is somewhat lacking. In this, I include any notion of the 'biological meaning of disease and health'.

It is noticeable that all three of the main branches of science – physics, chemistry and biology – are concerned with behaviour; although that word is infrequently used in the way I mean. The behaviour to which I refer is the behaviour or interactions of matter. But whereas physics and chemistry consider matter in its rawest states, biology is about the behaviour of matter that is organized in ways quite unlike those encountered in either of the other two sciences. That, in terms of the history of the universe, physical factors preceded (and continue to underpin) chemistry and that chemistry preceded (and continues to underpin) biological organisms is not disputed. But these underpinning sciences are insufficient, in and of themselves, to completely explain biological material as organized matter and its interactive behaviour.

Perhaps, the following helps to demonstrate this:

Organisational Levels of the Organism

(From: McMurtrie & Rikel, 1991)

This is my favourite visual aid - I use it every year with as many groups of students as I can. There are various conceptual points that I try to bring out in using it.

Firstly, consider the arrows. They run from left to right - from the chemical and molecular level to that of the organism as a whole. This represents the way in which most textbooks of anatomy and physiology – certainly those directed at students of 'health' – are now constructed. After a few general comments, they tend to consider first basic chemistry. Then they move on to cells, then tissues, then physiological systems which are described and built up organ by organ. But they never, in fact, get to the level of the whole organism. There is never a final chapter that ties everything together. That seems to be left to common knowledge or subjective experience. Since we are all organisms, it is assumed that we know what organisms are. In this there is perhaps more than a hint of the 'we all know what health is' type of thinking.

This division into levels looks perfectly reasonable but this picture gives, in fact, a mixed message. All the divisions appear to be anatomical or structural in some way. However, 'systems' are, in fact, physiological notions. That certain organs belong together reflects physiological interpretation. Indeed, the idea of systems may even be misleading, if held too rigidly, since often organs assigned to one system can have vital roles in another. For example, the kidneys are part of the urinary system and have an excretory role but at the same time they have a vital influence on the cardio-vascular system. That influence is such that a case for the inclusion of the kidneys as regulatory organs belonging to the cardio-vascular system could be argued. As we find out more and as we think more critically, a once neat separation becomes less so. This is no surprise and perhaps ought to be expected of an organism but it is not our prevailing way of thinking.

Also, there may be something missing, perhaps a whole level or two. Wherever we look in the body, we notice a certain structural principle. Organs, for example, the lungs and kidneys, are not merely made of lung or kidney 'tissue', as this division may imply. They are made of certain basic types of tissues, not necessarily tissue that is organ-specific. These tissues are, however, organised in specific ways into, what I refer to in my teaching as, 'functional units'. It is here that the organ's key activities are performed. The lungs are composed of 'functional units' called alveoli; the kidneys of 'functional units' called nephrons. To form an organ, these 'functional units' are duplicated, sometimes many thousands of times, and held together with connective tissue. The principle appears to be applicable to all organs.

I do not know where the notion of dividing the organism into levels like this comes from. Certainly it can be found, for example, in writings associated with Arthur Koestler who used a similar division thus:

• Organism

• Organ systems

• Organs

• Tissues

• Cells

• Organelles

• Molecules

• Atoms

• Sub-atomic particles

• ???

Noticeably, he also omits the 'functional unit' level but adds those of the organelles and sub-atomic particles and beyond. Indirectly, he raises the question of where does reductionism end? In addition, I know of one other author who goes above organism level to include groups.

That said, we can use this idea of hierarchy to ask some fundamental questions – hence my liking for the previous diagram.

One question I like to ask my students is about what is alive in the body. If we move down the levels, we can agree that organisms are 'alive' – at least, that is how they present themselves to us. If one looks inside a living organism, we are happy to say that the organs are alive – at least, when they are transplanted we say that they need to be kept alive en route between donor and recipient. But can we say that systems are 'alive' in the same way? If a system is a physiological notion, can a physiological notion be 'alive'? Or should we think of a system as 'functional' so long as its component organs are 'alive'?

Cells can be observed alive under the microscope. Indeed, it is biological dogma that cells are the lowest unit of life. But can we say that tissues are 'alive' in the same way? Tissues are made of more than just cells – a lot of extra-cellular, non-living connective tissue, extruded from the cells, is involved. If we say that cells are 'alive' but connective tissue is not, what does that do to our notion that organs are 'alive' since they are made of both?

Going below cell level, we cannot say that the chemical or molecular components here are 'alive'. It is at this point that a jump between the 'living' and the 'non-living' is usually recognised. But the question of what we are to make of the mitochondrion, with its own DNA, living apparently symbiotically within our cells arises.

An organism is composed of more than living and non-living material; it also contains an amount of defunct, dead material that is being broken down, recycled or excreted. Even the developing embryo adopts precursory forms that are built up only to be broken down again on the way to becoming recognizably human.

Although this way of looking at organisms is quite common, questions such as these are rarely asked. In particular, two questions pertinent to us here are 'Where do disease and health reside in this hierarchy?' and 'Are they localized or generalized?'

Furthermore, how do we understand disease and health in relation to the 'living' material within an organism and in relation to its 'non-living' material? Alternatively, are disease and health aspects of the organisation of, rather than the type of, material involved? If that is indeed the case, disease and health become concepts that are not confined to biology. They become applicable to anything and everything that is organized.

These are not simple questions to answer and there are sure to be many more. I do not have any answers that I would like to offer at this stage. That is not really my point in asking such questions in the first place. Instead, the very act of asking such questions is meant to bring about an alteration in our preconceptions concerning the terms 'disease' and 'health' and of the object or objects to which these words are applied.

A serious error by my part of the academic community, I believe, is the way in which we, as biological scientists, accept attitudes and concepts about disease and health uncritically. Often we adopt ideas directly from medicine but we also adopt the more common uses of these words. As a result, humanitarian and anthropocentric attitudes are being imported into a science which should ideally be value-free. It is, of course, questionable whether any science is ever completely value-free (indeed, the goal of value-freedom, it can be argued, is a value in itself!). But even if complete value-freedom is impossible, we ought still to aspire to excluding confounding attitudes where they can be identified. Failure to do this has resulted in there currently being no singularly biological critique of the terms 'disease' and 'health'. Instead, there is the mere acceptance of prevailing attitudes, not least that of naïve normalism, noted earlier. Indeed, the question of whether the terms 'disease' and 'health' even have any independent biological meaning has yet to be fully explored.

Biology is usually understood to be the science or study of 'life' and, as such, it was the hope of the earliest modern biologists to be able to define what life was. But they were unable to do so. Now any desire within the biological community to define life has largely evaporated.

Claude Bernard in his 'Introduction to the Study of Experimental Medicine' (Introduction à l'étude de la médicine expérimentale, 1865) stated that, "the words, life, death, health, disease have no objective reality."

Irrespective of whether one agrees with this, Bernard does draw our attention to a concept that gets little biological interpretation – death. In English, the word can mean both the process of dying and the state of being dead. Both interpretations deserve attention in relation to trying to understand life.

In order for something to be able to be dead, it is necessary for it first to have been alive. One must also go through some process of attaining the state of being dead, whether that process is protracted or near instantaneous. Barring the 'near instantaneous', can the transition from 'alive' to 'dead' ever be disease-free or is there a completely healthy dying? Then again, we might ask, what distinguishes a disease that leads to death from one from which one can recover or with which one can learn to live?

Importantly, where on the previous disease-health continuum, do 'dying' and 'dead' fit? Certainly, both need to be accommodated somewhere. Does 'dead' perhaps belong even further left than disease – to the left of the vertical axis even? If so, on this type of graph, death would be infinite – in which case it would tend to take on somewhat poetic overtones.

Being dead might not, at first sight, appear to be a biological state at all. Life, disease and health all denote something to do with a state of animated matter whereas being dead denotes the same matter that has been de-animated. Something that is dead is something that no longer has its former animation. However, the once animate body may still exist. Therefore, we could describe someone or something that is dead as having a biological state below a critical level. They are not dead upon reaching a 'zero' biological state. That state occurs only when the organism's material is totally dissipated – as occurs, for example, following cremation.

The Curve of Biological State

Since biological state relates to all aspects of an organism's constitution – its structure, function etc. – bodily remains, exhumed after even considerable periods of time, can be said to have a certain biological state albeit one that is primarily structural and fragmented. On the other hand, a fossil, many millions of years old, in which the original material has been entirely replaced by other minerals, is a replica of a former biological state since the original material laid down during life is now lost. One may even go so far as to say that for a biological object to be dead, there has to be some persisting material that can be described as 'dead'. Otherwise the object simply no longer exists.

Objects that demonstrate what we call 'life' are the result of the process of evolution. Our understanding of evolution is central to our understanding of biological objects. It is quite simply biology's greatest contribution to human understanding - and not merely to the understanding of biological objects. Evolutionary theory is biology's greatest contribution to understanding ourselves. It casts us in a less anthropocentric context. We are fellow players in a much larger biological drama that began many millions of years before we entered the scene and which is capable of going on long after we have left. It, therefore, allows us to see ourselves in a more material and less self-aggrandized way. But although evolutionary theory allows this, such an understanding of ourselves is not yet fully explored. Modern evolutionary theory is still relatively new, continues to be developed and its application to humans has sometimes proven to be controversial, as the example of socio-biology – now called evolutionary psychology - testifies.

René Dubos noted in 1968 that:

'Physiological tests reveal that modern man has retained many … physiological and mental attributes ill suited to civilized life, just as he has retained useless anatomical vestiges from his evolutionary past. As a result, he must meet the challenges of today with biological equipment largely anachronistic. Many forms of organic and mental disease originate from the responses that man's Paleolithic (sic) nature makes to the conditions of modern life.'

But it is only in the last decade or so that the field of Darwinian (or probably better, evolutionary) medicine has been pioneered, championed primarily by Randolf Nesse of the University of Michigan. This began in earnest in 1991 with the publication in 'The Quarterly Review of Biology' of an article entitled 'The Dawn of Darwinian Medicine' and reached popular attention in the mid-1990s with the book published in the US as 'Why we get Sick' and in the UK as 'Evolution and Healing'. (Nesse, a physician specialising in psychiatry, co-wrote both of these books with the evolutionary biologist, George Williams.)

Darwinian medicine is the enterprise of trying to find evolutionary explanations for vulnerabilities to disease (Nesse).

It is Nesse's contention that all medical students should be taught evolutionary theory or at least evolutionary theory as it can be related to medicine. As a result, it is envisaged that this will influence how medical practice is best used to treat patients.

Hence Fabrega (1997) has suggested that evolutionary medicine is '[the pursuit of] how evolutionary theory can sharpen the efficacy of medical practice'.

Although within this field, some focus on the maintenance of health has been given by Boyd Eaton of Emory University, Atlanta and his co-workers, the main emphasis in Darwinian medicine is on the understanding of disease from an evolutionary perspective - to understand, for example, why we are not 'designed' better and why we have not evolved ways to avoid succumbing to certain conditions, infectious and non-infectious. This emphasis on disease reflects a medical, rather than a biological, impetus.

Because Darwin belongs to biology, it is easy for biologists and others to assume that Darwinian medicine is about a reappraisal of the biological objects of medicine: a biological reappraisal of physical processes associated with what we call disease and health. Although this does occur, Darwinian medicine is more accurately viewed as being a reappraisal of medical practice in the light of evolutionary biology. For a long time, biology has serviced medicine in largely technical ways. Now the conceptual aspects of biology's evolutionary theory are also being transferred. These concepts are, however, only likely to gain medical attention and acceptance where they can be seen to be of practical benefit. That being the case, there is a danger that evolutionary theory could be used in an incomplete or even distorted way.

As I suggested earlier, as biologists, we have been too ready to accept attitudes and concepts about disease and health from medicine and elsewhere without due criticism. Applying evolutionary theory to the question of disease and health via Darwinian medicine, while keeping to standard medical attitudes, certainly does not overcome that problem. Biologists need instead to apply evolutionary theory to the question of disease and health without any preconceived attitudes – that is, from a purely biological perspective – and not admit even humane or humanitarian attitudes.

Medicine's concerns are 'proximate'. It is concerned with the patient's condition as it presents. It is concerned with that condition's containment, treatment and, where possible, its cure. Within an evolutionary context, biologists, including those active in Darwinian medicine, are interested in 'ultimate' explanations to questions of how the current biological situation came about. Some of the answers to these questions involve events that occurred millions of years ago when what gave rise to our current 'biological state' began to evolve.

A frustration for a biologist interested in the concepts of disease and health comes from the way in which most of the current literature on the subject takes a somewhat proximate, humanist and anthropocentric stance. Darwinian medicine introduces a potential break with this approach and allows disease and health to be seen in a more objective manner. Darwinian medicine holds distinct possibilities for a non-medical, biological interpretation of disease and health. For courses in 'Health Science', the approach thus offered may prove to be paradigmatic. As I mentioned earlier, such courses tend to be associated with departments of biological science. It is here that we are more likely to be able to exclude the attitudes and influences that govern the clinic. But, as I have said, so far we have not been alert enough to do this.

Biologically, it is evident that what we call 'disease' can actually shape a species and even assist in its survival. The famous example of sickle cell anaemia demonstrates this. In the malarial areas of central Africa, to have sickle cell trait – as conferred by a specific genotype – is reproductively advantageous by comparison with those with the 'standard' and the sickle cell genotypes. Those with sickle cell trait are better able to survive and have relatively more offspring, or offspring surviving to adulthood, than do the others. But at the same time, those with sickle cell trait experience bouts of illness. That they are, on average, reproductively more successful is usually unknown to them and is of questionable comfort. This example suggests that individual suffering is beneficial to species survival and that disease can, in a real sense, be a 'good' thing – if 'good' is the appropriate word. It is not a good thing for the individuals affected but it is in species terms – the species avoids extinction.

There is a tendency among some biologists to see almost everything in terms of how it relates to relative reproductive success. Indeed, of the factors necessary for natural selection to operate, reproduction is the first and foremost.

There can be no natural selection unless entities have a means of reproducing to form a new generation. There must also be a mechanism of heredity. Offspring must be like their parents but there must also be variation. Offspring must be able to differ from their parents in specific characteristics.

As part of this, there will also be differential 'fitness', that is, the products of the above will differ in their ability to reproduce. In different environments, some forms will be better able to reproduce than others.

Having mentioned earlier that if we were to consider disease and health as aspects of organisation rather than of the type of material involved then as concepts they become applicable to anything that is organized, I should also note here, in passing, that none of the conditions necessary for the operation of natural selection require that the evolving object be a biological entity. These conditions apply equally to, for example, a computer virus.

Although normally interpreted in population terms, all of these features are expressed via the individual. Consequently, there is a sense in which, conceptually, Darwinian medicine does not go as far as it might because the biology from which it springs is restricted. There is something that medicine has that biology lacks and, I believe, needs to acquire, namely, a fully developed biological appreciation of the individual – what might even be called a 'biology of the individual'. It is only via the individual that natural selection works and only via the individual that species are ultimately affected. It is only via the individual that disease and health are expressed – not to mention 'life' and 'death'. The sickle cell anaemia example demonstrates this. But as biologists, we tend to overlook this because we are used to population thinking.

Organism level biology usually explains what it observes in terms of populations, or groups within populations, or even in terms of gene frequencies. It adopts the standard statistical approach of finding the mean and equating that with the norm. It never thinks in terms of specific individuals in the way that medicine must. No two medical cases are ever exactly identical because the 'biological state' of each individual is unique. However, in biology, any notion of individual 'biological state' is currently missing, lost, subsumed into the means and standard deviations of the crowd.

A biology of everyman is a biology of no man.

Instead of reproductive success – which can only really be assessed in group terms - we might consider casting our attention on the survival of the individual. There seems to be an innate, evolved desire in human beings to live for as long as possible and also, perhaps, as comfortably as possible. Interestingly, this strategy, although fundamentally self-seeking, does in fact, have reproductive consequences. The longer one is able to survive, the more likely it is that reproductive opportunities will arise. The better one lives, by having sufficient food, shelter etc., the better one's 'biological state' is likely to be and the more likely one is to produce viable offspring, able to live potentially long reproductive lives of their own.

Certainly, there are examples of organisms that are genetically programmed to mate or spawn only once and die in the process. But these are organisms that are able, on those occasions, to produce numerous offspring that need no parental investment for survival. It is different for those, such as ourselves, that produce relatively few helpless offspring per pregnancy and which need to exercise considerable parental investment in getting those offspring successfully to maturity. For such organisms, individual survival has a direct effect on species survival.

Importantly, this 'survival instinct' is expressed individually and, whereas reproductive rates can be quantified and averaged out, the urge to survive – the urge to live – cannot. Perhaps an indirect measure is length of life, although this is a rather poor parameter since it is influenced by numerous extraneous factors. But such is the urge to live that, in the West, many are happy to go on long after the culmination of their biological contribution to their species. Modern medical technology also allows otherwise helpless individuals to be kept from dying under somewhat artificial circumstances. That we have allowed this suggests something about our innate attitude to life. It is different for other members of the animal kingdom. For them, survival entails not merely staying alive but also remaining able to perform the very tasks that keep them alive.

Our existence is dependent on our physical bodies. To consciously hang on to our bodies is to hang on to our conscious existence, so far as we can tell. These bodies, our attitudes to them and to the animation we call life - even our desire to live - have each been shaped by a process of evolution that does not work according to human ethical standards. Accordingly, the place of disease and health in the biological world is not the same as that in medicine. In our current biology, processes that have been medically labelled as 'disease' can be seen as having effects that shape a species for survival. A 'disease' does not automatically have an entirely deleterious effect - that is so far as groups are concerned. In the earlier example, those with sickle cell trait may be found to be reproductively more successful as a group but their individual 'biological states' are not necessarily superior to those of individuals with the 'standard' genotype. It is only when the latter become infected with the malaria parasite that the situation changes – only at that point is the latter's biological state altered for the worse. Thus, using the same data, a biology of the individual may give a different interpretation to that provided by our present biology.

To get out of the blind alley that the discussion about disease and health seems to have ended up in, may require an altered view of medicine and an altered view of biology. It should not be assumed that our current perspectives are complete and entirely accurate. That said, I am of the mind that, irrespective of the needs of the medical profession for ethical insights on the matter of what disease and health entail, not being able to define these concepts is a potentially more productive situation for the biologist. Without the problems that these words generate, certain questions about how we understand the human organism may otherwise go unasked – let alone unanswered.

I no longer look at the problem of the concepts of disease and health in terms of how we might get a definition of what these words mean. Instead, these words raise important questions, not only about what it is that elicits the need for and use of those words but also about how we understand ourselves as biological objects. The words 'disease' and 'health' are useful tools for describing some quality or qualities of the organism which can then be investigated. Importantly, these concepts raise questions about the need for a biology of the individual. This in turn suggests a place for an emphasis on individual survival, as opposed to group reproductive success, as a way of understanding organisms, in particular, ourselves.

In addition to the usual medical place that the concepts of disease and health occupy, there is a perhaps more fundamental distinctly biological place that they occupy in human existence. It is a place that still remains to be explored and explained in the appropriate biological terms. I hope that this has given an indication of the some of what this may entail.

References:

Dubos, R. (1970). Man, Medicine, and Environment. Harmondsworth, Pelican.

Fabrega, H. (1997). Evolution of Sickness and Healing. Berkeley, University of California Press.

Koestler, A. (1978). Janus: A summing up. London, Picador.

McMurtrie, H. and Rikel, J.K. (1991) The Coloring Review Guide to Human Anatomy. Wm C Brown Publishers. Dubuque.

Meador, C. (1965). The Art and Science of Nondisease. New England Journal of Medicine 272(2): 92-95.

Nesse, R. and Williams, G. (1995). Evolution and Healing. London, Weidenfeld and Nicolson.

Payer, L. (1988). Medicine and Culture - Varieties of treatment in the United States, England, West Germany, and France. Harmondsworth, Penguin.

Sadegh-Zadeh, K. (2000). Fuzzy health, illness, and disease. Journal of Medicine and Philosophy 25: 605-638.

Williams, G. and Nesse, R. (1991). "The dawn of Darwinian medicine." The Quarterly Review of Biology 66: 1-22.

A transcript of the lecture given at the International School of Philosophy and History of Biology and Medicine summer course on Epistemologies of Medical Knowledge and Practice, in Nettuno, Italy, 29th September - 2nd October 2003.