The Role of Medicine: Dream, Mirage, or Nemesis?

by Thomas McKeown

Overview

In analyzing the factors that have improved health and enhanced longevity during the last three centuries, Thomas McKeown contends that nutritional, environmental, and behavioral changes have been and will be more important than specific medical measures, especially clinical or curative" measures.

Originally published in 1980.

The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.

Product Details

ISBN-13:	9780691616360
Publisher:	Princeton University Press
Publication date:	07/14/2014
Series:	Princeton Legacy Library , #56
Pages:	226
Product dimensions:	9.90(w) x 6.90(h) x 0.50(d)

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The Role of Medicine

Dream, Mirage, or Nemesis?

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By Thomas McKeown

PRINCETON UNIVERSITY PRESS

Copyright © 1979 Thomas McKeown
All rights reserved.
ISBN: 978-0-691-08235-6

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CHAPTER 1

Evolution of Health Concepts

The aims of this book are: (a) to examine the validity of a concept which is rarely stated explicitly but on which medical activities largely rest, namely that human health depends essentially on a mechanistic approach based on understanding of the structure and function of the body and of the disease processes that affect it; and (b) to consider the significance of the conclusions for medicine, particularly in relation to health services, medical education, and medical research. These themes are discussed in the three sections into which the book is divided, the first two concerned with concepts and determinants of health and the third with the role of medicine.

Although the mechanistic approach is predominant it is not the only one which has been taken to improve man's health. In his splendid account of the evolution of health concepts Dubos referred to the dual nature of medicine which resulted from ideas which have been promoted with varying emphasis in all periods down to the present day: health preserved by way of life and health restored by treatment of disease. Both are to be found in the classical tradition:

The myths of Hygieia and Asclepius symbolise the never-ending oscillation between two different points of view in medicine. For the worshippers of Hygieia, health is the natural order of things, a positive attribute to which men are entitled if they govern their lives wisely. According to them, the most important function of medicine is to discover and teach the natural laws which will ensure a man a healthy mind in a healthy body. More sceptical, or wiser in the ways of the world, the followers of Asclepius believe that the chief role of the physician is to treat disease, to restore health by correcting any imperfections caused by the accidents of birth or life.

The preservative approach was certainly in the minds of the social and medical reformers of the eighteenth and nineteenth centuries, and it is to be found in the public health activities which resulted from their efforts and have continued and developed to the present day.

Philosophically the seventeenth century was a turning point in the balance between the two concepts. Galileo had shown that scientific methods were capable of providing a mechanical interpretation of the physical world, and Descartes saw no reason why the same principles should not be extended to living things. He conceived of the body as a machine, governed entirely by the laws of physics, which might be taken apart and reassembled if its structure and function were fully understood. His theories seemed to find confirmation in the first major development in modern physiology, Kepler's description of the dioptric mechanism by which the eye produces the retinal image. This advance resulted from the application of technical knowledge available in second-century Alexandria, but which no Greek would have thought of bringing to the study of the living body. A little later there was an even more dramatic demonstration of the validity of the mechanistic approach in Harvey's discovery of the circulation of the blood, which Descartes, needless to say, warmly welcomed.

In the present context there are three aspects of the hypothesis to be considered: the relation between mind and body; the body interpreted as a machine; and the body controlled as a machine.

The first subject need not detain us, although it has been the focus of endless controversy at the interface between science and theology. Briefly, while Descartes as a scientist could accept a physical explanation for the body, as a religious man he was unable to accept it for the mind; so he found it necessary to distinguish between mind and body, and he introduced what Ryle described as the Category-mistake, the notion of the mind as a ghost in the body as a machine. Temporarily at least, this explanation furnished a reconciliation of sorts between the results of the new science and the traditional doctrines of the soul. However, although this problem has engaged the attention of philosophers and theologians for centuries, for many scientists educated since the First World War I suspect it has scarcely existed. Unencumbered by preconceptions derived from religion or scholastic philosophy, they have never thought of the mind as something which exists apart from the physical structure of the body. Their problems arise mainly from the other implications of the Cartesian hypothesis: the body conceived as a machine and the body controlled as a machine.

There is no difficulty today in accepting that the body can be understood as a machine, of which knowledge has advanced continuously from the seventeenth century; slowly at first, but very rapidly at the cellular level since the nineteenth century and at the molecular level in the twentieth. In parallel with the understanding of structure and function there was an increase in knowledge of disease processes, including, in the case of infectious diseases, recognition of disease agents. It is hardly surprising that the transformation of human health which occurred in the same period was attributed to the new knowledge, and that the improvement in the performance of the body as a machine was assumed to be due to its control as a machine.

However, this is an assumption which must be examined carefully. In the first place it should be noted that in the past three centuries conditions of life have improved more than in any previous period in man's history. For large populations the chronic problem of malnutrition has been solved; some of the most serious threats, particularly those associated with water and food, have been removed from the environment; and for the first time on an extensive scale human populations have limited their reproduction to a level consistent with basic resources. In assessing the contribution of medical measures based on understanding of the structure and function of the body, it is clearly essential to consider the extent to which the advance in health was due, not to intervention in the working of the machine, but to improvement in the conditions under which it operates.

There is another reason for caution before endorsing the conventional explanation for the advance in man's health: the fact that quite a different interpretation must be accepted for the improvement in health of other living things. The brief discussion which follows will be concerned with animals, although many of the conclusions would be equally true for plants.

The key to the riddle presented by the health of living things is the relation of fertility to mortality. Both have evolved through natural selection; but they have not evolved in balance, in the sense that numbers born are restricted with regard for the resources of the environment and the numbers that can survive. A contrary view, that animals limit their reproduction by social and biological restraints was strongly challenged, and since it has no relevance to human experience in the past few centuries it will not be considered here.

The alternative, and I believe the more convincing interpretation, suggests that the size of natural populations is controlled by density-dependent mortality. In wild birds and some other animals (Lack mentioned carnivorous mammals, certain rodents, large fish where not fished, and a few insects) the level of mortality is determined mainly by the availability of food. However, there are other animals, possibly many more, in which, although numbers are limited ultimately by food supplies, these limits are not usually reached because population size is restricted by predators, including insect parasites, and disease. On this interpretation the essential requirements for reduction of mortality and improvement in health of animal populations are (a) equating of food supplies and population size, by increasing the amount of food and limiting numbers, and (b) removal of other causes of mortality, particularly predators, including in some cases human predators, and parasites.

This theoretically derived programme is in accord with what has actually happened in domestication of plants and animals. Their numbers and distribution are controlled; more and better food is provided: manure and fertilizers for plants, foodstuffs in a variety of forms for animals; and domesticated plants and animals are protected so far as possible from environmental hazards.

Another method of outstanding importance is selective breeding, which has been used with all domesticated animals except the elephant. (Elephants rarely breed in captivity.) This approach has been employed to accentuate characters desired by man, sometimes with side-effects on health from production of pure strains which are less resistant to microorganisms. But cross-breeding has been used to produce hardier stocks by heterosis.

The methods which have been exploited in plant and animal husbandry are essentially population methods which owe little to understanding of structure and function. It is fairly obvious why this approach has been preferred to physical or chemical manipulation of individual plants or animals. In the first place, except in the case of pets and unique specimens such as racehorses and prize animals, man has little interest in individual examples of species other than his own. Secondly, it is more economical to deal with large numbers in preference to identifying and controlling single specimens. And finally, a conclusion which is particularly important for human health, population methods are far more effective than individual methods. Indeed, when they are fully applied there is little need for direct intervention, for under favourable conditions the large majority of those born alive remain healthy.

To what extent is it possible to extrapolate from other animals to man? Until the eighteenth century the human situation was analogous to that of animals in their natural habitats; numbers born were greatly in excess of numbers that could survive, and population size was limited by density-dependent mortality. There is no evidence of effective restriction of population growth, either by deliberate control of reproduction or by instinctive restraints of the kind suggested by Wynne-Edwards in other animals. The high level of mortality was due to starvation, disease, and homicide in its multiple forms.

In these circumstances human health provided scope for the methods which led to improvement in the health of domesticated animals. Like other living things, man has been exposed to rigorous natural selection, and the large majority of those born alive are healthy in the sense that they are adapted to the environment in which they live. The primary need is for sufficient food, which requires both an increase in food supplies and limitation of numbers. Man also needs protection from certain hazards in the physical environment, particularly those which lead to exposure to infective organisms. The notable difference between human and other animal experience in relation to health results from ethical restraints which prohibit public control of reproduction. But man is uniquely educable, and can learn voluntarily to limit family size. In this way a self-imposed behavioural change may achieve the same result as the restrictions applied to other animals.

However, the approach to biology and medicine established in the seventeenth century was an engineering one based on a physical model; its consequences are even more conspicuous today, largely because the resources of the physical and chemical sciences are so much greater. Physics, chemistry, and biology are considered to be sciences basic to medicine; medical education begins with study of the structure and function of the body, continues with examination of disease processes and ends with clinical instruction on selected sick people. Medical service is dominated by the image of the acute hospital where the technological resources are concentrated, and much less attention is given to environmental and behavioural determinants of disease, or to the needs of sick people who are not thought to provide scope for investigation or treatment. Medical science also reflects the mechanistic concept, for example in the attention given to the chemical basis of inheritance and the immunological response to transplanted organs. These researches are strictly in accord with the physical model, the first being thought to lead to control of gene structure and the second to replacement of diseased organs by normal ones. The question therefore, is not whether the engineering approach is predominant in medicine, which would hardly be disputed, but whether it is seriously deficient as a conceptualization of the problems of human health.

The first two parts of this book are concerned with an examination of this issue. There are at least three approaches which might be taken to assessment of the determinants of human health. One possibility would be to examine, where possible by controlled trials, the effectiveness and efficiency of medical procedures and services, as well as other influences, such as food and hygiene, which contribute powerfully to health. This approach has been employed with great advantage in a limited number of cases; but it presents formidable technical, ethical and administrative difficulties and it is hardly conceivable that within the foreseeable future it could provide a comprehensive appraisal of all the major determinants of health. I have therefore restricted attention to the other possibilities.

Chapter 2 outlines a conceptual approach. It suggests that if we are thinking of disease origins rather than disease mechanisms, the most fundamental division is between abnormalities determined irreversibly at fertilization and those which are manifested only in an appropriate environment. Among the latter there is an important practical distinction between congenital conditions in which the environmental influences are pre-natal and those, including most common diseases in which they are probably post-natal. Although post-natal influences vary greatly in type, it is suggested that it is on their identification and control that hopes for the solution of the problems of the common diseases largely rest. This approach can often succeed in spite of deficient knowledge of disease mechanisms.

The next three chapters present the third approach, an examination of historical evidence; they are based on data for England and Wales which are perhaps the most satisfactory for this purpose. It is shown that the decline of mortality, the main evidence of improvement in health, was due essentially to a reduction of deaths from infectious diseases. (The only non-infective causes which appear to have decreased substantially before the twentieth century were infanticide and starvation.) Chapter [4 investigates the reasons for the decline of the infections, and Chapter 5 considers non-infective conditions which were associated with about a quarter of the reduction of mortality since 1900.

The conclusions concerning the determinants of man's health are brought together in Chapters 6 and 7, which examine man's health experience in four periods: nomadic, agricultural, transitional and industrial. The predominant influences which led to the improvement in health in the past three centuries were nutritional, environmental (particularly control of water and food), and behavioural; the last through the change in reproductive practices which limited population growth. The major influences are reconsidered in the light of the change in health problems which followed the decline of the infections, and it is concluded that in advanced countries health is still determined mainly by personal behaviour and the environment. However, there is this difference, that the influences which result from the individual's behaviour (smoking, diet, exercise, etc.) are now relatively more important than those which depend on action by society. The contribution of personal medical measures remains tertiary in relation to the predominant behavioural and environmental influences.

Chapter 8 assesses medical achievement in relation to prevention of death, postponement of death (from a specific cause) and treatment of non-fatal illnesses. The conclusions drawn in respect of non-fatal illnesses are not essentially different from those for fatal conditions: that while symptomatic relief can be provided for some, perhaps all patients, with some notable exceptions the underlying conditions cannot at present be cured.

Part Three discusses the implications of these conclusions for medicine. In relation to non-personal health services (Chapter 9) there are two important issues. One concerns public action required in the light of recognition of the significance of behavioural and environmental determinants of health; the other is related to the extent of medical involvement. Many people would say that such matters can safely be left in the hands of other health workers, a view that has attractions for some doctors who would be glad to be rid of responsibility, particularly for non-personal services. However, it is argued that a contribution is needed from medical specialists in environmental medicine and from all practising doctors in relation to patients' behaviour which prejudices their health.

(Continues...)

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Excerpted from The Role of Medicine by Thomas McKeown. Copyright © 1979 Thomas McKeown. Excerpted by permission of PRINCETON UNIVERSITY PRESS.
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Table of Contents

• FrontMatter, pg. i
• Contents, pg. v
• Preface to the Second Edition, pg. vii
• Introduction, pg. xi
• 1. Evolution of Health Concepts, pg. 3
• 2. Inheritance, Environment and Disease, pg. 12
• 3. Decline of Mortality, pg. 29
• 4. Infectious Diseases, pg. 45
• 5. Non-Infective Conditions, pg. 66
• 6. Health in the Past, pg. 71
• 7. Health in the Future, pg. 79
• 8. Medical Achievement, pg. 91
• 9. Non-Personal Health Services, pg. 117
• 10. Clinical Services, pg. 131
• 11. Medical Education, pg. 143
• 12. Medical Research, pg. 156
• 13. Dream, Mirage or Nemesis?, pg. 176
• 14. Medicine as an Institution, pg. 190
• Index, pg. 199