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Evolution and Health

by Stephen Boyden ©

(Boyden, S.V. (1973), "Evolution and Health". The Ecologist, Vol. 3, No. 8 (Aug. 1973), pp. 304-309.)

In our attempts to view the human situation in meaningful perspective, it is essential that we take account not only of our cultural background, but also of our biological history. For the human species evolved in an environment very different from that to which most of us are exposed today, and it was this evolutionary environment which determined, through natural selection, the innate characteristics of the species. While this fact has important implications for many of the major problems facing human societies today, this paper concentrates for the most part on a single aspect, namely, the biological history of Homo sapiens as it relates to problems of human health and well-being in the modern world. It concludes, however, by suggesting that this evolutionary approach to the health requirements of the human organism can lead to insights of relevance not only to public health, but also to the major social problems of our times, including the ecological predicament.

For the purposes of this article, I define "biological determinants of optimal health" as those various conditions which tend to promote or permit optimal physiological, mental, and social performance in an animal in its "natural" or evolutionary environment. They may also be defined as those various conditions which tend to promote the kind of functioning of mental and physiological processes most likely to ensure the survival and successful reproduction of the individual in the natural environment. Whereas, in the case of human beings, this degree of health is certainly not necessary for survival and reproduction under modern urban conditions, I contend that it is nevertheless a most desirable objective in terms of life enjoyment.

The Darwinian theory of evolution through natural selection assumes that populations of animals are heterogeneous, in the sense that there are inheritable differences between individuals, and that, because of these differences, in any given set of circumstances certain individuals are more likely than others to survive, reproduce, and successfully rear young. The individuals which are better suited to the prevailing conditions tend to contribute more to the genetic constitution of subsequent generations than do those which are less well suited, so that eventually the population as a whole tends to become better suited to these conditions. From time to time, changes spontaneously occur in the genetic material (due to recombination, mutation, etc.). If an individual carrying such new genetic characteristics is, as a result of the change, less well suited to the prevailing conditions and consequently less likely to survive and reproduce, then the new genetic material will, before long, be eliminated from the population. If, on the other hand, the individual with the new genetic characteristics turns out to be better suited than its fellow to prevailing conditions, it will tend to contribute more offspring to the next generation, so that eventually the new characteristics will spread in the population, ultimately replacing the less advantageous characteristics. Thus, over many generations, populations tend to become better and better suited to the environment in which they live.

Phylogenetic maladjustment

The important corollary to Darwinian theory that I wish to stress has not been given a name, but I shall refer to it here as the "principle of phylogenetic maladjustment". According to this principle, if the conditions of life of an animal deviate from those which prevailed in the environment in which the species evolved, the likelihood is that the animal will be less well suited to the new conditions than to those to which it has become genetically adapted through natural selection and consequently some signs of maladjustment may be anticipated. Obvious though this principle is, and obvious though it's importance, it is seldom referred to in the literature, and consequently its significance seems to have been largely overlooked. Although highly pertinent to the study of health and disease in mankind, I have not seen the principle mentioned in any of the standard textbooks of medicine. I have come across only two clear statements of the principle in the medical literature-one in the introduction to The Saccharine Disease by Cleave and Campbell (1966) and the other in Man's Presumptuous Brain by Simeons (1960).

The term "phylogenetic maladjustment",(note-The maladjustment is phylogenetic because it represents a characteristic response of the species to the changed environmental circumstances.) then, specifically refers to disorders which represent the reactions of organisms to conditions of life which differ from those to which the species has become genetically adapted in evolution through the processes of natural selection. This principle relates not only to environmental changes of a physiochemical or material nature, such as changes in the quality of food or air, but also to various non-material environmental influences, such as certain social pressures which may affect behaviour. Furthermore, signs of phylogenetic maladjustment may be physiological, behavioural, or both.

We can easily think of countless examples of the principles of phylogenetic maladjustment operating in Homo sapiens . The traditional "scourges" of mankind such as plague and typhus and the great deficiency diseases such as scurvy, beriberi, pellagra, and kwashiorkor are all straightforward examples of the principle. An examination of reports on the reasons why patients visit their physicians in the most developed countries in Western society today (e.g. Logan and Cushion, 1958) shows clearly that the majority of the disorders of which they complain fit into this category, and are "diseases of civilization", in the sense that they would have been rare or non-existent in primeval society (e.g. virus infections of the respiratory and alimentary tracts, peptic ulcer, cardiovascular diseases, obesity, diabetes, and probably much psycho-neurosis).

Removal of "optimum health"

It is worth emphasising that one of the most significant influences of civilisation on the biology of mankind has been the removal of "optimal health" as a prerequisite for individual survival and reproductive success. In the evolutionary environment, survival and reproductive success were dependent on superb physical fitness, acuity of vision and hearing, absence of debilitating or painful illness, mental alertness, a good memory, and a state of mind which permitted, when necessary, concentration, patience, and a willingness to co-operate with others. None of these attributes is necessary for the individual's survival and reproduction in the protective environment of modern society, although, clearly, many of them are important in relation to life enjoyment. This molly-coddling influence of civilisation has been referred to as "pseudoadaptation" (Boyden, 1970; 1972a. & b.) because, while it mimics true adaptation by allowing the survival and multiplication of human populations under changed environmental conditions, it differs from true adaptation in that it does not involve any active response on the part of the individual or of society, and consequently the forms of maladjustment are permitted to persist indefinitely.

Before proceeding further, it may be as well to refresh our memories on a few aspects of human evolution. It appears now that there were already beings on earth at least two million years ago conforming to Leakey's (1961) definition of "man" (i.e. an animal that makes tools to a set and regular pattern). These people were, of course, rather different from ourselves in that their cranial capacity was about half that of modern man and there were other morphological, and no doubt behavioural differences.

By 300,000 years ago, however, human culture was perpetuated by beings who differed only slightly from modern mankind in their physical characteristics, although the average size of their brains was still somewhat less than the modern average. But our ancestors of 60,000 years ago had a cranial capacity at least as big as ours, and they are classified as belonging not only to the same species as ourselves, but also to the same subspecies, namely Homo sapiens sapiens.

That was some 2,400 generations ago. It was not until about 400 generations ago that, in certain regions of the world some of our ancestors, for reasons unknown to us now, gave up the nomadic hunter-gatherer way of life for a new kind of economy based on the domestication of plants and animals for food production and on a lot of hard work. This domestic transition was thus a very recent even in the biological history of mankind. Accordingly, we can safely infer that the innate phylogenetic or species characteristics of mankind were determined by the selection pressures operating in the primeval environment and were already established by the time of the advent of civilisation. (note-"Primeval" in this paper refers to the long hunter-gatherer period of human existence before domestic transition.) In the context of the present paper, the important point is that the innate biological determinants of human health were established under primeval conditions, and any innate needs that mankind may have for survival or well-being could be satisfied under those considerations. It follows from these considerations, and from the fact that Homo sapiens is no exception to the principle of phylogenetic maladjustment, that any deviation that can be recognised from the primeval conditions of life must be suspect as a possible cause of physiological or behavioural disorder. For this reason, knowledge of the biological conditions of life of primeval mankind is distinctly relevant to our concern for the health and well-being of mankind now and in the future.

Let us attempt, therefore, a very brief description of the biology of human beings in typical primeval society in much the same way as we might describe the biology of the jack rabbit, the mountain gorilla, or any other animal species (except that, in the case of Homo sapiens, we do not have to make a special effort to resist the temptation to anthropomorphise).

The following description is written in the past tense, although many of the data on which it is based are derived from the work of anthropologists on existing (or until recently existing) hunter-gatherer societies. (note-The description is based partly on justifiable inferences derived from general biological principles and partly on data reported in the anthropological literature which was reviewed by Frances Barnes in her article "The Biology of Pre-Neolithic Man" (1970).)

The biology of primeval mankind

Nutrition and feeding habits:

The energy required for growth, muscular work and basal metabolism was obtained from food of both animal and plant origin. The relative proportions of meat and vegetable matter varied according to circumstances, but usually the greater part of the diet was, by weight, of plant origin. Most of the food was brought back to the camp for eating.

Under favourable or typical conditions, activities aimed at the collection of food probably lasted for an average of two to three hours per day.

All hunting (except for small animals, such as lizards) was carried out by men, while the women, accompanied by some children, collected fruit, nuts, roots, etc. Men sometimes also took part in the gathering of vegetable food-stuffs.

Hunting was an occupation which was almost certainly enjoyed by the men. This sense of enjoyment in hunting may well be an innate characteristic of the species, of survival value in the evolutionary environment, and the product of natural selection. The same may well apply to food-gathering in women.

In the evolutionary environment, natural regulatory mechanisms operated to ensure that, under normal conditions, the intake of energy was directly related to the energy requirements of the body (Boyden, 1969). Much of the energy consumed was, in fact, utilised in the various activities associated with food-gathering itself, which involved periods of quite vigorous exercise each day.

Hunting combined the use of knowledge learned by experience and that transmitted by culture (relating to the environment, animal behaviour, etc.); it called for maximum use of intelligence; it involved the application of learned physical skills; it was characterised by co-operation between individuals; it was goal-directed (i.e. it had a built-in sense of immediate purpose); when successful it had a built-in sense of immediate reward - not only in the form of the satisfaction of hunger, but also in the form of praise and smiles from other members of the group, especially the women and children; it represented a challenge to the individual's mental and physical prowess and to his courage; it provided a daily outlet for aggressive feelings.

Rest and sleep:

In hunter-gatherer groups people tended to rest or sleep when they felt like it. Freedom to respond to feelings of sleepiness by going to sleep resulted in a polyphasic sleeping pattern, which typically included at least one nap during the daylight hours, usually around midday or slightly after.

Sexual behaviour:

Very little is known of the details of sexual behaviour in primeval societies.

Creative activity:

(a) Typically, most individuals in hunter-gatherer groups spent part of each day making and shaping things. This activity had the following characteristics: (i) it involved the exercise of learned manual skills; (ii) it was goal-directed, i.e. it had a built-in sense of purpose, as in the manufacture of weapons for hunting or defence, or utensils for preparing food or of ornaments to decorate the individual. It is noteworthy that the finished article frequently appears to be the product of more workmanship and effort than was necessary to render it functional, suggesting that some satisfaction may have been derived from bestowing an extra aesthetic quality on the object.

(b) Some individuals in the hunter-gatherer groups specialised in such creative activities as story-telling or music making.

Social interaction:

Hunter-gatherer bands varied in size according to the nature of the terrain, and other factors. A typical band consisted of 30-40 individuals, including children. Bands might split up, come together again and exchange numbers according to circumstances (e.g. distribution of food supply, personality factors, etc.). Flexibility seems to have been the rule.

Much time was spent in conversation, discussing matters of mutual interest, exchanging information on aspects of the environment, sharing problems and anxieties, joking and story-telling.

Children were shown much affection by adults, and the attitudes towards them, especially small children, were generally permissive. While the parents, especially the mother, were expected to take main responsibility for their children, there was a good deal of communal co-operation with respect to the minding of children. For example, small children might be left with elderly members of the group at the camp when their mothers went off to gather food, and sometimes one woman would take care of several children other than her own for a considerable period.

In primeval societies there was little evidence of sharp "generation gaps", although the onset of puberty was often recognised as an important event. Young children tended to learn skills and to acquire knowledge from their older siblings or friends, who in turn learned from their older siblings and friends, and so on. Elderly people were, under favourable environmental conditions, treated with respect.

Strangers and strange groups were regarded with suspicion. However, open hostility between groups, involving physical violence, is not a feature of extant hunter-gatherer societies although this is not to say that such hostility never occurred in primeval times.

Visual environment:

It was an environment full of interest to the observer; it was characterised by a certain functional harmony, and it was dynamic in the sense that significant changes were occurring in it from day to day or from season to season (i.e. it was never completely static - as, for example, a room in a modern home may be). Another point of relevance is that, if there are genetically-determined components to a man's aesthetic sense (and I strongly suspect that there are), then these were determined through natural selection by pressures associated with the visual environment of the evolutionary period.


The mortality rates in primeval society were much higher than in modern Western society, and consequently the average age at death was much lower. The main factors contributing to ill-health and mortality were probably injury sustained in hunting and food-gathering (with subsequent infection of wounds) and attack by predators. Neither infectious disease due to bacteria and viruses nor malnutrition was a common cause of ill-health.

Biological determinants of optimal health

We have already noted that, if the conditions of life of an individual deviate from those to which the species has become genetically adapted through evolution, signs of phylogenetic maladjustment (physiological or behavioural) are likely to arise. With this principle of phylogenetic maladjustment in mind, I have utilised our knowledge of the conditions of life of mankind in his evolutionary environment to draw up a tentative list of some of the biological determinants of health of the human organism.

The list is not presented in any particular order, although I have tended to place the more easily definable "physicochemical" or "material" determinants of health first. There is inevitably overlap between some of the items on the list, particularly those concerned with behavioural and social aspects.

(1) An appropriate intake of calories neither in excess of, nor much less than the requirements for basal metabolism, growth (in children), and physical work performed.

(2) A well-balanced diet of a quality close to that of primeval mankind.

(3) Clean air. (note-The word "clean" in this list means "free of noxious agents and harmful products of technology".)

(4) Minimal contact with pathogenic microorganisms.

(5) Noise levels not much above or much below the range experienced in the natural environment.

(6) Minimal contact with noxious and chemical compounds.

(7) Absence of accessible physiologically and psychologically harmful drugs.

(8) A visual environment which is interesting, which has aesthetic integrity, and in which a certain amount of change meaningful to the observer is taking place.

(9) Daily periods of physical exercise, at times vigorous, and with clear goal-direction.

(10) Conditions which allow natural outlets for the sexual drive, and a reasonable balance between levels of sexual stimulation and sexual satisfaction.

(11) Opportunities to rest and sleep in response to the urge to do so (by night or day).

(12) Opportunities for spontaneous conversation with relatives and friends on matters of mutual concern and interest.

(13) Freedom to move at will from one social phase to another (i.e. from one small group to another or to and from a state of solitude).

(14) Opportunities for companionship and close friendship with other members of the in-group.

(15) Opportunities for mothers to leave young children on occasion in the care of others.

(16) Opportunities for frequent and unimpaired expressions of the universal behavioural tendencies of the species (e.g. tendency to seek approval, or esteem within the in-group, and to avoid ridicule, to compete with peers, to explore the unknown). (note-This whole question of the innate behavioural characteristics of the species is of critical significance in relation to the major problems facing human society. It is also a highly controversial subject [see Boyden, 1973]).

(17) Opportunities and incentives for personal creative behaviour preferably with clear goal-direction, involving especially the exercise of learned manual skills, or in story-telling, music making, etc.

(18) A considerable degree of emotional involvement and a sense of immediate purpose in the main activities of the day.

(19) Conditions which result in full awareness of a role of oneself in the in-group or community.

(20) A considerable degree of variety in daily experience and activity.

(21) General opportunities for self-expression and self-fulfillment.

In essence, then, this is a list both of the main features of the conditions of life of Homo sapiens in the evolutionary environment of the species and of postulated biological determinants of optimal health in modern society.

Since it is clear that many of the conditions listed are not features of the pattern of life of the modern city dweller (note-The range of deviation in the conditions of life from the primeval pattern is extensive. A fairly comprehensive list of these deviations has been presented elsewhere (Boyden, 1972c.)), the question arises, in the case of each deviation that can be recognised from the evolutionary pattern, whether or not the change is giving rise to phylogenetic maladjustment in any form, physiological or behavioural, severe or mild. (note-Lest I be accused too readily of Rousseauian romanticism, let me hasten to repeat that neither attack by predators nor serious injury sustained in hunting, which were common causes of death and suffering in the primeval situation, are features of life in modern urban communities, and that consequently the average age at death is much higher now than it was then. Moreover, infection of the tissues with microorganisms is far less likely to result in death today than was the case in the primeval environment.)

In some instances, of course, the connection has already been clearly established between certain environmental changes associated with civilisation and certain forms of phylogenetic maladjustment. For example, crowding in cities, in the absence of appropriate cultural adaptation involving the introduction of new standards of hygiene to suit the new conditions, results in alterations in host-parasite* relationships so that item number four on our list - minimal contact with pathogenic microorganisms - is not satisfied and severe signs of phylogenetic maladjustment are manifest in the form of various contagious diseases.
(*The term parasite is used here in the general sense to include bacteria, fungi, viruses, protozoa, helminths, etc. potentially parasitic in the human species.)

Implications for modern society

While the modern urban environment in the developed countries satisfies the survival determinants for the average individual, it may not do so well with respect to the well-being determinants. The average man and woman are not, for example, involved each day, as were their ancestors, in personal creative activity; their levels of physical exercise are much diminished; their opportunities for resolving personal tensions by the reaction of mutual avoidance are restricted; and society imposes on them a monophasic sleeping pattern. Even more importantly- the average urban dweller is little involved emotionally in most of his daily activities. "The shining eye, ease of movement and quick heart beat which reflect the adaptation to enjoyable or emotionally inspired activity" (Minc, 1970) are rare sights in the modern city. This culturally-imposed divorce of the functions of the cerebral cortex and the limbic system deprive the individual of a sense of immediate purpose and of enjoyment in his daily routine. Moreover, it has been argued on neurohormonal grounds that this change may result in various forms of phylogenetic maladjustment, including cardiovascular disease and "minor morbid conditions which are so common today: headaches, lassitude, irritability, depression, and possibly aggression" (Minc, 1970).

The arguments put forward here represent a development of the idea that an evolutionary approach to the study of mankind in the modern world can help us to view the human situation, and both the advantages and disadvantages of civilisation and technology, in meaningful perspective. By way of conclusion, it would be useful, I feel, to attempt a brief summary of the impact of technology on the biology of the human species:

(1) Modern technological society, by the protection it provides against the primeval causes of death, by making greatly increased quantities of food available and, more recently, by the protection it has afforded in more developed areas against the great lethal diseases of civilisation, has increased to an extraordinary degree the number of specimens of the human species that can exist on earth at any given point of time and also their average life-span.

(2) Technology has increased to a remarkable degree the impact of the human species on the biosphere. An idea of the scale of human activity can be gained from the fact that, as a result both of the massive population increase and of the even more explosive spread and development of technology, the human species is now utilising energy at about the same rate as all the other land animals and plants put together (Boyden, 1972c). The rate of energy utilisation, which is a fair measure of the impact of human society on the total environment, is increasing exponentially at about double the rate of population increase. (note-Part of the dilemma lies in the fact that ever-expanding industry and advancing technology, which are supposed to lead to an increased "standard of living", represent, in effect, a frantic effort on the part of society to continue to provide very simple and basic human needs (e.g. an adequate and balanced diet and freedom from pestilence). Ever-accelerating technological advance seems to be necessary in order to maintain the status quo in terms of the essential requirements of the human organism. A sophisticated food technology and an efficient transport and distribution system are essential if people in the great Western cities are to receive an adequate and balanced diet. The two automobiles per nuclear family, now common in some sections of Western society, provide the family with (a) some prestige, (b) the means by which the adult male can reach his place of work, (c) the means by which the female can visit relatives and friends and procure provisions, (d) the means by which the children can participate in group activities, (e) the means by which they can all visit the natural environment. It was possible for every one of these human "needs" to be adequately satisfied in bygone societies, even before the invention of the wheel, let alone the internal combustion engine.) It is clear that, if civilisation is to survive, a state of equilibrium must be restored to the biosphere.

The solution to the problem, if there is one, must surely lie, not in further mindless intensification of technological and industrial effort, with increasing GNP as the sole objective but rather in a re-organisation of society based on increased emphasis on the quality of individual lives and involving some fundamental changes in our value systems. The materialistic objectives of the Western world have been questioned by moralisers and philosophers for a long while, but the growing awareness of the threats to human survival in the ecological situation now adds a practical flavour to the problem. Questions such as "Where are we?", "Where are we going?", "Where do we want to go?", and "What is progress?" are taking on a new and urgent significance. It has been a theme of this paper that human biology can help us see the relevance of these questions and can also contribute usefully to our attempts to answer them.


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