29 Adaptation to ecological stress-nutrition and solar radiation

Imkongtenla Pongen and Meenal Dhall

Contents:

Introduction

1. Biological and cultural evolutionary aspects of human nutrition

1.1 The hunting phase of man

1.2 The agricultural revolution and sequelae

2. The World’s food supply and related problems of quality and quantity

3. Effects of nutritional inadequacies upon health and quality of life

3.1 Fetal retardation

3.2 Infant malnutrition

3.3 Child malnutrition

3.4 Retarded growth and development in younger children (1-5 years)

3.5 Later childhood and adolescence

3.6 Morphology of adult body

4. Effects of overnutrition :Growth adult morphology and health of economically more privileged people

5. Adaptation to solar radiation

5.1 Functional and genetic adaptation

5.2 Sunburn and toxemia

Summary

Learning Objectives:

1. Describe the biological and cultural evolutionary aspects of human nutrition.

2. Elucidate the world’s food supply and related problems.

3. Explain the effects of nutritional inadequacies upon health and quality of life.

4. Explain the effects of overnutrition on health.

5. Describe the different adaptive features of the skin to solar radiation-functional and genetic adaptation.

Introduction

Human nutrition is an important environmental factor affecting the evolution and variability of humans. In nutritional terns of human adaptation, it is necessary to attain metabolic balance which could be accomplished by physiology of the human body besides cultural influence and this is reflected in the morphology. These morphological and physiological adjustments are under polygenic control.

Boas (1911) strongly suggest that postnatal growth and adult morphology were greatly influenced by diet. The modern biologists have considered four broad topics with respect to man’s adaptation to nutrition: the biological and cultural aspect of nutrition, the world’s food supply and its related problems, the effects of nutritional inadequacies upon health and the effect of overnutrition upon growth and health.

1. Biological and cultural evolutionary aspects of human nutrition

1.1 The hunting phase of man

Man as a hunter with strong dependence upon animal foods dates back to one million years. There was regional and temporal differences in the amount of animal and vegetable foods consumed during the man’s hunting phase. Butzer (1971) states that vegetable foods were more apparent in many sites where Homo erectus was living in the Old world. However in case of the modern hunter-gatherers, only in few cases (eg: Eskimos) , animal hunting was as productive as gathering of seeds, fruits, etc. Man’s long phase of hunting has brought animal food into his diet which changed both his metabolically controlled growth and his social life. The flesh of animals is packed with nutrients and it appears to be stored by smoking and drying during the Mousterian and Upper Paleolithic period. These well adapted hunters were repleted with famine and starvation. Under this famine mode of life, they had the ability to efficiently metabolize food and build bodily reserves of energy. This lead to favorable genotypes under severe deprivation of food: those determining hypercholesterolemia, the thrifty genotypes with efficient metabolism which may lead to diabetes mellitus in industrialized places, the related genotypes of “strange bedfellows” diabetes and obesity predisposing to greater accumulation of fat. Even with careful dieting, the ontogenetic foundation of fat does not disappear which is laid in perinatal and early childhood. This early accumulation of fat may be beneficial to the young in the hunting societies and may constitute an aspect of programing of genes. All of the above cited genotypes become disadvantageous in a high calorie, high carbohydrate and physically inactive life.

Dependence upon animal food for millions of years would have altered the amount and the kind of protein requirements of man. Infant and childhood protein requirement is four times per unit body weight as adult requirements. The amino acid balance of animal protein provides the ideal utilization. Protein malnutrition in man is a peculiar genetic deficiency. For proteins from vegetables, Dubos (1965) states that those derived from green leaves and some microbial species contain essential amino acids but they could not be easily digested. But protein from seeds and other storage plants lack in one or many of the eight essential amino acids. For protein atleast it is clear that modern man is not well adapted to simply exclusive vegetable diet.

1.2 The agricultural revolution and sequelae

Domestication of plants and animals dates back some ten thousand years in Southeast Asia and as early as nine thousand years in Mesoamerica. In most of the places in the world, transition to a vegetable diet was slow. The need for lands for agriculture squeeze out the pasture for domestication of animals. From 9000-6000 years B.P., the plant food increased from 30 to 60 %.domestication of bean lead to increase in contribution of plant food to diet by about 6000 years B.P. In less than 9000 years (450 generations), the contribution of animal foods in the diet decreased from 70 to 5%. Reduction of animal protein and increased dependence upon plant crops such as rice, wheat and millet was observed down through time. With increase in technological methods, these crops are been bred for higher yield and has been exposed to constant milling and bleaching at the expense of nutrients.

Villages becomes towns and towns become cities and man’s self-contamination has brought in the Pandora’s Box of infectious, “crowd type” diseases. Increase in restrictive diets have made the nutritional diseases a threat to quality of life of humans as that of the infectious diseases in the underdeveloped four-fifths of the world’s nations . Both infectious and nutritional diseases act synergistically to increase human misery. Without good well controlled studies, it is difficult to separate nutritional and pathogenic agents as the main cause of deaths. However Dumont and Rosier (1969) have estimated that out of the sixty million deaths in the world each year, ten to twenty million deaths are attributable to dietary deprivation.

2. The World’s food supply and related problems of quality and quantity

Infectious disease has been the strongest selective force since the Agricultural revolution as suggested by Haldane in 1932. The FAO Third World Survey conducted in 1963 and others might have underestimated the international problem of food and might have represented only a dip of the iceberg. The data for such estimates are very limited but the quoted FAO figure is that atleast 20% of the world’s population are malnourished calorically and 60% are malnourished in one or more essential nutrient. A FAO/WHO Expert Group in 1965 estimated that one-quarter and one-third people of the underdeveloped nations of the world have deficiency of protein in their diet with intake of protein as the single most significant indicator of adequacy of nutrients.

There was 2% annual increase in the world’s population as against 1% increase in annual supply of food till 1970. But world harvest exceeded that of 1969 by 2% including a 5% increase in the Far East. The increase in harvest of food is due to improved seed and agricultural technology brought about by the Green Revolution. But this progress is narrow in the underdeveloped four fifths of the world. By mid 1970’s droughts and famine prevailed and there was widespread starvation all over the world.

3. Effects of nutritional inadequacies upon health and quality of life

3.1 Fetal retardation

In periods of famine in most cultures of the world, there is ample evidence of history of mother’s nutrition ,including her early life as well as the nutrition she gets from food during pregnancy have strong influence for the growth and development of her fetus. Those mothers who have small body size due to deprivation of nutrients have poorer reproductive histories than those who have larger body size with better nutritional status. The former have more premature births, more birth defects, higher premature mortality and more difficult labor. In a study in New York, the late stillborn of the poor mothers had small weights for the spleen, liver, thymus, subcutaneous fat and adrenals.

3.2 Infant malnutrition

It is well established that the size of body of adults and newborn indicate clear socioeconomic gradients in all ethnicity. Low birth weight and neonatal mortality are more rampant in underdeveloped than developed nations. Lactation is the period where milk production of well nourished mothers are adequate for the proper growth and development of their babies within the first six months after birth. Lactation is halved in quantity due to inadequate maternal nutrition, especially protein, which contributes to slow in growth and even loss in weight within the first six months. The shift to often contaminated diet that contains high-carbohydrate, low-protein solid foods either before or upon weaning is a critical period. In this period, protein deficiency disease such as kwashiorkor or marasmus develops. Full clinical manifestations of such diseases occur when mismanaged nursing bottle substitutes the breast feeding. Early mortality increases with birth order in families with limited resources of food. Studies in few tropical and subtropical nations estimates that during the first five years of life, about one-half of all liveborn die of undernutrition and its sequelae.

3.3 Child malnutrition

A child in poverty is subjected to even more hazardous age-grade if he/she survives the first year of life. 1-4 year old rate of death provides a single indicator of the nutritional status of a country. Secotrant (second year plus transitional) identifies the critical second year of life when a child is displaced at the brease due to arrival of a new sibling in the family. This neologism is been given by Jelliffe in 1969. Infectious diseases (eg: diarheas) act synergistically with maladaptive food habits, poor nutrition and psychic deprivation to make the rate of child mortality and morbidity higher. The universal responses to inadequate nutrition and infectious diseases are retarded growth and development because the nutritional programming under deprived conditions override the genetic control exercised over them. This retardation patterns include small size of the body, low bone densities, certain degree of mental and emotional handicap and retarded skeletal maturation. More likely the permanency of brain damage due to protein malnutrition may happen earlier the nutritional deprivation.

3.4 Retarded growth and development in younger children (1-5 years)

The parts of the body that are most affected are those parts which grows more rapidly at the time. Full catch up growth, upon rescue occurs after war or other catastrophes in developed countries but such catch up little occurs in underdeveloped nations where such dietary rescue is rare. For instance in Guatemala, lower-class rural children take longer time to catch up than better-off urban children.In such nations, there is never sufficient food to comprise dietary rescue during growth and such slow physical development leads to adults with small body size. Sexual maturity is also associated with under nutrition-the later the menarche the smaller the people- which is in fact referred to as the Malcolm’s Law. Even though there is still an unanswered question regarding the availability of mineral in plant foods, deficiency of zinc in poor rural children who were exclusively on vegetable diets appeared to be have retarded growth as well as reduced sexual maturation.

3.5 Later childhood and adolescence

There is further evidence from Peru that dietary rescue has a reduced effect on 7-12 year old boys than on adolescent 13- to 18 year olds. The reason for this incomplete catch up in younger boys could be due to low socio-economic status or all that goes within their households or that they might have faced restricted growth in earlier life caused by long term genetic selection against rapid growth. Frisancho et al. (1970) revealed an age related pattern of retardation where pre-adolescent children showed retardation in height 10% less below US standards but an over 30% delay in skeletal maturation. Here, pubertal growth spurt was not only milder but was also delayed in poverty dominated nations and the timing is closely associated to intake of calories.

3.6 Morphology of adult body

Since the last twenty years ,it is also clear that the size of the adult body is reduced on an average with increase in temperature. This gives the evidence that Bergmann’s rule developed for homeotherms is also operating. But in recent times, it appears that this body size-temperature association is due less to Bergman’s principle than to the lower food-producing potential of most hotter regions in the world. Frisch and Revelle (1969) have demonstrated that adult body size is strongly mediated by nutrition through the steep regressions of mean adult male body weights or mean intake of calories for six Asian and six Latin American countries. Malhotra in 1966 also give confirmatory evidence that the mean height of males increased with intake of protein and calorie from the south to the central and then northern parts of India. There were differences in proportions of body also, better well-fed and taller people had relatively longer leg.

4. Effects of overnutrition: Growth adult morphology and health of economically more privileged people

Indeed most of the nations in the world are underfed , however the better-off socio-economic strata of the developed nations are overnourished. The “over-developed” nations are facing the infantile obesity syndrome vis-à-vis the protein-calorie malnutrition faced by underdeveloped nations. According to Biological Freudianism concept of Dubos (1968), over nourished individuals are programmed early in life for overeating. Children who are overweight become overweight adults. Genetic programming for metabolic efficiency that is adaptive to man as a hunter have become maladaptive in the overfed, physically inactive urban lifestyle of developed nations. Lower socio-economic classes in most developed countries show higher incidences of obesity than the upper ones due to their intake of higher carbohydrate diets. Similarly as obese babies are lower in resistance to infectious disease, obese adults are more prone to metabolic diseases especially cardiovascular diseases. Obesity also has a “strange bedfellow” to diabetes. Risks of premature mortality and morbidity from overeating and physical inactivity are multifactorial and complex, and it also involves hypertension, hypercholesterolemia, cigarette smoking, overuse of alcohol and psychic stressing.

5. Adaptation to solar radiation

5.1 Functional and genetic adaptation

Functional adaptation refers to the biological changes that occur during the lifetime of an individual .It is also known as developmental adaptations or acclimatization.

One trait that plays a pivotal role in resistance to solar radiation is skin colour. Ladell (1957) has said that the darker the colour of the skin, the greater is the heat absorption. Skin colour of humans varies from a very dark brown among Australian Aborigines, Melanesians and fe Africans to a yellowish pink among North Europeans. The colour of the skin is due to presence of a pigment known as melanin, which is located in the epidermis of the skin and is controlled by six genes. Two forms of melanin are produced, viz; pheeomelanin-red to yellow in colour and eumelanin-dark brown to black. Individuals differ in the size and number of melanin. Number and size of the particles of melanin are more important in determining the colour of the skin than the percentages of the different types of melanin. In lighter skinned people, colour is affected by the red cells in the blood that is close to the skin and is also less affected by the presence of subcutaneous fat and carotene( a reddish-orange pigment in the skin).

Mechanism of melanin: Melanin is formed at the base of the epidermis by the cells known as melanocytes which are photosensitive and detect ultraviolet radiation from the sun and other sources of energy. In response to the radiation, the melanocytes produce melanin within few hours.

People with darker skin are selected by nature in tropical latitudes in non forested regions where solar radiation is most intense. Melanin acts as a protective shield against solar radiation which helps in preventing sunburn damage that could result in changes in DNA and later skin cancers (melanoma). Approximately 54,000 people get this skin cancer every year with an estimated death of nearly 8000 in the US European Americans have a 10 times higher risk of developing skin cancer than African Americans.

Solar radiation usually increases in summer and decreases during winter. Tanning is an acclimatization to this seasonal change. It is an increase in the size and number of melanin particles due to the stimulation of the radiation of the ultra-violet rays. It is mostly seen on light complexioned people. However dark complexioned people also tan after prolonged exposure to sun. Some of the Northwest Europeans have lost their ability to tan due to natural selection, their skin burns and peels instead which is due to defective production of a skin protein Mc1r(melanocortin-1 receptor) that is required for formation of melanin. Those kind of people and those who are albinos are most susceptible to develop skin cancer. But at the same time it would be harmful if melanin acted as complete shield because a certain amount of short wave of ultra-violet radiation is required to penetrate the skin for synthesis of 90% vitamin D. 10% of vitamin D comes from dietary food .this vitamin is required in the intestines to absorb calcium and phosphorus for normal functioning and repair of bones. Recent research have suggested that vitamin D help in preventing a wide range of cancers and defend our bodies from infection of bacteria and viruses. However too much penetration of ultra-violet radiation may lead to breakdown of folate in our body resulting in anemia. Pregnant women deficient in folate are at an increased risk of neural birth defects and miscarriages. People living in far northern latitudes have an advantage of their skin with little pigmentation where ultra-violet radiation is weak. In such habitats, very dark skin people have deficiency of producing vitamin D resulting rickets, osteoporosis and higher incidence of pelvic deformities. The Inuits of the Subarctic are an exception because they have heavy pigmentation on their skin inspite of living in the far North. They made up the disadvantage of less production of vitamin D by eating fish and sea mammal.

Women mostly produce 3-4% less melanin than men due to the fact that women requires more calcium during reproductive years, preference of mate selection and other cultural practices.

Negros sweat more than the Europeans because the former are less tolerant of heat due to greater absorption of heat by dark skinned people Skin reflectance is the measurement of the ultra-violet radiation exposure. It is the amount of light that is reflected from the skin and is used to assess the colour of the skin. Ladell (1957) have noted that an European reflects three times more of solar radiation than a Negro even though both of them absorb same amount of low temperature radiation from the ground. Weiner at al (1964) found that skin of Negroid people absorbs more than twice as much light as the Europeans .The light absorbed is converted by the heat into a combined heat which when added to the combined metabolic heat and heat absorbed from the environment increases the excess total heat that has to be discharged by radiation, convection and evaporation of sweat. Thus black skin in unshaded areas increases heat stress, at the same time blocks the harmful direct ultra-violet radiation. In other words, a black skinned person is heated more but burned less than a white skinned person when exposed to solar radiation. Similarly, a blond person is burnt more severely but heated much less than a dark skinned person. However most white skinned people achieve considerable protection by tanning to a degree which blocks the harmful UV rays without significantly increasing the absorption of heat. This reflects an ideal condition of adaptation and natural selection.

5.2 Sunburn and toxemia

Malmejac in 1960 found out that when the temperature of the skin is raised above 41̊ C, symptoms of toxemia occurs which is caused by sudden release of histamines (four times increase than normal) by the overheated skin. Increase in release of histamines with increase in skin temperature lead to sharp drop in blood pressure. Vasodilation are enhanced by increase in capillary permeability which then produces edema.

Summary

Man’s years of hunting has narrowed his nutritional requirements especially the amino acid balance of animal proteins. Shift to vegetable food accelerated by the Agricultural Revolution some ten thousand years has placed him in a dietary dilemma. The amino acid content of animal protein is close to FAO optimal pattern but the amino acid of seeds and tuber proteins are deficient in one or many forms of amino acids. Human societies have concentrated one some major crops, viz; rice, wheat, millet and corn and have developed maladaptive habits concerning those staple crops. Adults can get their enough dose of protein from plants if they eat it in large quantities but the enhanced needs of it during infancy, gestation, lactation and childhood may not suffice their requirements of amino acids. Moreover, proteins from plants bind more easily making them less available for absorption.

Although the Agricultural Revolution has transformed a hunter-gatherer life to a settled life,growth of population and progress in technology,in both epidemiological and nutritional sense it has brought in its own share of demerits as well. Villages becomes towns and towns become cities and man’s self-contamination has brought in the Pandora’s Box of infectious, “crowd type” diseases. Dumont and Rosier (1969) have estimated that out of the sixty million deaths in the world each year, ten to twenty million deaths are attributable to dietary deprivation.

The FAO Third World Survey conducted in 1963 and others might have underestimated the international problem of food and might have represented only a dip of the iceberg. Atleast 20% of the world’s population are malnourished calorically and 60% are malnourished in one or more essential nutrient. A FAO/WHO Expert Group in 1965 estimated that one-quarter and one-third people of the underdeveloped nations of the world have deficiency of protein in their diet.

There was 2% annual increase in the world’s population as against 1% increase in annual supply of food till 1970. But world harvest exceeded that of 1969 by 2% including a 5% increase in the Far East, brought about by the Green Revolution. By mid 1970’s droughts and famine prevailed and there was widespread starvation all over the world.

In periods of famine, in most cultures of the world, there is ample evidence of history of mother’s nutrition ,including her early life as well as the nutrition she gets from food during pregnancy have strong influence for the growth and development of her fetus. Those mothers who have small body size due to deprivation of nutrients have poorer reproductive histories than those who have larger body size with better nutritional status.

Low birth weight and neonatal mortality are more rampant in underdeveloped than developed nations. Lactation is halved in quantity due to inadequate maternal nutrition, especially protein, which contributes to slow in growth and even loss in weight within the first six months. In this critical period, protein deficiency disease such as kwashiorkor or marasmus develops.

A child in poverty is subjected to even more hazardous age-grade if he/she survives the first year of life. 1-4 year old rate of death provides a single indicator of the nutritional status of a country. Infectious diseases (eg: diarheas) act synergistically with maladaptive food habits, poor nutrition and psychic deprivation to make the rate of child mortality and morbidity higher. The universal responses to inadequate nutrition and infectious diseases are retarded growth and development because the nutritional programming under deprived conditions override the genetic control exercised over them.

Since the last twenty years, it is also clear that the size of the adult body is reduced on an average with increase in temperature. Frisch and Revelle (1969) have demonstrated that adult body size is strongly mediated by nutrition through the steep regressions of mean adult male body weights or mean intake of calories for six Asian and six Latin American countries.

Indeed most of the nations in the world are underfed , however the better-off socio-economic starta of the developed nations are overnourished. The “over-developed” nations are facing the infantile obesity syndrome vis-à-vis the protein-calorie malnutrition faced by underdeveloped nations.

One trait that plays a pivotal role in resistance to solar radiation is skin colour. The darker the colour of the skin, the greater is the heat absorption. Number and size of the particles of melanin are more important in determining the colour of the skin than the percentages of the different types of melanin. Melanin is formed at the base of the epidermis by the cells known as melanocytes which are photosensitive and detect ultraviolet radiation from the sun and other sources of energy.

Tanning is an acclimatization to this seasonal change. It is an increase in the size and number of melanin particles due to the stimulation of the radiation of the ultra-violet rays. It is mostly seen on light complexioned people. However dark complexioned people also tan after prolonged exposure to sun.

Women mostly produce 3-4% less melanin than men due to the fact that women requires more calcium during reproductive years, preference of mate selection and other cultural practices. A black skinned person is heated more but burned less than a white skinned person when exposed to solar radiation. Similarly, a blond person is burnt more severely but heated much less than a dark skinned person.

When the temperature of the skin is raised above 41̊ C, symptoms of toxemia such as low blood pressure and edema occurs which is caused by sudden release of histamines (four times increase than the normal) by the overheated skin.

Glossary

Adaptation – The process of physiological, genetic and biochemical modification to a particular environment and/or stress in order to survive and reproduce.

Ecological stress – Constraints of the physical , biological and chemical productivity of species and on the development of ecosystem.

Functional adaptation – Also known as developmental adaptations or acclimatization, it refers to the biological changes that occur during the lifetime of an individual .

Melanin – A pigment which is responsible for giving colour present on the epidermis of the skin controlled by six genes .

Over-nutrition – A condition when there is excessive intake of food or nutrients.

Skin reflectance – Measurement of the ultra-violet radiation exposure.

Solar radiation – Energy radiated from sun in the form of electromagnetic waves, visible light, UV light and infrared radiation.

Stress – Any factor that interferes with the normal limits of functioning of an organism.

Under-nutrition– A form of malnutrition when there is inadequate food consumption or faulty assimilation.

Vasodilation – The widening of blood vessels that results from relaxation of the muscular walls of the vessels.

Did you know?

1)Out of the sixty million deaths in the world each year, ten to twenty million deaths are attributable to dietary deprivation as estimated by Dumont and Rosier (1969) .

2) Ever since the Agricultural revolution ,infectious disease has been the strongest selective force as suggested by Haldane in 1932.

Interesting facts

1)FAO figure that atleast 20% of the world’s population are malnourished calorically and 60% are malnourished in one or more essential nutrient.

2) The colour of the skin is due to presence of a pigment known as melanin, which is located in the epidermis of the skin and is controlled by six genes.Two forms of melanin are produced,viz., pheeomelanin-red to yellow in colour and eumelanin-dark brown to black. Individuals differ in the size and number of melanin.

Points to ponder:

Some of the Northwest Europeans have lost their ability to tan due to natural selection, their skin burns and peels instead which is due to defective production of a skin protein Mc1r(melanocortin-1 receptor) that is required for formation of melanin. Those kind of people and those who are albinos are most susceptible to develop skin cancer. But at the same time it would be harmful if melanin acted as complete shield because a certain amount of short wave of ultra-violet radiation is required to penetrate the skin for synthesis of 90% vitamin D.

References

Dalmont A (Ed.). (1975). Physiological Anthropology. New York, NY: Oxford University Press.

http://anthro.palomar.edu/adapt/adapt_4.htm

Suggested Readings:

http://www.dnva.no/geomed/solarpdf/Nr_10_Hessen.pdf

http://www.medical-hypotheses.com/article/S0306-9877(06)00182-4/fulltext