The Evolution Of Human Nutrition Biology Essay

During a lifetime, a human being will eat thousands of pounds of food. The body will use this food to grow, to repair damaged tissue, and to maintain organs such as the brain and heart. Some of these foods will be enjoyable to eat because they are perceived to look appetizing and taste delicious. Other foods may not be enjoyable to eat, but will be consumed anyway because they are “good for the body or the spirit.” Biochemically, the body does not distinguish between foods that are liked or disliked, for the human body does not use food, rather the body requires the biological nutrients contained in food. Biology, however, is not the entire story of human nutrition. Cultural variables, such as the type of food eaten, its manner of preparation, and the social context in which it is consumed, often determine the efficacy of that food in meeting human needs for health and well-being. It is the purpose of the chapter to explore the evolution of some of the biological and cultural requirements of human nutrition. Although at times the biology and culture of nutrition will be treated separately, the major theme of this chapter is to view human nutrition holistically as a biocultural phenomenon.

The Conception of the People of Corn

It was night, and the gods sat thinking in the darkness. Among them were the Bearer, Begetter, the Makers, Modelers named Tepeu Gucumatz, the Sovereign Plumed Serpent. Twice before they had tried to create a human being to be servant to the gods. One time the humans were made of clay and the other time of wood; but on both occasions the creatures so formed were stupid, without any intellect and without spirit. So, they were destroyed. As the dawn approached the gods thought, “Morning has come for humankind, for the people of the face of the earth.” Their great wisdom was revealed in the clear light; they discovered what was needed for human flesh- white corn and yellow corn. Four animals brought the food: fox, coyote, parrot. And crow. The animals showed the way to the citadel named Broken Place, Bitter Water Place. Here was a paradise filled with white and yellow corn and all the varieties of fruits and vegetables. including pataxte and cacao. The white and yellow corn were given to Xmucane. the divine Grandmother of the gods, and she ground the corn nine times. She washed the ground corn from her hands with water and this mixture made grease. The corn was used to make human flesh, the water made human blood, and the grease made human fat. From these staple foods were born the strength and vigor of the new beings. (From the Popol Vuh, the Maya book of the dawn of life and the glories of gods and kings [compiled from the translations of Tedlock 1985 and Figueros. 1986].)

The domestication of maize, or corn, and other plants occurred in Mesoamerica about 7000 B.P. By 3000 B.P. maize-based agricultural societies were established and these developed into the state-level, hierarchical societies of the Olmec and, eventually, the Maya. The central place of maize as the staple food in Maya society is emphasized in the creation story. People are corn, in both the literary and literal sense. Today, the living Maya people of Guatemala depend on maize for 80 percent of their energy intake. It is likely that the ancient Maya also consumed a large portion of their calories from maize, or more correctly from maize-based foods. Very little maize is eaten in Guatemala today. Instead people eat tortillas, tamalitos, tamales, tacos, enchiladas, atoles (a beverage), and many other foods and drinks made from masa harina. Masa harina is a flour made from maize that has been dried, ground, and processed by boiling in lime water (Figure 6.1). Some of the “tortilla chips” sold in American supermarkets may be made from a flour like mass harinha, but most brands are made from corn meal, which is ground maize without any processing. The difference is vitally important in terms of nutrition and health, for without the processing, a maize-based diet leads to death from pellagra. Later in this chapter the biochemical and nutritional properties of masa harina and the cause of pellagra are explained in greater detail.

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The Maya, ancient and modern, do not live by tortillas alone. At Broken Place, Bitter Water Place (a supernatural site located inside a mountain), all varieties of fruits and vegetables were found and given to people. A visit to any Maya marketplace today in Guatemala or southern Mexico shows that dozens of species of fruits, vegetables, and dried mushrooms are sold, along with fresh and dried fish and meat. Archaeological and ethnographic field- work substantiates the diversity of foods in the Maya diet over the past 1,000 years or more (Saenz de Tejada 1988). Even pataxte and cacao were given to people by the gods (Figure 6.2). These are fruits from which cocoa and chocolate are made cochocoholics might recite an extra prayer of thanks to Sovereign Plumed Serpent before retiring tonighr). A chocolate and hot pepper beverage was a drink used in Maya religious ritual. and was usually reserved for the royal family or other people of high status. Thus, food is used not only to sustain the body, but also to demarcate social position and as part of religious behavior.

NUTRIENTS VERSUS FOOD

Nutritional biochemists have determined that there are 50 essential nutrients required for growth, maintenance, and the repair of the body. Essential nutrients are those substances that the body needs but cannot manufacture. These substances are divided into six classes: protein, carbohydrate, fat, vitamins, minerals, and water. Table 6.1 lists the essential nutrients in these categories. One way that nutrients are shown to be essential is via experiments with non-human animals. A young rat, pig, or monkey is fed a diet that includes all of the known nutrients except the one being tested. If the animal gets sick, stops growing, loses weight, or dies it usually means that the missing nutrient is essential for that animal. Such experiments do not prove that the same nutrient is needed for people. Some controlled experiments were done in the twentieth century with people, such as prisoners and residents of villages in underdeveloped nations. Since about 1980 these experiments have been considered unethical. Certain medical conditions deprive people of nutrients, and social, economic, and political conditions of life also deprive people of food and nutrients. By using these ” experiments of nature,” along with past research, it is possible to prove the necessity of the essential nutrients.

People do not usually intake essential nutrients directly as pure chemicals, rather we eat food. This was certainly true for all of our animal ancestors throughout evolutionary history. Human foods come from five of the six Kingdoms of living organisms: plants, animals, fungi (e.g., mushrooms), protists (e.g., species of algae referred to as “seaweed”), and eubacteria (e.g., bacteria used in fermented foods). These organisms present us with a dazzling array of colors, flavors. odors, textures, shapes, and sizes. The sixth Kingdom, archaebacteria. are not eaten directly, but are essential in the diet of other species that people do eat. Herbivores, for example, have archaebacteria in their guts to digest the plant cellulose.

Table 6.1 Essential Nutrients

Carboyhdrate

Glucose Fat or Lipid Linoleic acid Linolenic acid

Protein

Amino acids Leucine Isoleucine Lysine Methionine Phenylalanine Threonine

Tryptophan VaIine Histidine

Nonessential amino nitrogen

Minerals Iron Selenium Zinc Calcium Phosphorus Sodium Potassium

Sulfur Chlorine Magnesium Manganese Copper Cobalt Molybdenum

Iodine Chromium Vanadium Tin Nickel Silicon Boron Arsenic Fluorine

Vitamins

Fat-soluble: A (retinal) B (cholecalciferol) E (tocopherol) K

Water-soluble: Thiamin Riboflavin Niacin Biotin Folic acid

Vitamin B6, (pyridoxine) Vitamin B12, (cobalamin) Pantothenic acid

Vitamin C (ascorbic acid) Water

Source: Guthrie and Picciano 1995.

EATING A BALANCED DIET

How does a person know which foods to eat so that all of the essential nutrients are consumed in required amounts. ) Children learn what to eat because they are dependent on their parents, or other older individuals, to prepare their food. By tasting these foods, and watching older people prepare them, children acquire patterns of food preferences, including what should not be eaten, under what social conditions a food should be eaten, and the ways to prepare foods. Thus people learn what they like, for not all people eat all the same foods. For instance, some people in the United States eat chocolate covered ants, but most Americans do not think of insects as food.

In parts of Africa and South America, however, insects such as ants, termites, and beetle larva are food, in fact they are considered delicacies. Yanomamo Indians of southern Venezuela cultivate certain plants in which they know beetles will lay their eggs. The Yanomamo harvest the beetle larvae and eat them raw or roasted (Chagnon 1983). From a nutritional point of view insects are excellent sources of protein, fats, and some minerals. In fact, pound for pound, grasshoppers have more protein than cattle or hogs, yet this fact is unlikely to encourage the sale of “grasshopper nuggets” at fast-food outlets in the United States.

Every group of people has developed a cuisine: that is, an assortment of foods and a style of cooking that is unique to that culture. Some examples are Italian cooking, Chinese cooking, and Mexican cooking. Even Americans have a cuisine, including foods such as corn-on-the-cob and hamburgers. Despite the differences in specific foods, the cuisine of each human culture provides all of the essential nutrients. No one knows how cuisines developed to meet human biochemical requirements. Experiments with non-human animals and with people indicate that diets, or cuisines, are developed by learning to avoid foods that produce illness or feelings of malaise and seeking foods that promote feelings of well-being (Franken 1988:107).

One fascinating aspect of food preferences in different cultures is the way two or more foods are combined and eaten together to help assure nutritional adequacy. One example is complimentary protein consumption. Table 6.1 shows that there are nine amino acids (the building blocks of proteins) that are essential nutrients. There are 11 additional amino acids in nature that are needed for life but are not essential nutrients. Not all foods contain all nine essential amino acids, so we must eat several foods to get them all- the amino acids in some foods complementing those lacking in others. Cereal grains, such as wheat and rice, lack some of the amino acids that are found in beans, peas, milk, and cheeses. Conversely, beans, peas, milk, and cheeses lack the amino acids found in cereal grains. In the Middle East, many people eat wheat and cheese in the same dish. In Mexico, beans, tortillas, and rice are popular, while on the island of Jamaica peas and rice is the national favorite. In the United States, cereal (grains) and milk are complementary protein sources popular at the breakfast meal. The biochemistry of complementary protein foods has been discovered only recently, yet the cultural history of this food practice is ancient.

Each culture developed its own cuisine for many reasons. Not all foods grow in all countries, for instance maize originally comes from Central America and rice originally comes from Asia. But most food preferences cannot be so easily explained. The isolation of many human cultures, exploration and contact between cultures, ethnic identity, and social, economic, political, and religious status are some further explanations. Hindu culture, for example, specifies different cuisines for people of different castes. According to Burghardt’s (1990) analysis of Hindu dietary recommendation, not all castes can tolerate all foods. The intolerance is due to harmful reactions between the qualities of the food (such as animal meat) and the nature of the bodies of different caste members. Thus Hindu epistemology does not identify the universal set of essential nutrients recognized by Western bio-medical research. Many other unknown factors occurring throughout thousands of years of human history are also responsible for the development of culture-specific cuisines.

From the foregoing, two universal observations about human nutrition can be made: (1) All people have the same basic biological requirements for nutrients; and (2) Each culture has a unique cuisine that has the potential to satisfy these nutrient requirements. In addition some universal features of human food systems have been complied by Pelto and Pelto (1983):

1. People are extremely omnivorous. eating hundreds of different species of plants. animals, fungi, bacteria, and even algae.

2. People depend on systems of food transport from the place where foods are found or acquired to their place of consumption.

3. People make use of systems for food storage that protect the nutritional quality of foods from the time of their acquisition until the time of their consumption. That time period may last for months, even in premodern societies.

4. People expend great effort on food preparation. such as cooking, mixing, flavoring, and detoxifying natural ingredients, and depend on technology to do this preparation (e.g., the hand-axes and fire used by Homo erectus or the food processors and microwave ovens of Homo sapiens).

5. People share and exchange food regularly and have cultural rules that order such sharing and exchanges.

6. People have food taboos; that is, social proscriptions against the consumption of certain foods based on age, sex, state of health. religious beliefs, and other culturally defined reasons.

One final item must be included in this list of human food behavior.

7. People use foods for non-nutritional purposes, such as for medicine to cure or cause disease and as offerings in ritual or religious behavior (see the chapter by Etkin and Ross in this volume). In these contexts food may have some physiologic function (plants do contain active pharmaceutical compounds), but the foods also have symbolic meaning for the people using them.

Evidence from fossil and archaeological remains of human ancestors indicates that these universal features of human nutrition and food have been in existence for at least 35,000 years, and possibly more than 100,000 years. Yet, until this century, most foods were acquired locally. The most parsimonious way to account for these biological and cultural universals relating to food is to hypothesize that a common evolutionary history for all people shaped human nutritional requirements, food acquisition and processing systems, and food behavior. This is a hypothesis that can be verified or rejected by research.

SOURCES OF KNOWLEDGE

There are several kinds of data that may be considered in the study of the evolution of human nutrition. Archaeological and paleontological evidence provide the only direct data on what our ancestors ate and what effect diet may have had on our physical and behavioral evolution. However, studies of living primates and other mammals, living hunter/gatherer societies, and crosscultural comparisons of cuisines provide indirect evidence that is useful in reconstructing human nutritional history.

PRIMATE STUDIES

The living primates include prosimians. New World monkeys, Old World monkeys, Asian and African apes, and people. Fossil evidence indicates that all primates evolved from insectivorelike mammals that lived some 7.5 mil-lion years ago. The geological context of these fossils indicates that the general habitat was tropical forest. Primate ancestors may have been those insectivores that moved into the flowering trees of these tropical forests to exploit insects, and then the flowers, fruits, gums, and nectars of those trees (Cartmill 1974; Conroy 1990). The flowering plants and trees, called angiosperms, appear in the fossil record about 100 million years ago, and their appearance opened up new habitats and ecological niches that promoted the coevolution of other species, including the primates. The earliest primates of the Paleocence period (65-55 million years ago) exploited an insect-eating niche. Most species had jaws that moved in a scissorlike motion and teeth with pointed cusps, both features well suited for catching insects, by rapid mouth “snapping” and piercing their exoskeletons (the “crunchy” covering of the body) to extract internal tissues and fluids. By the late Paleocence many species show some dental traits indicating a mixed diet of insects, fruits, leaves, seeds, or gums. By about 55 million years ago primate fossils show changes in jaws and teeth toward those of living forms, with jaws adapted for greater power in biting and chewing. It seems that by that time most primates were eating fruits, leaves, and seeds as well as insects.

Thus, the general primate dietary pattern is ancient. That pattern is based on the ability to eat a wide variety of foods in order to meet nutritional requirements. Primate nutritional requirements are highly varied; the higher primates, including people, may be the animals with the longest list of essential nutrients. The reason for this may be our tropical origins. Today, tropical forests are characterized by having a high diversity of species, but a low density of any given species. There are thousands of species of tropical trees and at any one site there may be between 50 to 100 different species per hectare (Oates 1987), but only a few trees of the same species may be growing on that hectare. In contrast, temperate and high-altitude forests are often characterized by a few tree species, such as pine-oak forests, but large numbers of trees of those species. The diversity and density of animal species in tropical forests follows the pattern for plant life. There is no reason to expect that ancient tropical forests were different than modern tropical forests in terms of species diversity. Ancestral primates capable of eating a wide variety of foods would have had a veritable smorgasbord of choices, and judging by their descendants, the living primates, many food types were consumed.

The large number of essential nutrients required in the human diet, then, is likely a consequence of the tropical primate diet. With a wide variety of food resources, especially fruit, foliage, and insects, ancestral primates were able to obtain many vitamins, minerals, protein, carbohydrates, and fats from their diet. It is metabolically expensive, in terms of energy consumption, for an organism to manufacture its own nutrients (a process called autotrophism). Thus, through mutation and selection, those early primates that reduced autotrophism and shifted to a dependency on dietary intake to meet nutrient needs would have gained an energetic advantage, one that could be put to use, for instance, toward increasing reproduction. All mammals, for example, require vitamin C for maintenance and repair of body tissue, but only in some mammals, including all members of the primate order, is vitamin C (ascorbic acid) an essential nutrient. About 25 million years ago a mutation occurred in the metabolic pathway that produces vitamin C in primates ancestral to living monkeys, apes, and people. The glucose (carbohydrate energy) needed to convert biochemical precursors to ascorbic acid was released for use by other body systems (Scrimshaw and Young 1976).

The wide distribution of vitamin C sources in tropical environments and the ability of primates to utilize these sources assured that this nutrient could be supplied by the diet alone. Using published data, Harding (1981) divided naturally occurring tropical forest foods into eight categories and calculated the dietary frequency of each category for 131 species of primates from all families, excluding people (Table 6.2). The dietary frequency is defined as the percentage of those species surveyed “for which a given food category was listed in the diet” (p. 206). The data show that variety is the rule, and most species included seven of the eight food categories in their diets (“grasses and roots” was the category most often missing). The chimpanzee, our closest living primate relative, eats foods from all eight categories. It is worth noting at this point, that on a worldwide basis, living people eat more grasses, such as wheat and maize, and roots, such as potatoes and manioc, than any other foods listed in Table 6.2.

Table 6.2

Dietary Frequency and Major Diet Components of 131 Primate Species

Food category

Dietary frequency

Major component’

Fruit

90

45

Soil plant foods

79

9

Mature leaves

69

15

Invertebrates

65

23

Seeds

41

2

Hunted and scavenged

vertebrates

Tree parts

34

0

Grasses and roots

13

34

Source: Harding 1981.

Some selectivity in diet is seen in its major components, with fruits, invertebrates, and mature leaves being the most common items. Meat from vertebrates, either hunted or scavenged, and tree parts (e.g., bark, cambium) are not reported as major components for any non-human primate species. Thus it might be best to characterize primates not as omnivores, but as selective omnivores. There are several reasons for this selectivity. First, primates are, with few exceptions, diurnal and highly active. Second, primates have brains that are about four times larger, relative to body size, than the brains of other mammals. Third, primates have relatively long gestations prior to birth and are nursed on demand for a relatively long period after birth. Each of these traits places a high metabolic demand on an animal to maintain activity, to supply the brain with energy and oxygen (the human brain uses 20% of the body’s energy and oxygen), and to meet the nutritional needs of a mother primate and her fetus or infant.

Accordingly, primates must select foods that are dense in essential nutrients. Fruits and invertebrates are such foods; fruits are dense in carbohydrates, minerals and vitamins, and invertebrates are rich in fats and proteins (remember those grasshoppers!). Soft plant foods are mostly water and tree parts are mostly cellulose or lignin, all of which are low in nutrients. Grasses and roots are good foods for those species that live in savanna-woodland habitats where grasses are abundant (e.g., baboons), however most primates live in the tropical forests. Vertebrate meat and seeds are also nutrient dense, but require hunting skills or specialized mastication or behavior to make use of them. Of the 131 species surveyed, only some baboons and chimpanzees regularly hunt mammalian prey (Strum 1981; Teleki 1981), and only two

monkey species, Cercopithecus neglectus and Colobus satanas, include seeds as major foods. Chimpanzees, bonobos, and baboons have been seen to use rocks to break open seeds to eat the contents, but this requires much effort and time, which takes away from feeding on more easily acquired foods.

The human primate, not included in Harding’s survey, is unusual in that seeds, grasses, roots, and vertebrate meat are major components of both modern and ancient diets. Seeds, grasses, and roots have their nutrients protected by cellulose membranes that must be mechanically broken. This can be done either by mastication or by using technology. People, and our hominid ancestors dating back to Australopithecus, possess the anatomy (e.g.,small canines, flattened molars, and enlarged pterygoid muscles-the muscles that move the lower jaw from side to side) that allows for a type of chewing called rorary grinding, which can break cellulose. People, and our ancestors of the genus Homo, are also dependent on technology (e.g., tools, fire) for food processing (Figure 6.1). Technology is also required for hunting at a level that makes vertebrate meat a regular part of the diet.

A second reason for selectivity is the coevolution of primates and their foods. Coevolution refers to the interactions of different species of living organisms that exist in the same community, which result in genetic change in those organisms over time. Predator-prey relationships are a common example of coevolution. Animals can move, and animal prey may run, jump, or fly away to evade capture. Over time, there will be selection for predators that are better suited to capture their prey and selection for prey that are better able to avoid capture. In contrast, plants are stationary but not defenseless. Plants produce a host of noxious or toxic substances (called secondary compounds), such as tannins and alkaloids, to discourage their predators. Plants may also evolve edible parts with low nutritional content (Hladik 1981) or seeds and fruits with coverings too hard to pierce (Kinzey and Norconk 1990), thus making those parts less attractive as food items to primates. In a review of the literature on secondary compounds, Glander (1982) found that the rich appearance of the tropical forest may be deceptive, for many primate species avoid a large percentage of potential plant foods. Glander concludes that the selectivity of primates for plant species and parts of plants must be viewed as a strategy balancing “the nutrient and secondary compound content variation in these foods” (p. 1.).

A third reason for selectivity is that primates have a worldwide distribution as an order, but are localized as genera into dozens of populations restricted to species-specific habitats. Thus it is not surprising that many primates, despite their evolutionary heritage of an eclectic food base, have, in practice, species-specific diets. The tamarins and marmosets of South America, for example, eat insects, fruits, and foliage, which are food items common to most primate diets, but also require tree sap for survival. The tree sap is the major source of calcium in their diet (Sussman and Kinzey 1984). These primates have clawlike nails used to cling to tree trunks and procumbent lower incisors used to gouge bark and release sap. No other group of primates has this set of anatomical specializations for tree sap consumption.

HUMAN DIET EVOLUTION

People also have unique requirements and specializations related to nutrition and diet. All primates require a relatively high-quality diet, but people require a higher quality diet than any other species. Leonard and Robertson (1994) compared the diet of 5 human foraging societies (!Kung, Ache, Hiwi, Inuit, and Pygmies) to 72 nonhuman primate species and found that diet quality of the human groups was almost twice that of other primates of the same body size. The human ability to include seeds, roots, and meat in the diet increases quality, as these are nutrient-dense foods. Building on the research of Martin (1983), Leonard and Robertson show that the need for high diet quality is a consequence of the human brain being several times larger than expected for a primate their size. Using estimates of brain and body size for extinct hominids, Leonard and Robertson estimate that humanlike dietary requirements evolved with the appearance of the genus Homo. But the only way to find out what our ancestors actually ate is to look at the evidence, which comes from the study of remains of hominids and their activities.

ARCHAEOLOGY AND FOSSIL STUDIES

Archaeological methods “include the identification of edible materials, functional analyses of artifacts employed in food preparation, coprolite [fossil feces] analysis, information on paleohabitat, and analyses of [hominid] skeletal material” (Sillen and Kavanagh 1982). Paleontological data are derived from the kinds and percentages of fossil remains found at a site. Each type of evidence contributes some knowledge, but each has serious limitations.

The association of hominid fossil remains with the skeletal remains of other fossil vertebrates may result from geologic forces, such as rivers carrying dead carcasses to a central location or a volcanic eruption burying simultaneously a community of animals, rather than hominid food-gathering behavior. Early speculation by Dart (1957) that the bone accumulations at the South African cave sites of Australopithecus represented hominid hunting activity are now considered incorrect. Rather, Brain (1981) argues that the fossil remains, including the hominids, represent the activity of nonhominid carnivores, especially leopards, and geological forces. Dr. Brian aptly names his book on this subject The Hunters or t/e Hunted, and his conclusion is that the early hominids were the prey of the leopards.

Research conducted during the 1980s produced a 180-degree shift in the fossil evidence for the evolution of human hunting. In The Descent of Man, Charles Darwin (1871) proposed that hunting large game provided much of the selection pressure for human evolution. That view persisted through the 196Os, and the book Man the Hzmfer (Lee and DeVore 1968) represented majority opinion that uniquely human characteristics, such as bipedalism, chapter by Washburn and Lancaster in that volume). Implicit in this argument is the notion that the type of diet consumed by human ancestors played a significant role in the evolution of human biology and behavior.

This notion is reasonable, but the explicit assumption of carnivory and hunting became less acceptable as existing evidence was reevaluated and new evidence discovered. The existing data, based on fossil and archaeological remains and the study of living hunting and gathering people such as the !Kung and Australian Aborigines, showed that gathering and processing plant foods was the main activity of tropical foragers. Moreover, women in living foraging societies provided most of the calories consumed by these people. These observations turned “man the hunter” into “woman the gatherer,” and the hunting hypothesis was attacked for both lack of data and its male-biased implications (Zihlman 1981).

The new evidence is based on analyses of bone and stone tool material associated with early hominids. Potts and Shipman (1981) used scanning electron microscope images of mammalian long bones dating to 1.7 million years ago to show that cut marks produced by stone tools were incised above those made by carnivore teeth and the teeth of known scavengers, such as porcupines. Assuming that the order of markings reflects the order of use by hunters and scavengers, the hominids were the last to have at the bones-even after porcupines. Subsequent analysis shows that hominids may have been collecting bones for their marrow and brain tissue rather than for any meat still remaining on the surface of the bone (Binford 1987). Marrow and brain are high in fat and protein, but few carnivores have the morphology necessary to break open large long bones. Hyenas have the ability to exploit marrow and are formidable predators and scavengers but are most active at night (Schaller and Lowther 1969). Hominids are most active during the day and thus could scavenge for carcasses with less threat from hyenas.

The invention of stone tools, first manufactured by hominids about 2.2 million years ago, may have been a dietary adaptation for extracting marrow. At Olduvai Gorge there are sites where the bones of large game animals (from gazelles to elephants) are found together with stone tools. The tools are called scrapers and choppers. Blumenschine and Cavallo (1992) report that the bones are mostly from limbs and skulls and