The Evolution Of Human Nutrition Biology Essay
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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.
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
Glucose Fat or Lipid Linoleic acid Linolenic acid
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
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.
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.
Dietary Frequency and Major Diet Components of 131 Primate Species
Soil plant foods
Hunted and scavenged
Grasses and roots
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 that these are precisely the animal parts that only hyenas and tool-wielding hominids can crack open. Further, they report that one-half hour's work with a chopper can yield enough calories from the marrow and brain of a carcass the size of a wildebeest to meet an adult's daily energy requirements.
Hominids may also have scavenged for larger pieces of meat. Cavallo (1990) studied the ecology and behavior of leopards in Tanzania. Most carnivores, such as lions and hyenas, leave their prey on the ground and consume most of the internal organs and limb meat within a few hours after prey over several days. The kill may even be left unattended for up to ten hours, for other terrestrial carnivores ignore carcasses hanging in trees. Cavallo believes that human ancestors may have scavenged these arboreal caches of meat. This speculation is supported by the South African cave evidence of Brain (1981), which shows that australopithecines and leopards Iived together and that the hominids were often the prey of the carnivores. Cavallo argues chat by the time of the appearance of Homo, some hominids may have reversed the predator-prey relationship. There are modern-day reports of groups of baboons killing leopards as well as confirmed observations of chimpanzees scavenging tree-cached leopard kills and taking and eating leopard cubs (Cavallo 1990), stone tool-wielding hominids may have done the same on occasion.
Perhaps it was the occasional (or regular?) consumption of leopard that caused the hypervitaminosis A of the H. erectus individual from the Koobi Fora formation, located on the eastern shore of Lake Turkana, Kenya. The skeleton is dated to 1.6 million years B.P. (Walker et al. 1982), and analysis indicates that it was female and has "striking pathology" in the long bones of the limbs. These bones have a deposit of abnormal coarse-woven bone, up to 7 mm chick in places, above the normal skeletal tissue on the outer surface of the bone. Walker and his colleagues consider many possible causes for this pathological bone growth and conclude that an overconsumption of vitamin A (hypervitaminosis A) is the most likely cause. Similar cases of hypervitaminosis A have occurred in arctic explorers who consumed the livers of polar bear and seal. The liver stores vitamin A, and the liver of carnivores, who are at the top of the food chain, usually contain the greatest amounts of this vitamin. Walker et al. suggest that the cause of the bone pathology in this specimen of H. erectus was due to eating the liver of carnivorous animals.
Despite the evidence for scavenging animal carcasses and, perhaps, preying on leopards, the bulk of the hominid diet has almost always been from plants. The stone tools of the early hominids may also have been used to process plant foods that were difficult to chew, such as seeds. Walker (1981) and Kay (1985) studied the finer details of early hominid dental structure and tooth wear using the scanning electron microscope and tooth wear experiments. These researchers propose that the diet of the early hominids, including Australopithecus and H. habilis, was largely herbivorous, including softer plant foods (leaves, fruits) as well as the tougher seeds and tubers.
Given all of the evidence now available, perhaps it is safest to say that the gathering of plants, insects, birds' eggs, and other relatively immobile foods along with the scavenging of marrow from carnivore kills typified early hominid food behavior. The early hominid dietary pattern continues through H. erectus times. Binford (1987) reanalyzed fossil material from Torralba, a H. erectus site in Spain, and Zhoukoudian, a cave site near Bejing, China, spanning the period from H. erectus to H. sapiens. During the H. erectus period of occupation (250,000to 450,000 years B.P.), both sites show evidence of the gathering of plant foods and scavenging, rather than hunting. The animal bones at these sites appear to have been processed and consumed on the spot, rather then carried to any sort of "base camp." If this is so, then past theories about the evolution of human biology and behavior-including bipedalism, large brains, division of labor, sharing, and intense parental investment in off- spring, that depended on hunting and "family style dining" at home bases have to be rejected. Binford (1984) states that convincing evidence for the regular hunting of big game does not appear in the fossil record until 90,000 years B.P. at the earliest.
H. erectus added fire to its repertoire of technology. Fire, which may have been used as early as 1.4 million years ago and was certainly controlled by 750,000 years B.P., provided warmth, light, protection, and a new way to process foods. Where and how cooking was invented is a matter for speculation. Cooking, by roasting or boiling, increases the nutritional benefit of many vegetable foods by helping to break down the cellulose in those foods, which is undigestible to people. Fire may be used to open large seeds that resist even stone tools. Cooking, especially drying or smoking, helps to preserve foods for storage. Fire may also be used to obtain foods, especially when used to drive game toward a convenient killing site. All of these uses of fire did not appear simultaneously, and many appear to be the invention of H. sapiens rather than H. erectus. What is certain is that the controlled use of fire was a significant addition to hominid technology with profound consequences for nutritional status.
Coprolite analysis might seem to provide unequivocal evidence of dietary habits, but it too is subject to misinterpretation. First, the coprolite must be identified as unambiguously being from a hominid. Second, coprolites can only verify that a particular substance was eaten. That substance may or may not have been a food item itself, it may have been ingested coincidentally along with a food, such as a seed or insect clinging to an animal or plant. Third, only undigestible substances will be found in feces and those substances must be suitable candidates for fossilization to be preserved in a coprolite. Thus, coprolite analysis may provide a very biased picture of the true dietary intake. Even so, considerable information has been obtained about the diet of prehistoric humans, and limited information about the diet of hominid species ancestral CO modern people, using coprolite analysis. The animal affinity of desiccated coprolites can be determined by placing the specimen in a trisodium phosphate solution for 72 hours. Human coprolites produces this effect (Bryant and Williams-Dean 197.5). Other characteristics of human feces are inclusions of charcoal and the presence of undigested animal parts from a wide variety of species. Charcoal comes from cooking food over a wood fire. Since people cook their food and other animals do not, the presence of charcoal in feces is indirect evidence of a unique human behavior. People also have an eclectic diet compared to most other mammals, so undigested parts from a wide variety of species is another indicator of the human affinities of a coprolite. More than 1,000 paleoindian coprolites from the American southwest have been identified and analyzed. One group of specimens was collected from Texas sites that date from 800 B.C.E. to 500 C.E., representing the temporary camps of hunting and gathering peoples (Bryant 1974). By comparing the pollen content of the coprolites with that of the adjacent soils, it was determined that the people had consumed high quantities of flowers. Because the physical characteristics of flower pollens are unique to each species, it was possible to determine that flowers of agave, sotol, yucca, prickly pear cactus, gilia, and leadtree were popular foods. Also found were remains of wild onion bulbs, bark, grasshoppers, fish, small reptiles, and snails. Although not the current cuisine of Texas, this diet is typically human in its diversity of species. The flower pollen even provides a time frame for the occupation of the sites of spring and early summer. Coprolites from paleoindian sites in New Mexico, Arizona, and Texas contain pollen from plants of known pharmacological value, suggesting that people have a long history of consuming plants as medicines as well as foods (Reinhard 1989). Willow, an analgesic with essentially the same active ingredient as in aspirin, Ephedra, an antihistamine, and creosote, an antidiarrheal, are the most concentrated pollens in the samples. Ethnographic evidence shows that these three species were, and are still, widely used as medicines by Native Americans (Moerman, 1986, 1989). Willow tea is used for the treatment of many aches and pains, Ephedra tea is prescribed for the stuffy noses of the common cold, and creosote is indicated for any type of loose bowls. Reinhard (1989) states that the analysis of these coprolites "demonstrates the antiquity of folk remedies and provides circumstantial evidence of certain disorders suffered by prehistoric peoples" (p. 2).
The oldest verified coprolites of a hominid species are from the H. erectus site of Terra Amata located on the French Mediterranean. These coprolites may be as old as 300,000 B.P, and they are heavily mineralized. They have only a slight reaction to trisodium phosphate rehydration (Bryant and Williams-Dean 1975). The specimens contain sand grains, charcoal, and mollusk shell fragments. The sand and shell are expected, since Terra Amata is a beachfront site, and the charcoal helps establish that foods were cooked before consumption (maybe evidence for a prehistoric clam bake!). modern (e.g., modern people have more gracile skeletal features than archaic forms). Care was taken to control for differences in the amount of calcium and strontium in the soils of different fossil sites and other confounding geological variables. It was found that Sr/Ca ratios in bone increased with time, suggesting more plant food in the diet, but the increase occurred 20.000 vears after the modern human form appears in the fossil record. Schoeninger concludes that the morphological transition from archaic to modern H. sapiens was not due to the utilization of new foods, rather it was due to "alterations in the means of procuring or processing the same kinds of foods that had been utilized earlier in time" (p. 37). In other words, behavioral and cultural changes were more important than diet change per se in bringing about the biological form of modern humans. This along with the other examples of trace element and stable isotope analysis clearly shows the biocultural nature of people and food.
STUDIES OF LIVING HUNTERS AND GATHERERS
Today, 99.9 percent of people derive their food from some form of agriculture. However, from the time of the Australopithecus until about 10,000 years ago, a time period that covers 99 percent of human evolution, all hominids lived by foraging-the gathering, scavenging, and, more recently, hunting of wild foods. Most human physical traits, and perhaps many behavioral propensities, evolved during the time that hominids lived as hunters and gatherers. That biobehavioral evolution includes current human dietary requirements, adaptations for food acquisition and processing, and biocultural responses to food intake. Studies of the few remaining cultures of hunting and gathering peoples offer an indirect view of that style of life, now nearly extinct. These ethnographic and ecological studies complement the information derived from paleontological and archaeological sources.
Foragers are a diverse group geographically and culturally, ranging from the arctic Inuit and Eskimo, to the tropical forest Ache (Paraguay), to the dry scrub San (Africa) and the desert Australian Aborigines. Yet research shows some consistencies in behavior and diet. The diversity of food resources utilized is high among gathering and hunting peoples compared with agriculturalists. The !Kung San of southern Africa, for instance, eat 105 species of plants and 144 species of animals (Lee 1984). The Australian North Queensland Aborigines exploit 240 species of plants and 120 species of animals (Gould 1981). The Ache forage on fewer species, about 90 types of plants and animals (Hill and Hurtado 1989). Even the Dogrib, residing in the subarctic of Canada, gather 10 species of plants and 33 species of animals (Hayden 1981). That is a small food base for hunters and gathers, but still a large number relative to agriculturalists who, on a worldwide basis, subsist largely on four species of plants and two species of animals. Of nine species of staple plant foods, wheat, rice, potatoes, and maize together account for 1,680 of the 2,284 million metric tons consumed (sorghum, sweet potatoes, barley, millet, and cassava are the other five staples, [Garine 19941). Of the animal foods, cattle and hogs account for 80 out of every 100 metric tons of domesticated animal meat. Poultry, lamb, goat, buffalo, and horse make up the bulk of the remaining 20 metric tons (Bogin 1985).
A second common feature is that gathered foods (plants, insects, birds' eggs, turtles, etc.) are the primary subsistence base in most foraging societies. Lee (1968) compared 58 forager groups and found that the primary subsistence source was gathering for 29, fishing for 18, and hunting for 11. Ten of the hunting groups and 16 of the fishing groups lived north or south of the 40-degree parallel. Thus, not only is gathering the most common subsistence pattern, it is correlated with tropical, subtropical, and low-temperate habitats. Such habitats were the home for all species of hominids until the middle to late Paleolithic period.
Often the use of many species for subsistence is correlated with the high diversity, low density, or seasonality of food items in the environment. In habitats where low density is combined with the wide dispersal of foods, foragers must be mobile and live in small groups. Thus a small, mobile social group is a third typical feature of forager societies, but, as shown in Table 6.3, it is not a universal feature. Leaving aside the Nootka, average group size ranges from 9 to 55 and average densities range from 1 to 200 people per 100 square miles. Mobility ranges from daily movement from camp to camp in the case of the Ache to seasonal sedentariness at one camp (e.g., a winter lodge) in the case of the Mistassini (hunters of the Canadian borealforests).
The Ache are unusual in their daily movement, but contemporary Ache
Table 6.3 Hunters and Gatherers
Population density/per 100 mi2
Freq. Of moves
As needed=45 days?
!Kung San (Africa)
Giwi San (Africa)
Ache (S. America)
Guayaki (S. America)
Western Desert Australia
Source: Hayden 1981. Ache data from Hill and Hurtada, 1989.
SUMMARY OF EVIDENCE FOR THE EVOLUTION OF HUMAN NUTRITION
Table 6.4 lists the nine universal features of human nutrition and food behavior. Also listed in the table are the sources of evidence that allow an understanding of the origin and function of these universals. The human place in nature as primates explains our broad requirements of essential nutrients. Fossil and archaeological evidence accounts for the development of cuisines and the technology for food acquisition, preparation, and storage.
The study of living hunting and gathering peoples complements and supports these other sources of evidence. Five features of food and behavior are typically found in hunting and gathering societies: (1) a high diversity of food types; (2) greater dependence on gathering over hunting; (3) small, mobile social groups; (4) dependence on technology for acquiring and processing foods; (5) and division of labor and sharing. Additionally, forager studies detail the nature of human food transport for exchange and sharing and provide some information on the origin of food taboos and nonnutritional uses of foods.
The Nine Universal Features of Human Nutrition and Food Behavior and
the Sources of Evidence Used to Study Their Evolution
Sources of evidence
1. Large number of essential nutrients
Primate studies, biomedical research
2. Each culture has a cuisine
3. Extreme omnivory
Primate studies, hunters& gatherers
4. Transport of foods
5. Storage of foods
6. Complex technology for acquisition & preparation
7. Sharing and division of labor
Primate studies, hunters& gatherers
8. Food taboos
9. Non-nutritional use of potential foods
Using the methods of research described here, archaeological and paleontological evidence, ethnographic studies of living hunting and gathering people, and the nutritional analysis of wild plant and animal food, Eaton and Konner (1985) reconstructed the diet of Paleolithic people living during the last glacial period in western Europe, about 15,000 years ago. Garn and Leonard (1989) point out that this diet was not typical of the majority of people alive at that time. The majority lived at tropical or subtropical latitudes and consumed more wild grains and less animal meat-recall Schoeninger's (1982) analysis of Paleolithic diets from Israel. Garn and Leonard state that "many of our ancestors ate poorly,. . . and they were often at risk for vitamin deficiencies, food-borne diseases, and neurotoxins" (1989: 337).
Despite these caveats, the Paleolithic diet reconstructed by Eaton and Konner offers some useful data, especially when compared with the modern American diet.
Table 6.5 compares this Paleolithic diet with that of modern Americans and U.S. government recommendations for a safe and healthy diet. These glacial people ate more protein and less fat than we do. Eaton and Konner's analysis of living foragers indicates that the average diet consists of 3.5 percent of calories from meat and 65 percent of calories from vegetable foods. Although plants contribute protein to the diet, Eaton and Konner estimate that most of the protein was from animals, including fish, insects, and other invertebrates. Fat intake was lower in the Paleolithic due to the low content of fat in wild game. The average carcass fat content of 15 species of wild herbivore surveyed by Eaton and Konner is 3.9 percent compared to an average of 25 to 30 percent in domesticated carcasses (cattle, hogs, etc.).
Moreover, compared with domesticated meat, the fat of wild game is about five times higher in the polyunsaturated form. Along with plant foods rich in polyunsaturated fats, the paleolithic diet has a high ratio in polyunsaturated to saturated fats. Cholesterol intakes appear to have been higher in the ancient diet. In the early 1980s. however, the ancient and modern diets contained similar amounts of cholesterol, and fat intake of the American diet was about 42 percent of total calories. It seems that Americans have learned to eat foods with less fat and cholesterol. Unfortunately, Americans are also eating more total food (i.e., calories) than in 1980. So, despite a decrease in fat consumption there has been an increase in body weight, mostly due to fatness, for both average and obese children and adults (Yip and Scanlon 1995).
The Paleolithic Diet of 15,000 Years B.P., the Current American Diet, and
One Set of Dietary Recommendations for the United States
Daily Intake Paleolithic American' Recommended2
Daily intakes M W
Total dietary energy (%)
Ascorbic acid [mg]
Simple sugars [g]
`.Amcrican diet for adults E-29 years old surveyed between 1988 and 1991, published by the Centers for Disease Control, 1994: hl = men, W = women. Based on a diet of 3,025 calories per day for men and 1,957 calories per day for women. `Recommendations of I1.S. Senate Select Committee and Food and Nutrition Board, National Academy of Sciences. Values for adults, sexes combined. `Ratio of polyunsaturated to saturated fats from ail foods. Source: Paleolithic diet: Eaton and Konner 1985: American diet: Guthrie and Picciano 1995,appendix K.
The modern ethnographic data and the archaeological data indicate that Paleolithic people would have gathered a wide assortment of wild plant foods and many species of animals, ensuring variety in both vitamin and mineral content and in taste and appearance. In contrast, the many people living in agricultural and industrial societies eat from an extremely narrow range of food options. Modern people eat more wheat, rice, potatoes, and maize than the next 26 most often consumed plants combined (when did you last eat a turnip?). There are many reasons for this. For most of the world the reasons are associated with economics. Wheat, rice, potatoes, and maize are grown on a large scale to make profits for national or multinational agribusiness corporations. The intensive production of these and a few other crops is very efficient in terms of business practices and profits. These crops may be produced relatively cheaply, making them more affordable to the 80 percent of the world population who live in less-developed nations and who are at or near the poverty level. The more affluent 20 percent of the world's people, living mostly in the more-developed nations of Europe, Japan, Australia, and North America, can eat a much wider variety of foods. They can afford to buy more expensive foods that are produced in limited quantities and often shipped long distances. The Japanese and French, for example, eat dozens of species of animals, including many mammals (rabbits, sheep, horses) and ocean species (shell fish, sea urchins, fish) as part of their regular diet. The modern American diet, on the other hand, is much more restricted in food choice. A survey of most supermarkets will reveal a limited variety of animal protein sources (when did you last eat horse, rabbit, or even fish?). Americans eat more ground beef, usually in the form of hamburgers, than any other animal protein food. It is estimated that 12,000 hamburgers are consumed each minute in the United States-a rate of 200 per second (Lieberman 1991). The consumption of ground beef also accounts for about one-half of the total fat and three-fourths of the saturated fat in the American diet. Surveys of food consumption generally find that the uniformity and limited variety of offerings available at fast-food restaurants depicts the current American diet very well.
The Eaton and Konner reconstruction also indicates that our ancestors ate much more fiber, calcium, and vitamin C, but far less sodium. Our ancestors ate simple sugars only in natural forms, for instance from fruits, but today we each eat about 124 pounds of simple sugar (mostly sucrose and corn syrup) a year. Paleolithic foragers consumed no dairy products, except for mother's milk during infancy, and little alcohol. Consumption of dairy foods is a by-product of animal domestication, and thus less than 12,000 years old.
Even today, dairy products are staple foods in only a few societies. Most adults lack the enzyme lactase needed to digest the milk sugar lactose (Kretchmer 1972). Some societies do eat cheeses or yogurt, for these foods have their lactase digested by bacteria, but these foods are often too expensive for most of the world's people. The wealth of the developed nations allows [their populations to consume large quantities of dairy products. Inthe [United States, 20 percent of protein, and most calcium, comes from milk and cheeses. These foods, unfortunately, also contain high amounts of fat and sodium, which also typify the American diet. Alcohol is, basically, also a product of domestication-the domestication of grains such as maize and barley. Some alcoholic beverages (beer, mead, wine) contains some nutrients, but alcohol itself provides no essential nutrients. Even so, alcohol contains energy-seven calories per gram-and contributes a measurable percent of calories to the American diet.
High intakes of fat, especially saturated fat, simple sugars, sodium, and alcohol are linked with health problems, such as obesity, heart disease, and liver disease. Apparently, Americans are aware of a problem, for example, millions of dollars are spent annually for weight loss programs. The weight loss programs usually have little long-term success, indeed the average weight and fatness of Americans has increased in the last few decades. A narrow diet is also a risk for nutrient deficiencies, such as the low calcium intake of many Americans. The response of the people is to purchase nutritional supplements and special "health foods." The U.S. Food and Drug Administration (note that food and drugs are lumped together by American culture) estimates that 40 percent of adults regularly take at least one vitamin and mineral product (Moss et al. 1989). Taking vitamin pills to compensate for a narrow diet was not the nutritional behavior followed by our ancestors. Consumption of vitamins via pills is not bad, or harmful, in and of itself. Our bodies make no distinction between the vitamins in food and those synthesized by chemists.
Eating food, however, provides the physical and emotional satisfaction of taste, aroma, and a full stomach, along with other nutritional factors that are linked with good health, such as fiber. Of course, one can also buy and consume "fiber pills." Indeed, there are pills to reduce high serum cholesterol levels, induced by all those hamburgers, and to lower blood pressure, induced, in part, from our sodium overload. Perhaps it is best to view American nutritional habits as part of a biocultural system with its own internal logic. The system works, in the sense that there are fewer nutritional deficiency diseases in the United States today than ever before.
Nutritional oversufficiency is the single biggest dietary problem in the United States. In this regard, it is important to mention one other major difference between Paleolithic people and contemporary Americans. The former were required to perform high levels of both aerobic and anaerobic exercise, while the latter are sedentary ("couch potatoes" in the vernacular).
Foraging people of the past and of today have the physique and cardiovascular conditioning of athletes. No amount of diet change or pill consumption for Americans and people of the other developed nations will improve health without a simultaneous increase in physical activity.
AGRICULTURE AND THE DECLINE OF HUMAN NUTRITION AND HEALTH
Some of the nutritional problems of modern world societies are: (1) a narrow food base, leading to deficiencies for some essential nutrients, (2) an inadequate supply of energy (i.e., under nutrition of total calories from all food sources) for about 60 percent of the world's population, especially the poor in the least-developed countries, and (3) an oversupply of energy, leading to obesity and related diseases in the developed nations and, increasingly, among the more affluent in the developing nations. The immediate causes of these problems include a host of social problems, such as poverty and other economic inequalities, political unrest (such as civil and ethnic wars), inadequate water management, and unregulated population growth.
Although these are significant proximate causes for the world's current nutritional crisis, there is a more fundamental explanation that had its origin at the end of the Paleolithic period. The major culprit of the nutritional dilemma is agriculture. More recently, industrialization and urbanization have compounded the effects of agriculture on the nutritional status and health of human populations. Agriculture, industrialization, and urbanization are often stated to be the hallmarks of "progress" of the human species. Although progressive in a technological sense, each of these achievements has had negative consequences for human nutrition and health.
There is much evidence from the developing nations of the world that the food production systems of rural people correlate strongly to their nutritional status. The classic study of Indonesian peoples by Geertz (1963) shows that simple horticulturalists have the most abundant variety and amount of foods, while food shortages and frank malnutrition are most common in areas of intensive rice agriculture. Whyte (1974) extended these findings to much of tropical Asia. Whyte's analysis shows that foragers, horticulturalists, and fishing societies have diversified diets, but often inadequate calorie intakes. These societies are better nourished, however, than peoples practicing mixed agriculture-pastoralism and intensive irrigation agriculture, especially of rice. The agriculturalists suffer marginal to serious malnutrition for total calories and many vitamins, minerals, and protein.
The dilemma of modern agricultural societies has deep historical roots. Studies of archaeological populations show that several indicators of biological stress increase with the transition from foraging to horticulture and agriculture (Cohen and Armelagos 1984). These stress indicators include bone lesions due to anemia (called porotic hyperostosis), deficits in enamel formation in teeth (hypoplasias), loss of bone tissue from the skeleton, bone lesions due to infectious disease, such as tuberculosis (called periosteal repetjon), and reduced skeletal growth in children and adults (Goodman et al. 1988). The Dickson Mounds site of the Illinois River Valley provides a classic example. From C.E. 950 to 1300 the human population of that area hanged from mobile foragers to sedentary intensive agriculturalists. During "this short time period, "the shift in subsistence led to a fourfold increase in iron deficiency anemia (porotic hyperostosis) and a threefold increase in infectious disease (periosteal reaction). The frequency of individuals with both iron deficiency and infectious lesions increased from 6% to 40%" (Goodman et al. 1988~180).
The incidence of enamel hypoplasias (malformations of the tooth crown that include pitting, linear furrowing, or complete lack of enamel) also increases from the forager to agricultural period. These dental deficiencies occur when malnutrition or disease disrupt the secretion of enamel-forming material. For the permanent teeth that process takes place during infancy and childhood. Thus enamel hypoplasias leave a permanent record in the teeth of nutritional or disease stress that people experienced in early life. In the Dickson Mound skeletal material the prevalence of hypop
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