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Levetin−McMahon: Plants and Society, Fifth Edition

III. Plants As a Source of Food

11. Origins of Agriculture © The McGraw−Hill Companies, 2008

177

11 ORIGINS OF

AGRICULTURE

CHAPTER OUTLINE Foraging Societies and Their Diets 178

Early Foragers 178 Modern Foragers 179

A CLOSER LOOK 11.1 ForensicBotany 180

Agriculture: Revolution or Evolution? 181 Early Sites of Agriculture 181

The Near East 181 The Far East 182 The New World 183

Characteristics of Domesticated Plants 184

Centers of Plant Domestication 184 Chapter Summary 185 Review Questions 186 Further Reading 186

KEY CONCEPTS 1. Early human societies were based on a

foraging lifestyle in which wild plants were gathered and animals were hunted.

2. Agriculture evolved independently in several areas of the world, most likely as a natural consequence of intensified foraging.

3. The earliest evidence of agriculture dates back at least 10,000 years in the Near East, Far East, and Mesoamerica.

4. Domesticated plants are genetically different from their wild counterparts, and many can no longer survive without human intervention.

C H A P T E R

Starch grains, which exhibit a characteristic cross in polarized light, can be used to identify species and distinguish wild from cultivated forms. Starch grains of arrowroot (Maranta arundinacea) have been found in Ecuador that are 6000 years old.




178 U N I T I I I Plants as a Source of Food

The human species, known as Homo sapiens, hasexisted for about 250,000 years. For most of that time, humans survived as foragers or hunter-gatherers,

gathering wild plants and hunting animals in their natural environment ( fig 11.1 ). Around 10,000 years ago in many areas of the world, there was a shift in human endeavor from foraging to farming. Most authorities agree that agriculture arose independently in different areas over several thousand years. Why this shift occurred can only be theorized, but the development of agriculture formed the basis of advanced civilization in both the Old and the New Worlds. Over the centuries, agricultural societies spread into those environ-ments that could be easily adapted to agriculture, and forag-ers gradually became restricted to marginal areas. By the late twentieth century, foraging societies had largely disappeared, constituting only a tiny percentage of the human population and limited to a few tropical rain forests, deserts, savannas, tundras, and boreal forests.

FORAGING SOCIETIES AND THEIR DIETS Foraging societies are by no means all alike in the types of food they eat. Some groups, such as the Arctic Inuit, subsist almost entirely on meat; at the other extreme, the Hadza of

Tanzania are largely vegetarian, rarely hunting for meat. Other groups such as the !Kung (the exclamation point is pronounced as a click) of southern Africa, however, have had a more varied diet, largely plant based but supplemented by eggs, insects, fish, small animals, and meat from the hunt.

Many hunter-gatherers have utilized plants by gathering seeds, flowers, roots, and tubers and have a fairly thorough knowledge of the botany in the area. From experience, they know which plants are edible, which are poisonous, which have medicinal properties, which are sources of dyes, which could be used for weaving or building materials, and even which have psychoactive properties. By looking for certain visible clues such as flowering on so-called calendar plants, foragers know if tubers are ready to be dug up or if turtles are laying their eggs. They have developed remarkable methods to prepare edible foods, even from plants with toxins, such as cassava, which contains poisonous hydrocyanic acid.

Early Foragers Archeological investigations have supplied knowledge about the diet of early humans from many sources, and radiocar-bon dating of artifacts can provide an estimated time frame. Fossilized remains of both plants and animals have been found in early settlements ( fig. 11.2 ). Plants in the diet have been identified from charred seeds and preserved fruits or

(a) (b)

Figure 11.1 Native North Americans of the Pacific Northwest foraging in the early twentieth century. (a) A Hupa man hunts salmon with a spear. (b) A Pomo woman uses a beater to gather seeds into a basket.




C H A P T E R 1 1 Origins of Agriculture 179

other plant parts while bones, teeth, feathers, scales, fur, and shells indicate the animals in the diet. Microscopic remains include plant fibers, plant crystals, and pollen, with crystals and pollen especially useful in identification. Coprolites,fossilized fecal materials, provide direct evidence of the diet because some plant materials, especially seeds and pollen, can pass through the digestive tract largely intact. Often middens, or dump sites, from a human encampment provide a concentrated source of plant and animal remains. (See A Closer Look 11.1—Forensic Botany.)

Grinding stones, sickles, and digging implements pro-vide information on the food in the diet but do not indicate if the plants harvested were wild or domesticated. Tools of the hunt also provide some information on the size of the animals hunted and the method of the kill. Depictions in cave paintings (of animals as well as hunting and gathering activities), pottery fragments, and clay figurines are other windows to the past.

In some excavations at Wadi Kubbaniya in the Nile Valley of Upper Egypt, archeologists have dated plant remains of a hunter-gatherer settlement from 17,000 to 18,000 years ago. The charred remains of fruits, seeds, and tubers from 25 plant species have been found; interestingly, contemporary forag-ing societies have utilized these same plants or closely related species. The most abundant plant remains found were the

tubers of wild nut grass, a type of sedge. Analysis of modern samples of these tubers indicates that they are high in carbo-hydrates and fiber but low in protein; however, the protein is of good quality because it is high in lysine, one of the essen-tial amino acids. Mature nut grass tubers also contain toxins, but these could be easily removed by various methods still in use today. It is believed that this tuber served as one of the dietary staples, along with acacia seeds, cattail rhizomes, and palm fruits. Evidence from this and other Paleolithic (OldStone Age or preagricultural societies) sites indicates that early foraging groups had a remarkably varied plant diet.

Modern Foragers Much of the knowledge about the foraging way of life has been documented by studying modern foraging societies such as the !Kung San of the Kalahari Desert of southern Africa. These people live in the tropical savannas that border the Kalahari in what is now southeastern Angola, northeastern Namibia, and northwestern Botswana. The !Kung have for-aged in this area for at least 10,000 years, continuing the hunter-gatherer way of life until recent times ( fig. 11.3 ). Extensive studies of the !Kung during the 1960s revealed that they utilized over 100 species of plants and 50 animal species; two-thirds of their diet was plant based. The plants

(a) (b)

Figure 11.2 (a) A clay impression fossil of wheat as compared with (b) a present-day species of wild wheat.

Figure 11.3 A rock painting of the !Kung San of the Kalahari Desert of southern Africa depicts hunters and prey.




180

Archeologists have made extensive use of plant remains in reconstructing the lifestyles of ancient foraging and early agricultural peoples. The recovering and processing of plant remains begin the painstaking task of botanical detection. Not all parts of a plant are equally well preserved: seeds, wood, pollen, phytoliths, starch grains, and fibers are among the most informative recoverable remains. The lignified walls of wood and fibers are more resistant to decay than purely herbaceous tissue because lignin can be degraded only by a few types of fungi. Likewise, the lignin, in the sclerified cells of the seed coat, or testa, makes seeds among the most common dietary material recovered from archeological sites. Buried pollen grains are virtually indestructible, owing to the chemical properties of the exine (outer pollen wall). Phytoliths (literally “plant stones”) are crystals formed and found in many plants (box fig. 11.1). They often are created within epidermal cells or between plant cells. The crystals may be composed of calcium oxalate or, rarely, calcium carbonate. Another common component of phytoliths is opaline silica (silicon dioxide). After a plant decays, the phy-toliths are released into the soil and can remain intact for thousands of years. Phytoliths are so distinctive in shape and size that they can be used to identify the presence of a par-ticular plant family, genus, or even species. In fact, phytoliths can be used to separate wild species from domesticated ones and have proven especially useful in dating the origin of agriculture in many sites.

These same principles of plant detection are applicable to forensic science, in which the identification of plants can be used as incriminating evidence. The first criminal case that used botanical information was the famous 1935 trial of Bruno Hauptmann, who was accused and convicted of kid-napping and murdering the young son of Charles and Anne Morrow Lindbergh. The botanical evidence centered on a homemade wooden ladder used during the kidnapping and left at the scene of the crime. After extensive investigation, plant anatomist Arthur Koehler showed that parts of the ladder were made from wooden planks from Hauptmann’s attic floor.

In forensics, even herbaceous plant parts can be useful for identification. In one case, botanical evidence disputed the testimony of an accused rapist. Fragments of tree leaves and bark in his pants cuff indicated that the accused had climbed a tree to get into a window of the victim’s home, rather than being admitted through the front door as he claimed. In cases of suspected plant poisonings, identifica-tion can be made from leaves or fruits of intact plants or even from analysis of stomach contents. In this type of

situation, proper medical treatment depends on accurate identification of the plant or mushroom. Trained botanists and mycologists (scientists who study fungi) are routinely called to hospital emergency rooms for this purpose. Botanical analyses of stomach contents have also played roles in other types of cases: a hunting guide killed a grizzly bear he claimed was eating his supply of alfalfa hay. Botanical evidence showed no alfalfa in the bear’s stomach, only native vegetation. The guide was fined and imprisoned for killing a threatened species.

Forensic Botany

A CLOSER LOOK 11.1

(a)

Figure 11.1a Calcium oxalate crystal in the vacuole of a leaf cell, �270.

(b)

Figure 11.1b Needle-like crystals are recognizable in pineapple pulp.





included a mixture of fruits, nuts, berries, melons, roots, and greenery; one particular nut, the mongongo nut, was a very important high-protein component of their diet. The !Kung diet was very nutritious; they consumed an average of 2,355 kilocalories per person per day, with 96 grams of protein and adequate vitamins and minerals. This diet more than meets the nutritional requirements established for people of the !Kung stature and physical activity. As in most foraging societies, the division of labor was along gender lines, with women doing most of the gathering and men the hunting. Surprisingly, the amount of time spent on foraging activities averaged only about 2.5 days per week, which left plenty of time for leisure and socializing.

Concept QuizHumans survived as foragers of wild plants and animals for hundreds of thousands of years. Agri culture arose relatively recently, roughly 10,000 years ago, in the course of human history.

Explain the success of foraging as a survival strategy for early humans.

AGRICULTURE: REVOLUTION OR EVOLUTION? Archeological evidence indicates that about 10,000 years ago human cultures began the practice of agriculture in several areas of the world. Over the next few thousand years in the Near East, the Far East, and Mesoamerica, agriculture flour-ished. The question that has puzzled archeologists and other scientists is, “Why, after thousands of years of foraging, did hunter-gatherers switch to agriculture?”

Many theories have been proposed to answer this ques-tion. Some state that agriculture was the discovery of a bril-liant sage who, with a flash of insight, realized that if you sow seeds, the crop will grow. There were many variations of this theme. Some held that the brilliant sage realized that plants growing at middens, or dump sites, were growing from dis-carded seeds. Others held that the sage observed seeds buried with the dead (as food for the afterlife) gave rise to plants at grave sites. These theories viewed agriculture as a revolution; in fact, the term Agricultural Revolution was used to describe the transition from foraging to agriculture. It was suggested that this revolution spread quickly because agriculture was thought to be an improvement over the hunter-gatherer life-style in that a dependable food source could be easily grown rather than collected from the wild.

Beginning in 1960, archeologists questioned that view, suggesting instead that the origin of agriculture was not a revolution but the result of a gradual cultural evolution.

They reasoned that hunter-gatherers knew the wild plants, knew how they grew, and would incorporate farming along with foraging as part of an overall food-collection strategy when necessary. For example, certain aboriginal groups in coastal Peru abandoned their farming practices whenever fish became plentiful.

Many archeologists believe that there was a transitional stage between simple foraging, in which small nomadic bands followed the wild plants and animals, and agricultural societies with their sedentary lifestyle. During this transi-tional stage, foraging groups formed settlements but sent out members to hunt and gather. This more complex strategy resulted in changes in the social organization of the groups and permitted populations to increase. This transitional stage lasted for several thousand years in some locations until resource stress or environmental change led to the switch to agriculture. Archeologists believe that in the Near East, for example, the climatic dry period around 11,000 years ago brought about a change in the distribution of cereal grains (wheat and barley). Applying their botanical knowledge, these foragers gradually changed from collecting these wild cereals to cultivating them.

EARLY SITES OF AGRICULTURE Archeological excavations have documented many sites of early agriculture in both the Old and New Worlds ( fig. 11.4 ). The evidence indicates that the earliest sites were in the Far East, dating back approximately 11,500 years.

The Near East Some of the oldest sites of agriculture are in southwestern Asia, in the foothills around the area known as the Fertile Crescent, which today includes parts of Iran, Iraq, Turkey, Syria, Lebanon, and Israel ( fig. 11.4 ). From sites such as Jarmo, Jericho, Ali Kosh, Cayonu, and others, remains of both plants and animals date back 9,000 to 14,000 years. Early plant domesticates include einkorn wheat, emmer wheat, barley, pea, lentil, and vetch while dogs, goats, and sheep were among the domesticated animals. Research sug-gests that the animals were domesticated several thousand years before the plants. Evidence indicates that barley may have been the first crop domesticated in the Near East, approximately 10,000 years ago.

One of the sites that had been particularly well studied was Jarmo in northeastern Iraq, in the foothills of the Zagros Mountains. This area was inhabited approximately 9,000 years ago; it was a permanent farming village with about 24 mud-walled houses and a population of about 150 people. The charred grains of wheat and barley found there were a domesticated type already changed from the wild type; for this genetic change to have taken place, initial cultivation must have predated the age of the remains. In addition to the domesticated plants and animals, the inhabitants of Jarmo





also continued foraging, as evidenced by the bones of wild animals, snail shells, acorns, and pistachio nuts. Artifacts uncovered at the site include flint sickles and grinding stones for harvesting and milling cereal grains as well as clay figu-rines, woven baskets, and rugs.

The domestication of cats apparently took place earlier than previously thought. Most authorities placed the domesti-cation of cats in Egypt around 4,000 years ago. A cat skeleton discovered on the island of Cyprus indicates that people there domesticated the cat around 9,500 years ago. The 8-month-old cat ( Felix silvestris) was buried in a small grave next to a large grave containing a human skeleton. The joint burial suggests a special association between human and cat. Cats were most likely valued in agricultural societies to protect grain stores from mice.

Some researchers question several of the archaeological findings at some ancient sites of early agriculture. Nicole Miller, an expert in archaeobotany at the University of Pennsylvania Museum of Archeology and Anthropology, studies sites in the Near East for evidence of plants used by people during ancient times. She documented a 5,000-year-old site in southwestern Iran that showed an increas-ing presence of charred wild seeds. In previous analyses, the presence of wild seeds at the sites of ancient cook fires was interpreted as spilled food and hence indicated that the plants were consumed by ancient people. Miller has another view. She explains that as the surrounding forests were cleared for fuel and pastureland, the inhabitants turned to the dung of animals as cooking fuel, and thus, the presence of charred wild seeds reveals more about the human impact on the environment than their diet. Similarly, she disagreed with the conclusion that the diversity of wild seeds pointed

to a varied diet for the inhabitants of an 11,000-year-old site in Syria. She deduced that the cooking fuel used was the dung of gazelles, and the wild seeds found were a food source for an animal that was plentiful at this location in the past.

The Far East Excavations of dozens of sites in Asia indicate that agricul-ture arose at several locations in the Far East. These sites include the Yellow River and Yangtze River valleys in China ( fig. 11.4 ). Among the earliest plants domesticated in the Far East were rice, foxtail millet, broomcorn millet, rape, and hemp, with evidence of domesticated cattle, pigs, dogs, and poultry as well.

Current archeological studies in China indicate that rice cultivation began approximately 11,500 years ago along the middle reaches of the Yangtze River. From there, agriculture spread both upstream and downstream. Among the artifacts examined were samples of rice grains, husks, plant remains, and impressions of rice grains in pottery. If these dates are confirmed, this would mean that the domestication of rice predates the domestication of crops in the Near East by about 1,500 years. In settlements to the north, along the Yellow River, foxtail millet was domesti-cated approximately 8,000 years ago and became a dietary staple; it remained the dominant crop in North China until the historical period. Broomcorn millet was also cultivated but not as extensively. Tilling tools, harvesting tools, and grain-processing tools made of stone, bone, shell, or wood have also been recovered from these sites along with bones of domesticated animals.

Yangtze and YellowRiver Basins

New GuineaHighlands

FertileCresent

South AmericanHighlands

Mesoamerica

Eastern NorthAmerica

Figure 11.4 Evidence of the beginnings of agriculture have been found in eastern North America, the Tehuacan and Oaxaca valleys in Mexico (Mesoamerica), the South American highlands, the Fertile Crescent of the Near East, the Yangtze and Yellow River valleys of China (Far East), and the New Guinea Highlands.





Newly discovered evidence strongly indicates that agriculture may have begun independently in the Papua New Guinea Highlands nearly 7,000 years ago. The Kuk Swamp site in the Waghi Valley of central New Guinea shows several indications of early agriculture. Analysis of soil sediments for pollen and phytolith microfossils (see A Closer Look 11.1— Forensic Botany) indicates that the area was subjected to accelerated forest clearing. Deforestation led to the establishment of a grass-sedge swampland. Archeological remains of stakeholes and postholes were also found and indicate planting, digging, and support-ing posts, all practices clearly associated with cultivation. Vestiges of soil mounding and deep channels have been interpreted as practices to improve drainage in the grassy wetland. Evidence of taro and banana, historically two of the most important tropical food crops, have also been found at Kuk Swamp. The percentage of banana phytoliths is higher than would be expected in the area and probably indicates their cultivation. The researchers conclude that this species of banana, previously thought to have been domesticated in Southeast Asia, may have instead been domesticated first in New Guinea and later dispersed to Southeast Asia. Microfossils of taro, including starch grains and needle-like calcium oxalate crystals (See A Closer Look 11.1—Forensic Botany), were recovered from stone tools. Finding a lowland crop like taro in the highlands confirms that this crop was deliberately introduced into this site. All evidence points to New Guinea as one of the primary centers of agri-culture.

The New World In contrast to the Old World, the Neolithic (New Stone Age, or agricultural society) cultures of the New World had domes-ticated an impressive array of plants but comparatively few animals. Among the earliest crops domesticated in the New World were squash, corn, chili peppers, amaranth, avocado, gourds, beans, and both white and sweet potatoes, with only dogs, turkeys, llamas, alpacas, guinea pigs, and Muscovy ducks as domesticated animals. Most of the initial archeologi-cal evidence for early agriculture in the New World has been obtained from the highlands of Mexico and Peru.

Probably the most thoroughly documented site is a group of caves in the Tehuacan Valley of central Mexico. Research in this area was initiated to obtain information on the ancestry of corn. Working with ancient corncobs, archeologists determined that corn had been domesticated in this region by 5,500 years ago ( fig. 11.5 ). Originally it was thought that these corncobs were much older (7,000 years old), but newer dating techniques advanced the time frame. The Tehuacan Valley is one of the few sites where the transition from foraging to farming can be thoroughly docu-mented. For thousands of years, people inhabited the caves seasonally as they foraged for plants and hunted animals. At first, there was a shift from hunting to a more intensified for-aging of plants, along with the domestication of squash and

avocado. Later, the list of domesticated plants expanded to include corn, bottle gourd, two species of squash, amaranth, three species of bean, and chili peppers; however, people still relied on foraging for the majority of their diet. Over the next few thousand years, agriculture became even more important as additional plants (tomato, peanut, guava), the dog, and later the turkey were domesticated. Artifacts such as stone tools, textiles, and pottery were also found. From this evidence, archeologists have been able to reconstruct a picture of the lifestyles of the inhabitants of these caves over a 12,000-year period. At yet another cave in southern Mexico, Guilá Naquitz in Oaxaca, seeds and the fruit rind of a domesticated squash have been dated between 10,000 to 8,000 years ago. This date of domestication is much earlier than what has been obtained for maize, beans, or any other New World domesticate. These findings indicate that farm-ing appeared in the Americas at more or less the same time that it did in the Fertile Crescent and Asia.

Dolores Piperno of the Smithsonian Tropical Research Institute has been a leading investigator into the origins of agriculture in lowland tropical soils of Central and South America. Using phytolith data (See A Closer Look 11.1—Forensic Botany), she has discovered that local squash species were independently domesticated in coastal Ecuador between 9,000 and 10,000 years ago, perhaps slightly predating squash domestication in the upland regions of Mexico.

Recently, evidence from microfossils has revealed that chili peppers were domesticated more than 6,000 years ago in South America. Starch grains of domesticated chili peppers differ in appearance from those of wild species. The starch grains of domesticated chili peppers have been preserved on grinding stones, ceramic shards of cooking vessels, and in soil sediments from archeological sites in Central America, South America, and the Bahamas, with the oldest sites in Ecuador.

Figure 11.5 Preserved corncobs from the Tehuacan Valley, Mexico. The oldest cob, on the left, is approximately 1 inch long.





Much attention has been focused on the early site of agriculture in the eastern forests of North America. On the basis of the latest evidence, the eastern half of what is now the United States and Canada was another New World center of plant domestication, developing independently at least four domesticated seed crops: sunflower, marsh elder, goosefoot, and wild gourd. These farming societies flourished for some 2,000 years before the arrival of maize and other domesti-cated crops from the Southwest in A.D. 1–200 ( fig. 11.4 ).

CHARACTERISTICS OF DOMESTICATED PLANTS Plants that have been domesticated are genetically distinct from their wild progenitors. Through the process of naturalselection (see Chapter 8), wild plants have evolved mecha-nisms that ensure their survival in the environment, but once a plant has been domesticated, traits are artificially selectedto suit human needs and do not necessarily have a survival value. In fact, some of these traits might be detrimental to sur-vival in the natural environment. For example, modern corn, with its ensheathing husks, cannot disperse its seeds; also, domesticated wheat and other cereals have fruiting heads that are nonshattering, a trait that limits seed dissemination.

Most wild grasses have shattering fruiting heads, which will break apart at a slight touch or breeze and scatter their seeds over a wide area. A recessive gene is responsible for a tough spike with a nonshattering head. It would be natural for early foragers to gather those seeds attached to the tougher spikes. When agriculture began, the seeds most easily gath-ered would be planted and so pass on the nonshattering trait. In 2006, researchers pinpointed the exact gene mutation in domesticated rice which codes for the nonshattering fruiting head. By comparing the DNA sequences of domesticated rice to its wild relatives with the shattering trait, researchers found a single gene on chromosome 4 with one difference in the nucleotide bases. The wild rice species had a G (guanine) which had been replaced by a T (thymine) in domesticated rice. After the researchers genetically engineered domesticated rice and restored the G, the shattering trait was also restored.

Likewise, early foragers would select for larger seeds, fruits, or tubers, and over time the domesticated varieties would become larger than their wild counterparts. For exam-ple, wild barley has two rows of grains while the domesti-cated varieties have six rows ( fig. 11.6 ). In fact, archeological evidence of six-row barley is indicative of agriculture at that excavation. Loss of seed dormancy is another general char-acteristic of domesticated plants. Seeds of most wild plants are dormant. For example, wild seeds formed at the end of autumn typically do not germinate immediately. Instead ger-mination is delayed via chemical means (hormonal control) or mechanical means (a tough seed coat) until the next spring when the environmental conditions are favorable for seedling growth and survival. Plant breeders continue to select for desired traits today, using traditional as well as more sophis-ticated genetic manipulations (see Chapter 15).

Concept QuizDomesticated plants are genetically different from their wild relatives.

The fruits of wild cherry trees are sour tasting, yet the domesticated varieties derived from wild populations produce deliciously sweet cherries. Explain the difference between wild and domesticated cherries by explaining the difference between artificial and natural selection.

CENTERS OF PLANT DOMESTICATION Within each area of the world where agriculture evolved, the native peoples developed indigenous crops for a staple food supply. Crops that were particularly suitable for agriculture slowly spread to surrounding regions as people traded with others or migrated to new areas, bringing their crops with them. This diffusion led to the emergence of principle crops associated with major centers of the world. In the Near East, wheat and barley were the dietary staples; in the Far East, rice; in Africa, it was sorghum and millet; in Mesoamerica, corn; and in South America, it was the potato and other root crops. As civilization continued to develop, trading and migration expanded the range of crops far from their origin, and today many crops are even more successful outside their native range. Potatoes, which became associated with the

Figure 11.6 Two-rowed wild barley (left) is contrasted with six-rowed domesticated barley (right).





Irish, are actually native to the highlands of Peru; coffee, actually native to the mountains of Ethiopia, is most fre-quently linked to Colombia and Brazil; and the tomato, so essential to Italian cuisine, was first domesticated in the New World. The agricultural harvest of the United States would be meager if limited to commercial crops of native origin such as blueberries, cranberries, sunflower, pecan, and maple syrup.

Pinpointing the exact origin of important crops has intrigued scientists for many years. The name most frequently associated with this endeavor is Nikolai I. Vavilov, a Russian botanist. Vavilov directed plant-collecting expeditions around the world and examined thousands of plants, looking for pat-terns of variation in crop plants and their wild relatives. He reasoned that areas that had the greatest diversity of a par-ticular crop would most likely be the center of origin for that crop. On the basis of his research from 1916 to 1936, Vavilov proposed eight centers of origin for the major domesticated plants, six in the Old World and two in the New World. Examples of crops known to have originated in these centers are indicated in Figure 11.7 . Vavilov’s life ended tragically in a Soviet gulag. Biology in the Soviet Union under Stalin was dominated by Trofim Lysenko, who rejected established genetic theory in favor of his own outdated views. Vavilov’s adherence to Mendelian genetics clashed with the established policies of the Soviet state, and he was sentenced to a Soviet prison camp where he died in 1943, a martyr to the cause of scientific freedom.

Recent work has expanded the number of centers and questioned Vavilov’s conclusions. Evidence suggests that although some crops have been domesticated more than once in different places, others did not originate where Vavilov indicated, and still others were developed over vast regions. For example, certain New World crops such as cotton and cas-sava appear to have been independently domesticated in both Mesoamerica and South America. This search for the origin of certain crops is even more important today as plant geneticists strive to improve the gene pool of domesticated plants by tap-ping the genetic resources of wild strains (see Chapter 15).

CHAPTER SUMMARY 1. The first human societies were based on a foraging life-

style, gathering wild plants and hunting animals for food. Archeological investigations have determined that the diet of Stone Age foragers was varied, especially in the variety of plants consumed. Studies on the diet and life-style of extant foragers, especially the !Kung San of the Kalahari Desert, reinforce the viewpoint that the foraging lifestyle more than satisfies the nutritional requirements yet allows time for activities not directed to food gather-ing and preparation.

2. The archeological record indicates that, at least in some parts of the world, certain groups began to shift from the nomadic, foraging lifestyle to the sedentary one of

Corn

Tomato

Dry bean

Peanut

Potato

Sugarbeet

Sunflower

Tobacco

Dry beanSorghum

Onion

Alfalfa

Grape

Cotton

Cotton

Strawberry

Strawberry

Almond

Wheat

Barley

Apple

Soybean

Rice

Orange

Sugarcane

Rye

Figure 11.7 Centers of origin as first defined by N. I Vavilov are indicated by the shaded areas. More recent work has shown that some crops were domesticated outside these areas or were domesticated independently in several regions.





agriculture. Many theories to explain this shift have been presented and discarded over the years, but the currently held view believes that the switch to agriculture was gradual. A prolonged transitional stage ensued in which groups formed settlements but sent out members to hunt and gather.

3. The earliest agricultural settlements, approximately 11,500 years old, have been found in the Far East along the Yellow and Yangtze River valleys. Sites in the Near East, in an area known as the Fertile Crescent, also docu-ment early agriculture. The New World dates from the Tehuacan and Oaxaca valleys of Mexico show that agri-culture started at approximately the same time.

4. Domesticated plants and animals are genetically different from their wild relatives because they have been shaped by artificial selection. Many of the traits, such as nonshat-tering fruiting heads, do not enhance a plant’s survival value but have been selected to suit humanity’s needs.

5. Because domesticated plants have been modified greatly from their wild ancestors after thousands of years of artificial selection, it has often been difficult to pinpoint their area of origin. Nikolai I. Vavilov laid the foundation for detecting the centers of origin of domesticated plants when he proposed eight centers, six in the Old World and two in the New.

REVIEW QUESTIONS 1. What has been learned about foraging societies of the past

by studying the !Kung?

2. Describe an early agricultural community in the Near East.

3. How do archeologists reconstruct diets of prehistoric peoples?

4. How have the theories about the origin of agriculture changed in recent decades?

5. What crops were domesticated in the New World?

6. You are an archeologist on a dig and discover in a cave the preserved seeds and fruits of a type of squash. These remains are dated to between 8,400 and 10,000 years old. What characteristics would you look for to determine whether this squash was a wild type, gathered by forag-ing, or a domesticated plant, cultivated in the fields?

7. A national seed company offers a reward of $10,000 to the first gardener who develops a pure white chrysanthe-mum. How would you go about breeding a chrysanthe-mum for its color? What is the underlying process and its mechanism of action?

FURTHER READING Balter, Michael. 2007. Seeking Agriculture’s Ancient Roots.

Science 316 (5833): 1830–1835.

Braidwood, Robert J. 1960. The Agricultural Revolution. Scientific American 203(3): 130–148.

Bryant, Vaughn M., and Glenna Williams-Dean. 1975. The Coprolites of Man. Scientific American 232(1): 100–109.

Diamond, Jared. 1998. Guns, Germs, and Steel: The Fates of Human Societies. W. W. Norton, New York, NY.

Diamond, Jared and Peter Bellwood. 2003. Farmers and Their Languages: The First Expansions. Science 300: 597–603.

Fritz, Gayle J. 1995. New Dates and Data on Early Agriculture: The Legacy of Complex Hunter-Gatherers. Annals of the Missouri Botanical Garden 82(1): 3–15.

Gilbert, Robert I., and James H. Mielke. 1985. The Analysis of Prehistoric Diets. Academic Press, Orlando, FL.

Harlan, Jack R. 1976. The Plants and Animals That Nourish Man. Scientific American 235(3): 88–97.

Harlan, Jack R. 1992. Crops and Man, 2nd Edition. AmericanSociety of Agronomy. Madison, WI

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