A Prehistory of South America: Ancient Cultural Diversity on the Least Known Continent

5. Origins and Consequences of Agriculture in South America

132 Chapter 5: Origins and Consequences of Agriculture in South America Figure 5.2 Petroglyph depicting humans and camelids morphology or genetics of plants and animals occur as a result of human interventions , often by artificially selecting species that have certain qualities (a larger fruit or a less toxic tuber). This may result in new domesticated species. Second, there are several terms relating to human involvement with plant or animal species (figure 5.2). Wild resources can be managed—for example, setting controlled burns to create open browse for game animals—without resulting in domesticated species . Cultivation is the “intentional preparation of the soil”; this may involve either wild or domesticated species. Finally, three terms reflect the engagement of human societies with domesticates. Farming refers to the use of domesticated animals , plants, or both for food, fibers, transport, and other purposes. Agriculture refers to an economic system that is largely dependent on farming domesticated animals and plants, although hunting and gathering may continue to be pursued. Agrosystem refers to a particular set of domesticates and agricultural practices. In South America, the number of domesticated plants far outnumbers the number of domesticated animals.4 Only a few animals were originally domesticated in South America: the llama, alpaca, Muscovy duck, and guinea pig (figure 5.3, figure 5.4). In contrast, a variety of plants first domesticated in South America became widespread cultigens, many of extraordinary importance to modern agriculture and commerce, including the potato, cotton, and specific varieties of beans, yams, squash, and chilies. For this reason, investigating the origins of South American 133 Chapter 5: Origins and Consequences of Agriculture in South America Figure 5.3 Guinea pigs in a market in Ecuador agriculture requires the study of various plant remains, a field referred to as paleoethnobotany or archaeobotany.5 Macrobotanical remains refer to the large items—seeds, stalks,tubers,and charcoal—that are evidence of plant use visible to 134 Chapter 5: Origins and Consequences of Agriculture in South America the naked eye. Microbotanical remains refer to microscopic evidence of ancient plants, which take different forms. Palynology is the study of pollen grains, minute specks of genetic material , each with a hard exterior surface—the exine.6 The exine is extraordinarily durable, often lasting thousands of years. Further, pollen exines exhibit radically diverse exterior geometries that are consistent at the family or genus levels, and these distinctive microscopic morphologies allow for the identification of ancient Figure 5.4 Guinea pigs on a stick, Ecuador 135 Chapter 5: Origins and Consequences of Agriculture in South America pollens. Pollen is dispersed in various ways—blown by the wind, carried by bats or birds that feed on the plant’s fruits, or simply falling nearby. Different factors affect the preservation of pollen. Highly alkaline soils may chemically degrade the pollen grains. Some bacteria and fungi feast on certain pollens. Floods or seasonal downpours can erode the pollen. The best locations for pollen sampling are often relatively calm ponds or bogs, where the pollen settles into the sediments and can be sampled and extracted in stratigraphic cores.Pollen is also recovered from other archaeological sources,such as excavated caves and rock shelters,the surfaces of ancient storage pots or metates, and even coprolites (desiccated feces). Palynological data can indicate changes in vegetation communities,including changes caused by farming, variations in plant use, or patterns of human consumption. Phytoliths are another class of plant remains, minute accretions of soluble silica absorbed by plants from the groundwater and earth and accumulated in the leaves and stalks (figure 5.5).7 Similar to pollens,phytoliths exhibit distinctive surface geometries associated with different plant species, although phytoliths from a single species can vary depending on whether they were formed in stalks, leaves, or fruit. Additional measurements ,such as maximum and average length and width,are needed to identify phytoliths. For example, domesticated plants often have larger phytoliths than their wild relatives, as wild members of the squash family (Cucurbita) are smaller than 100 microns (0.1 mm), while phytoliths from domesticated species are larger. In a square centimeter of hard squash rind, several thousand phytoliths can occur, making them an abundant—but extremely small—source of paleobotanical data. In archaeological contexts, soil samples are collected and submitted for analysis, in which the phytoliths are bathed in a series of chemical washes to separate them Figure 5.5 Selection of phytoliths and starch grains from the...