History of Agriculture
Agriculture is the raising of domesticated animals and the planting, cultivation, and preservation of crops. Agriculture entails selective breeding of organisms with combinations of inherited characteristics that benefit humans (and not necessarily the organisms themselves), and so these practices have over time greatly influenced the course of evolution of these animals. Agriculture arose thousands of years ago in different parts of the world. The steps were similar in different places, but the types of organisms that were raised or cultivated differed. Underlying all of agriculture is human control of the environment.
From Hunting and Gathering to Intentional Intervention
Preparing a feast today is as easy as visiting the local supermarket, farm stand, or garden. However, fifteen thousand years ago, conditions were quite different. Isolated bands of people hunted and gathered on the parts of the earth not covered in ice, seeking wild game and edible plants. They had to find food, or starve.
Cultivation of plants may have arisen accidentally. According to the "dump heap hypothesis," wandering peoples discarded remains of plant foods in piles in cleared areas, then returned to the sites and discovered that the same types of plants they had eaten the year before grew again. Eventually, people connected the leaving of seed one season to finding of edible plants the next. Farming began when people intentionally saved and planted seeds of their favorite plants.
By selecting characteristics that make a plant a good crop, early farmers altered the genetic makeups of plant populations. Corn, for example, is a product of human intervention. Corn's ancestor, a grass called teosinte, had small ears with sparse kernels. As humans selected teosinte ears bearing the most plump kernels, they gradually edged evolution towards forming a new species, corn. A reminder today of this ancient intervention is that the jackets formed by the leaves covering an ear of corn (husks) are so tight that the plant cannot naturally release its seed. Other plant species were also changed by humans selecting variants that held onto seeds more tightly, a trait that would not benefit a plant in the wild.
Multiple Origins of Agriculture
Some of the earliest archeological evidence for agriculture comes from the Yellow River region of China, where the people raised rice and millet some fifteen thousand years ago. By thirteen thousand years ago, when warmer and wetter weather followed the end of the Pleistocene ice age, people in the Fertile Crescent, an area that today includes Iran, Iraq, Turkey, Syria, Israel, and Lebanon, cultivated wild grasses, which were the ancestors of barley and emmer and einkorn wheat, as well as lentils and chickpeas. The fields of grasses supported grazing animal populations.
Striking evidence of early agriculture is a ten thousand-year-old farming village in Jericho in the Jordan Valley built over the remains of a hunter-gatherer settlement. The farm was larger and supported more people, and included permanent homes and evidence of irrigation, including walls to hold back floods and ditches. Barley flourished in nearby fields.
By eight thousand years ago, farming settlements and villages ringed by crop fields had spread from the Middle East to Eastern Europe. People raised wheat, barley, legumes, goats, sheep, pigs, cattle, and many other species. By seven thousand years ago, people in central Europe and the western Mediterranean region were actively farming, and by four thousand years ago, the change came to the British Isles. Tombs, mummy wrappings, and paintings and hieroglyphics from Assyria and Egypt from this time herald a diet, at least among the well-to-do, that included figs, dates, grapes, olives, pomegranate, and several cereals. Meanwhile, agriculture was spreading in the Americas. By eight thousand years ago, people there were eating kidney beans, peanuts, lima beans, cocoa, avocados, pumpkins, squashes, tomatoes, chili peppers, and corn. Potatoes were a staple in settlements in the Andes Mountains in South America about four thousand years ago. On the African continent, cassava, yams, coffee, cotton, millet, and sorghum were among the first crops, grown about five thousand years ago.
Modern Agriculture and Biotechnology
The work of Charles Darwin and Gregor Mendel in the late nineteenth century, in evolution and genetics, respectively, revealed the biological basis of the selective breeding that is agriculture. Cultivation approaches could therefore become more directed. For example, in the early twentieth century, George Shull, at the Station for Experimental Evolution in Cold Spring Harbor, New York, crossed highly inbred strains of corn, and produced very robust hybrids . Use of hybrids ushered in a new era in agriculture, with many fields planted with the same strains of crop plants ( monocultures ). But this set the stage for disaster, such as arrival of a pathogen to which all of the plants were equally vulnerable. In the twenty-first century, farmers plant several varieties of the same crop to avoid the weakness of monocultures.
Traditional agriculture selects valuable variants among individual organisms, and breeding is between members of the same or very closely related species. Conventional breeding therefore mixes up many traits at a time. In contrast is agricultural biotechnology, in which addition or modification of specific genes creates valuable variants. Specifically, a transgenic plant or animal has an added gene in each of its cells. The transgene can come from a different type of organism, which is possible because all species use the same genetic code to manufacture protein . To return to the example of corn, plants that are transgenic for a gene from the bacterium Bacillus thuringiensis produce a protein that kills certain caterpillars, including the devastating European corn borer. Use of such "bt corn" enables a farmer to avoid using chemical pesticides, but has potential consequences of its own, such as promoting selection of borers resistant to the poison, and harm to nearby insect populations.
Agricultural biotechnology began in the 1970s, and people in the United States have been eating genetically modified foods since the mid-1990s. The goals of agricultural biotechnology are the same as traditional agriculture: improved appearance, flavor, and nutritional content of foods, and ease of cultivation.
Brintnall Simpson, Beryl, and Molly Conner Ogorzaly. Economic Botany: Plants in Our World, 3rd ed. New York: McGraw-Hill Higher Education, 2000.
McCully, Kilmer. "The Significance of Wheat in the Dakota Territory, Human Evolution, Civilization, and Degenerative Diseases." Perspectives in Biology and Medicine 44, no. 1 (Winter 2001): 52–61.
Smith, Bruce D. The Emergence of Agriculture. New York: Scientific American Library, 1995.