Plants Agriculture and Human Population

Starting about eleven thousand years ago (five million people), humans began to cultivate such plants as barley, lentils, wheat, and peas in the Middle East—an area that extends from Lebanon and Syria in the northwest eastward through Iraq to Iran. In cultivating and caring for these crops, early farmers changed the characteristics of these plants, making them higher yielding, more nutritious, and easier to harvest. Agriculture spread and first reached Europe by approximately six thousand years ago.

Agriculture might also have originated independently in Africa in one or more centers. Many crops were domesticated there, including yams, okra, coffee, and cotton. In Asia, agriculture based on staples such as rice and soybeans and many other crops such as citrus, mangos, taro, and bananas was developed. Agriculture was developed independently in the New World. It began as early as nine thousand years ago in Mexico and Peru.

World and Urban Population Growth, 1950-2020

1950 1960 1970 1980 1990 2000 2010 2020

^ Total world population Urban population

Note: The world's population passed 6 billion in the year 2000.

Sources: Data are from U.S. Bureau of the Census International Data Base and John Clarke, "Population and the Environment:

Complex Interrelationships," in Population and the Environment (Oxford, England: Oxford University Press, 1995), edited by Bryan Cartledge.

Christopher Columbus and his followers found many new crops to bring back to the Old World, including corn, kidney beans, lima beans, tomatoes, tobacco, chili peppers, potatoes, sweet potatoes, pumpkins and squashes, avocados, cacao, and the major cultivated species of cotton.

For the last five to six centuries, important staple crops have been cultivated throughout the world. Wheat, rice, and corn, which provide 60 percent of the calories people consume, are cultivated wherever they will grow. Other crops, including spices and herbs, have also been brought under cultivation.

The growing population has changed the landscape, distribution, and diversity of plants dramatically. Clear-cutting and deforestation have driven many species (both plant and animal) to extinction. Relatively little has been done to develop agricultural practices suitable for tropical regions. As a result, the tropics are being devastated ecologically, with an estimated 20 percent of the world's species likely to be lost by the mid-twenty-first century.

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