The evolution of agriculture is illustrated as:

1. 8000 B.C.: Inhabitants of the Middle East begin to farm wheat. The change from gathering a crop in the wild to farming it eventually contributes to the rise of one of the earliest Middle Eastern civilizations.
2. 7000 B.C.: Chilies and avocados become important additions to the diets of Mesoamerican people. Chilies are used for flavoring foods, and avocados provide vitamins and oils.
3. 5500 B.C.: Barley is grown in the Nile Valley of Egypt. About 2000 years later, farming settlements are united throughout the Nile Valley, and Egyptian culture flourishes.
4. 5000 B.C.: People in central Mexico grow a form of corn called maize. Early corncobs are only about an inch long and have a few dozen kernels. The ancestor of corn was a wild grass called teosinte.
5. 4500 B.C.: Rice farming becomes well established in southern China, southeast Asia, and northern India. Rice farming spreads widely from these regions, and rice later becomes a major Chinese export.
6. 3500 B.C.: The potato is farmed in the Andes Mountains of South America. Early Andean farmers eventually produce hundreds of different varieties of potatoes by growing them on irrigated terraces built on mountain slopes.