The experiences of these nomads passed down through generations allowed them to adapt to their varied environments, from the permafrost of the Arctic to the arid deserts of Australia. By 12,000 years ago, humans lived on every continent but Antarctica.
But the story of how humans lived would not be one of endless “moving on.” The earth and its weather was moving in the form of periodic ice ages. During an ice age, the climate becomes colder, and oceans’ levels fall as slow-moving masses of ice called glaciers form over the land. Then, about 18,000 years ago the last ice age gave way to a period of global warming. Within a few thousand years of the end of the last ice age, the climate in some parts of the earth led to an abundance of wild cereal grains. Nomadic groups began to settle, or in other words, stay put in these places because they provided a steady source of food.
Some nomads discovered that, beyond what grew naturally, they could create more food by domesticating certain plants. Domesticate means to change plants or animals to make them more useful to humans.
Farmers in present-day Central America learned to cultivate a wild grass called teosinte. Over thousands of generations, they cut away the protective branches of teosinte and replanted only the crops with the largest cobs. The result of that manipulation is what we call corn, a plant that is more nutritious than teosinte but is incapable of surviving without human intervention.