In the last 500 years, nothing about people—not their clothes, ideas, or languages—has changed as much as what they eat. The original chocolate drink was made from the seeds of the cocoa tree (可可树) by South American Indians. The Spanish introduced it to the rest of the world during the 1500’s. And although it was very expensive, it quickly became fashionable. In London, shops where chocolate drinks were served became important places. Some still exist today. The potato is also from the New World. Around 1600, the Spanish brought it from Peru to Europe, when it soon was widely grown. Ireland became so dependent on it that thousands of Irish people starved when the crop failed during the Potato famine (饥荒) of 1845— 1846, and thousands more were forced to leave their homeland and move to America. There are many other foods that have traveled from South America to the Old World. But some others went in the opposite direction. Brazil is now the world’s largest grower of coffee, and coffee is an important crop in Colombia and other South America countries. But it is native to Ethiopia, a country in Africa. It was first made into a drink by Arabs during the 1400’s. According to an Arabic legend, coffee was discovered when a person named Kaldi noticed that his goats were attracted to the red berries on a coffee bush. He tried one and experienced the "wide-awake" feeling that one-third of the world’s population now starts the day with.

Thousands of Irish people starved during "the Potato famine" because ______.