Humans first tamed wild animals about 12,000 years ago. Soon, they found they could change their animals over time. They did this by controlling how the animals reproduced.
Breeding fast horses with other fast horses created even faster horses. The same trick worked with plants. Wheat, corn, potatoes, apples, rice—every plant that we eat has been bred to be more useful. Yet for years, nobody could explain how this process worked. Finally, in the late 1800s, scientists discovered the secrets of heredity—the passing of genes from generation to generation.
