For most of their two and a half million years on Earth, human beings lived as hunter-gatherers or foragers, subsisting on wild plants and animals. It was only between ten thousand and four thousand years ago that scattered groups of people transformed a few dozen wild plant species into _______ crops. The grain, pulse (peas and beans), root, and melon/squash crops they produced remain the principal sources of plant food for humans and their tamed animals today.
