Jack R. Harlan conceived the prevailing concepts of how the activities of human societies have shaped the evolution of crops used for food, feed, and fiber. Harlan collected and introduced over 12,000 accessions of plants into the United States. The world food supply now depends largely on only 12 to 15 plant species. Erosion of diverse gene sources from ancient landraces continues and more effective use needs to be made of germplasm collections in our gene banks.