Wheat, maize, rice ... repeat. Those three starchy plants provide about half of all the calories we consume. What's more, of the 12,000 plant species that can be used for human food, only about 150 are cultivated. And that heavy reliance on a limited number of crops poses a serious risk when it comes to our food security. We can look back to the devastation of the Irish potato famine to see the importance of crop diversity. A million people died because a blight killed just one species of potato—the Irish lumper.