This astonishing graphic from National Geographic shows the sharp decrease in seed variety over the past hundred years. Take a look:
Seeds vanished because farmers found they got higher yields and more protection against drought and blight with other varieties. However, this narrowing of crop diversity has been shown to reduce the ability of crops to fight off certain kinds of blight. Entire yields can be wiped out because of this genetic uniformity. If there’s a fungus particular to, say, one variety of grape, and almost everyone is planting that type of grape, vast amounts of food can be lost. It’s happened before, and with farmers planting only 12 types of corn, rather than 300, it can happen again.
h/t Sean Dailey, editor of the wonderful Gilbert.