Surviving primarily on potatoes, the Irish more than doubled their population between 1754 and 1845, when the potato famine showed up and ruined everything. And it wasn't just Europe. Manioc, or cassava, is a New World plant with roots that provide more calories than any other plant on Earth, provided they are properly processed, otherwise they're poisonous. Manioc is so prevalent in Africa that many Africans swear the plant is native to the continent, but it isn't. Nor are sweet potatoes, and while New World grains never replaced rice in Southeast or East Asia, the sweet potato is so common that it is known as the poor person's staple in China. Even in Japan, the tomb of the farmer who is reputed to have first brought them to the islands is known as the Temple of the Sweet Potato. And it's also worth noting that corn, while it may not feature prominently in European diets, has been the central source of food for animals in Europe for centuries.