The plants we grow en masse to sustain humanity do not arise from some mystical “all natural” process. They are chosen, bred, altered and cultivated by human beings, for human beings, and mostly it works. But the plants of unnatural agriculture still have natural enemies. They kill our food, and often humans suffer.
One particularly vicious enemy is a microbe called Phytophthora infestans. Technically it is an oomycete, a sort of fungus or mildew that blows on the wind and clings to the mist and dearly loves the plants of its native America, and one in particular that we call potato. Phytophthora infestans, also known as late blight, followed the ancestors of the potato to the islands off northern Europe, where potatoes grow well and are a vital source of calories for millions. But Phytophthora infestans thrives in the cool, moist air, and finds a ready host in the potato fields. The pathogen from one infected plant or tuber can turn an entire year’s crop into putrid, stinking, inedible mush in a matter of days. It has happened, and in 1840s Ireland thousands starved, and thousands more migrated to lands where they might find sustenance, and chances are good one of them was your ancestor.