In the nineteen-fifties, the Green Revolution churned out so many cereal crops that the United States began giving food away; when its techniques were exported to the rest of the world, they defused the “population bomb.” In the sixties, the American-led Livestock Revolution vertically integrated the production of animal products, creating a parallel increase in the consumption of meat. By the seventies, big poultry companies were churning out so many chickens that they had to invent new products—chicken nuggets, chicken salad, chicken-based pet food. Large corporations bought up local producers of poultry, pork, and beef; feedlots grew to the size of fairgrounds; hen houses dwarfed neighborhood strip malls. Farms went from being small operations with an average of seventy chickens to factories housing thirty thousand birds. In the eighties, with the Blue Revolution, the industrial farming of fish expanded, too. From 1980 to 2018, the global production of animals for consumption grew about one and a half times faster than the world population.

Barns packed with animals are good places to breed pathogens. Monocultures, in which all animals are genetically similar, offer few speed bumps to transmission. “You got fifty thousand chickens in a barn,” Rob Wallace, the author of “Big Farms Make Big Flu,” told me. “They are all genetically the same and you are growing them for a turn-around time of six weeks. That is all food for flu.” Normally, pathogens evolve to be harmful but not deadly: they want to co-opt hosts without killing them, so that they can continue their spread. But, in the fast-paced world of an industrial hen house, where birds come and go quickly, pathogens select for the most virulent strains, no matter how deadly. Within the uniform predictability of modern agriculture, the unpredictable emerges.