We have increased our population to the level of 7 billion and beyond. We live at high densities in many cities. We have penetrated, and continue to penetrate, the last great forests and other wild ecosystems of the planet. We cut our way through the Congo, through the Amazon, through Borneo. We shake the trees, figuratively and literally, and things fall out. We kill and butcher and eat many of the wild animals found there. We settle in those places, bringing in our domesticated animals. We multiply our livestock as we've multiplied ourselves, under conditions that allow them to acquire infections, to share them with one another, and to infect humans. We export and import livestock across great distances and at high speeds.

We travel, moving between cities and continents even more quickly than our transported livestock. We stay in hotels where strangers sneeze and vomit. We eat in restaurants where the cook may have butchered a porcupine before working on our scallops. We visit monkey temples in Asia, live markets in India, picturesque villages in South America, bat caves in East Africa – breathing the air, feeding the animals, touching things, shaking hands with the friendly locals. And then we jump on our planes and fly home.