We live at the crossroads of three global megatrends, three barreling and intertwined juggernauts of modernity. The first is the massive migration of humanity to the world’s cities. I grew up in a small town, walking deer trails beneath the shade of maples and oaks. Now I live with my kids in a city where the path beneath our feet is ever more likely to be paved. My story is our story. By 2050, two-thirds of all humans on Earth will live in cities.

The second is the loss of biodiversity. Species are disappearing, both from the places where we live and from the earth as a whole. If our hairy ancestors were to visit our cities and suburbs, they would wonder how the escalators work, but they would also question where the plants and animals have gone. What have we done with all the birds? Some, like the Carolina parakeet, are just gone. Others live on, but at a distance—geographically removed from our daily lives, far away from the majority of people.