Human survival depends on an extraordinarily complex dance with animals. From the bees whose pollinating habits give us much of our food supply to the primates who testify to the power of evolution, from the animals that transmit diseases to humans to those that contribute to therapeutic research, our lives are completely intertwined with the millions of other species inhabiting Earth. These delicate relationships are being transformed in an era of mass extinction and biodiversity loss, upending agriculture, increasing transmission of infectious diseases, modifying the gut microbiome that preserves immune function, and diminishing the benefits of experiencing nature.