The 50 animals include the horse, dog, rat, whale, reindeer, beaver, flea, leech, dodo, falcon, oyster and shark. These creatures, great and small, have played central roles in the evolution of humankind, but they have remained at the periphery of our understanding of history. Whether it is an advancement in scientific knowledge, a trade war, disease and death, battles won and lost, or encounters with explorers in unknown lands, these animals have changed the course of history.