What do plants, snakes, molds, marine sponges, and cone snails have in common? They have helped develop medicines that save human lives. Biodiversity -- the variety of life on Earth -- is key to human survival. But plants, animals, and microorganisms are disappearing at unprecedented rates. What impact will this have on human health? Find out in this Earth Focus special report produced in collaboration with the Center for Health and the Global Environment, Harvard Medical School.