Sunny rays penetrate the canopy of an Indonesian rain forest on Nias Island. Rain forests are among the Earth’s most biologically diverse habitats. Their fauna and flora are precious for their own sake but can also aid humans. Rain forest plants, for example, produce chemicals to combat insects and disease that have led to the development of many beneficial drugs. But rain forests around the world are being deforested at alarming rates—even as many of their species and secrets remain unknown to humans.