A combination of habitat loss and hunting has reduced rhino numbers significantly in the past 30 years from around 500,000 to less that 18,000. This has left all species of rhino extremely endangered. Humans have hunted rhinos extensively because nearly all parts of the animal have been used in folk medicine. The most prized part of the rhino is its horn, which has been used as an aphrodisiac, fever-reducing drug, dagger handle, and as a potion for detecting poison. Rhinos rank among the most endangered species in the world.