Sharks lose teeth all their lives, replacing them in a kind of endless rotating Rolodex, while humans, of course, get only our two sets. Beavers’ teeth, notoriously, grow all their lives and have to be worn down to prevent injury. Sharks lose teeth all their lives, replacing them in a kind of endless rotating Rolodex, while humans, of course, get only our two sets. Beavers’ teeth, notoriously, grow all their lives and have to be worn down to prevent injury. Plants & Animals Molecular & Computational biology Phys.org – latest science and technology news stories