The family that includes Old World mice, rats, gerbils, whistling rats, and many others , is the most diverse family of mammals in the world. With over 730 species this family makes up about 18% of all living mammals! Members of this family are native to Africa, Europe, Asia, Australia, and some oceanic islands. Some species have been introduced by humans throughout the world, including house mice and urban rats. Most members of this family look more or less mouse-like or rat-like but they live in all kinds of habitats, eat many kinds of things, and have many kinds of social systems. They are not only the most diverse (in terms of numbers of species) mammal family in the world, they are also exceptionally diverse in terms of how they make a living.