Members of a common species of rat known worldwide. The brown rat may be brown or gray. As the black rat, the brown rat has exploited human food resources, moved all over the world with humans, and is often considered a pest because it has killed small livestock and native species, and spread certain diseases among humans; it has also been used in laboratories worldwide for medical, genetic, and basic biological research. It is thought to have originated in northern China; it is now the dominant rat in Europe and much of North America.
