The domesticated brown rat (Rattus norvegicus) originated in northern China, where its ancestors thrived in diverse environments thanks to their exceptional adaptability and prolific breeding capabilities. From this region, brown rats embarked on a remarkable journey of migration, primarily facilitated by expanding trade routes and human exploration.

As merchants and explorers traveled across continents, rats often accompanied them aboard ships, thriving in cargo holds where ample food supplies ensured their survival. This maritime migration was instrumental in establishing rat populations in Europe, Africa, the Americas, and other parts of the world. Their ability to exploit human settlements for food and shelter enabled them to quickly colonize urban centers, rural areas, and a wide range of habitats, from bustling ports to agricultural lands.

The Industrial Revolution further accelerated the spread of brown rats, as increased urbanization and global trade provided more opportunities for these resilient rodents to establish themselves in new regions.

In Europe, cities like London and Amsterdam became hotspots for rat infestations, while European settlers introduced rats to North America, Australia, and Africa through ships and inland migration. Modern transportation methods, including trains and airplanes, have continued to facilitate their global dispersion, making brown rats one of the most widespread and successful rodent species on the planet.