The two rat species you’re most likely to encounter, the brown rat and the black rat, both originated in Asia but from different regions. Brown rats trace back to northern China and Mongolia, while black rats originated in India. Both species spread across the globe by hitching rides with human trade and migration, arriving in Europe centuries ago and eventually reaching every continent except Antarctica.
Brown Rats: From Northern China to Everywhere
The brown rat is the most common rat species worldwide. Fossil and genetic evidence places its ancestral range in northern China and Mongolia, where it evolved as a cold-hardy species well suited to harsh climates. The broader genus Rattus originated and diversified across eastern and central Asia, but the brown rat specifically came from the northern part of that range.
For thousands of years, brown rats lived as wild animals in their native habitat. Their shift to living alongside humans, feeding on our food stores and sheltering in our buildings, came relatively late. Brown rats didn’t reach Europe until the 1700s. The French naturalist Buffon, writing in Paris in 1760, noted that the brown rat had appeared in the area only “nine or ten years” earlier. The earliest confirmed brown rat in North America dates to 1760, recovered from the wreck of a French ship called Le Machault in New Brunswick.
Despite their common name “Norway rat,” these animals have nothing to do with Norway. That name was coined around 1731 based on a mistaken belief that rats arrived in Britain on ships from Scandinavia. Norway didn’t even have documented brown rat populations until 1762. Naturalists recognized the name as wrong within decades, but it stuck anyway.
Black Rats: India’s Gift to the World
Black rats took a different path. Archaeological and genetic evidence points to India as their homeland, with their earliest commensal relationship with humans developing around 5,000 years ago alongside the Indus Valley civilization in northwestern India. That civilization, one of the earliest in South Asia, created the dense settlements and food storage systems that gave black rats a reason to move in with people.
Genetic studies show that black rat populations on India’s east coast are the most ancestral, but it was along the west coast that the species became fully commensal and eventually spread globally. India’s position along major maritime trade routes made this dispersal almost inevitable. Traders sailing from India’s coasts carried black rats to ports across the Indian Ocean and beyond.
How Rats Spread Across Europe
Black rats arrived in temperate Europe in two distinct waves, both tied directly to economic activity. The first wave accompanied the Roman Empire’s northward expansion during the first centuries BCE and CE. Black rat remains from this period are found throughout Roman territory but rarely beyond its northern borders, suggesting the rats depended on the Roman system of dense settlements connected by roads, rivers, and maritime shipping routes. When goods moved, rats moved with them.
After the Roman Empire collapsed, black rat populations appear to have declined and possibly contracted in range. The second wave came during the medieval period, starting in the 8th to 10th centuries CE, as European economies rebuilt and long-distance trade resumed. This medieval reintroduction brought black rats back into northern Europe, where they would remain the dominant urban rat for centuries until brown rats arrived and largely displaced them.
Brown rats, arriving in Europe in the 1700s, spread rapidly. Their larger size, aggressive temperament, and comfort in colder climates gave them an edge over black rats in most environments. Within a few generations, brown rats became the dominant species in cities across Europe and North America. Black rats retreated to warmer climates and port cities, where they remain more common today.
Why Rats Thrive Near Humans
Both species are commensals, meaning they live off resources provided by human activity without being invited. They exploit food, water, and shelter that come with human settlements. In cities, rats nest in warm, enclosed spaces: behind appliances, inside walls, in attics, and in underground burrow systems near buildings. They don’t need to travel far. A rat colony typically stays close to reliable food and water sources.
This relationship with humans is what made rats so successful. A wild rat living without human resources typically survives less than a year. Domesticated pet rats, bred from brown rat stock, live two to four years in captivity. The difference reflects how much wild rats depend on a constant, dangerous hustle for food and shelter, and how dramatically their prospects improve with reliable resources.
From Pests to Pets
The history of domesticated “fancy” rats traces back to Victorian England. Jack Black, the official rat catcher to Queen Victoria, was known for breeding unusual color variations of brown rats. He sold these fancy rats as pets to English ladies, turning a pest control business into an early exotic pet trade. Japan had an even earlier tradition of breeding rats for unique coat colors and patterns during the 1600s and 1700s.
Formal domestication for scientific research began in Europe in the early 1800s and expanded in North America through the mid-1800s to early 1900s. Every lab rat and pet rat alive today descends from wild brown rats captured during these breeding programs. Despite thousands of generations in captivity, they remain the same species as the brown rats living in city sewers, just selectively bred for temperament and color.
Their Current Range
Brown rats now live on every continent except Antarctica. Black rats occupy a similarly vast range but concentrate more heavily in tropical and subtropical regions. In most temperate cities, the brown rat is the species you’ll encounter. In warmer coastal areas and parts of the tropics, black rats are still the dominant species. Both continue to spread into new territories wherever human development creates opportunity, following the same pattern that carried them out of Asia thousands of years ago.