How did domestic rats appear? - briefly
Domesticated rats derived from wild species such as the black rat (Rattus rattus) and the brown rat (Rattus norvegicus) that began exploiting human grain stores and shelters in early agricultural societies. Over centuries, commensal relationships and selective pressures favored individuals tolerant of human proximity, producing the stable, synanthropic populations observed today.
How did domestic rats appear? - in detail
Domestic rats originated from wild populations that began exploiting human settlements thousands of years ago. The two species most frequently associated with domestication are the black rat (Rattus rattus) and the brown rat (Rattus norvegicus). Both species are commensal rodents that found abundant food and shelter in granaries, warehouses, and later in urban environments.
Archaeological evidence shows that black rats entered the Mediterranean region during the Bronze Age, attracted by stored grain. Their presence is documented in Egyptian tombs, Greek pottery, and Roman refuse pits. By the early medieval period, black rats had spread throughout Europe, traveling aboard merchant vessels that linked ports across the Atlantic and the Indian Ocean. The brown rat, native to the steppes of Central Asia, arrived in Europe later, during the 18th‑century expansion of trade routes. Its adaptability to colder climates facilitated its rapid replacement of the black rat in many northern cities.
The transition from wild to domestic status involved several factors:
- Food availability – human grain stores provided a reliable resource, reducing the need for foraging.
- Shelter proximity – structures such as barns and cellars offered protection from predators.
- Human-mediated transport – ships and caravans unintentionally carried rats across continents.
- Selective pressures – individuals tolerant of human presence reproduced more successfully within settlements.
Over successive generations, rats that were less fearful of humans and more capable of thriving on processed foods became predominant. This process did not involve intentional breeding; instead, it resulted from natural selection within anthropogenic environments. The outcome is a population of rodents that exhibit reduced wariness, altered reproductive cycles, and a close ecological association with human activity.
Modern domestic rats, used in laboratories and as pets, derive from these commensal lineages. Selective breeding programs have emphasized traits such as docility, coat color, and size, but the foundational relationship between rats and humans traces back to the early exploitation of stored food resources and the unintentional global dispersal facilitated by trade. «The domestication of rats illustrates how human economic activities can shape the evolution of animal species without deliberate intervention».