Where do rats and mice come from? - briefly
Rats and mice descend from wild ancestors that have migrated into human settlements, spreading worldwide through natural movement and human‑facilitated transport such as cargo shipments. Their success stems from rapid adaptation to varied habitats and exploitation of food resources associated with human activity.
Where do rats and mice come from? - in detail
Rats and mice belong to the order Rodentia, family Muridae, which first diversified during the early Eocene, roughly 50 million years ago. Fossil records show that the lineage leading to modern Rattus species emerged in Southeast Asia, while the ancestors of Mus musculus originated in the arid zones of the Middle East and spread into temperate Europe.
The two most widespread species—Rattus norvegicus (brown rat) and Rattus rattus (black rat)—originated in the Chinese and Indian subcontinents, respectively. Mus musculus (house mouse) traces its earliest presence to the Levant region. Their expansion correlates with human activity: maritime trade routes, agricultural storage, and urban waste provide food and shelter, facilitating rapid colonization of new territories.
Key mechanisms of distribution:
- Seaborne transport: ships carried rodents in cargo holds and provisions, establishing populations on coastal ports worldwide.
- Agricultural spread: grain storage and processing created stable food sources, allowing colonies to flourish in rural areas.
- Urban commensalism: dense human settlements offered nesting sites and constant refuse, supporting high reproductive rates.
- Accidental release: scientific laboratories and pet trade occasionally introduced species into non‑native environments, where they escaped or were released.
Population dynamics rely on short gestation (≈ 21 days for mice, 22 days for rats), large litter sizes (up to 12 pups for rats, up to 10 for mice), and rapid maturation. These traits enable exponential growth when resources are abundant, reinforcing their ability to occupy diverse habitats ranging from tropical forests to arctic suburbs.
In summary, the contemporary global presence of rats and mice results from an ancient evolutionary origin in Asia and the Middle East, combined with centuries of human‑mediated dispersal through trade, agriculture, and urbanization. Their biological characteristics ensure continual adaptation and persistence across virtually all human‑influenced ecosystems.