When did the gray rat appear? - briefly
The species Rattus norvegicus first emerged in eastern Asia during the early 18th century, and by the mid‑1700s it had been introduced to Europe and subsequently to North America. Its spread was driven by maritime trade and urban expansion.
When did the gray rat appear? - in detail
The gray rat (Rattus norvegicus) originated in the temperate grasslands of northern China and Mongolia. Fossil remains dated to the early Pleistocene, about 1.5 million years ago, represent the earliest known specimens of the species. Molecular analyses of mitochondrial DNA indicate that the lineage diverged from its closest relatives roughly 1.2 million years ago, confirming a long‑standing presence in East Asia.
Archaeological sites in the Yellow River basin contain rat bones associated with Neolithic settlements, dating to around 10 000 years before present. These findings suggest that the species began exploiting human‑made environments shortly after the advent of agriculture, when grain storage provided a reliable food source.
The expansion beyond its native range occurred in several distinct phases:
- Medieval trade routes (12th–15th centuries): Sporadic introductions into the Middle East and parts of Europe via overland caravans.
- European maritime exploration (16th–18th centuries): Ships carried the animal to coastal ports in the Americas, Africa, and Oceania, establishing permanent colonies.
- Industrial revolution (19th centuries): Urbanization and improved sanitation created dense habitats, allowing the species to become the dominant commensal rodent in many cities.
Genetic studies of contemporary populations reveal low‑level admixture among lineages, reflecting repeated human‑mediated dispersal events. The modern global distribution, covering most temperate regions, is therefore the result of both ancient natural expansion in East Asia and relatively recent anthropogenic spread.
In summary, the gray rat first appeared in the Pleistocene epoch in northern Asia, entered human settlements during the early Neolithic, and achieved worldwide presence through successive waves of trade and colonization beginning in the medieval period and accelerating during the age of exploration.