How long have rats existed? - briefly
Fossil evidence shows rat-like rodents first appeared in the Oligocene epoch, roughly 23 million years ago. Modern species such as the brown and black rat evolved within the past few million years.
How long have rats existed? - in detail
Rats belong to the murid family, which originated in the early Oligocene, approximately 34–30 million years ago. Fossil genera such as Diatomys and Pliomys illustrate the early diversification of murine rodents, establishing the lineage that would later give rise to modern rats.
The genus Rattus itself appears in the fossil record during the late Miocene, about 10–12 million years ago. Specimens attributed to Rattus have been recovered from sedimentary deposits in Southeast Asia, indicating that the group emerged in the region that currently hosts the highest species richness.
Two species dominate the present‑day distribution:
- Rattus norvegicus (the brown rat) – first documented in archaeological layers dating to the early Holocene, roughly 4 000 years ago, and subsequently spread worldwide through human activity.
- Rattus rattus (the black rat) – evidence from Mediterranean sites shows presence by the early second millennium BC, coinciding with ancient trade routes.
Molecular clock analyses, calibrated with these fossil dates, estimate the split between R. norvegicus and R. rattus at 1.5–2 million years ago. This timing aligns with climatic fluctuations of the Pleistocene that promoted rapid speciation within the genus.
In summary, rat ancestors have persisted for tens of millions of years, with the modern genus emerging in the Miocene and its most widespread species establishing themselves within the last several thousand years.