How did rats and mice originate? - briefly
Rats and mice belong to the Muridae family, having diverged from ancestral muroid rodents in Eurasia roughly 12–15 million years ago, after which they dispersed worldwide through natural migration and human activity. Their evolutionary lineage is traced through fossil records and molecular data that show a rapid radiation of species within this time frame.
How did rats and mice originate? - in detail
Rats and mice belong to the family Muridae, the most diverse rodent lineage, with over 700 species distributed worldwide. Molecular analyses of mitochondrial and nuclear DNA place the common ancestor of modern murids in the early Oligocene, roughly 30–35 million years ago. Fossil evidence from Eurasia shows early murids such as Pseudomys and Anomalurops exhibiting dental patterns that later gave rise to the characteristic gnawing incisors of contemporary species.
The diversification of murids accelerated during the Miocene (23–5 million years ago) as grassland habitats expanded. Climatic cooling and the emergence of open environments created ecological niches that favored small, omnivorous mammals capable of rapid reproduction. Adaptive radiation produced two major clades: the Rattini tribe, which includes the true rats (Rattus spp.), and the Mus genus, encompassing the common house mouse and related taxa.
Key morphological innovations underpinning this success include:
- Hypsodont molars with complex occlusal surfaces, allowing efficient processing of seeds and insects.
- A highly flexible jaw musculature enabling powerful gnawing.
- A shortened gestation period (≈ 20 days) and large litter sizes, supporting quick population turnover.
Biogeographic studies indicate that the ancestors of Rattus originated in Southeast Asia, later dispersing to Africa, Europe, and the Americas via natural rafting and, subsequently, human-mediated transport. Mus species likely arose in the Indian subcontinent, spreading eastward into East Asia and westward into Europe through similar pathways.
Recent genomic sequencing of multiple murid species confirms a rapid mutation rate, particularly in genes related to xenobiotic metabolism and immune response. This genetic plasticity has facilitated adaptation to diverse diets and environments, explaining the pervasive presence of these rodents in human settlements worldwide.