The house mouse, Mus musculus, is a successful mammalian species, thriving globally due to its close association with human civilization. It belongs to the order Rodentia, a diverse group accounting for nearly half of all mammal species. Tracing the mouse’s ancestry requires looking back tens of millions of years to a time when mammals began to diversify following a major global extinction event.
The Earliest Mammalian Ancestors
The history of mice begins with the emergence of placental mammals (Eutheria), which diversified after the mass extinction event that ended the age of dinosaurs 66 million years ago. These early Eutherians were small, shrew-like animals that survived and exploited newly available ecological niches. The lineage leading to mice is rooted in the superorder Euarchontoglires, a grouping established through molecular evidence.
This superorder contains two major branches: Euarchonta (including primates, colugos, and treeshrews) and Glires (encompassing the Rodentia and Lagomorpha orders). The common ancestor of this group is estimated to have existed 85 to 95 million years ago. This ancient split set the stage for the specialized development that distinguishes rodents from their closest relatives, such as rabbits and hares.
The Emergence of the Rodent Order
The transition to the first true rodents occurred roughly 56 million years ago in the Late Paleocene or Early Eocene Epoch. This transition involved a major evolutionary innovation. The order Rodentia is defined by a single, ever-growing pair of sharp incisor teeth in both the upper and lower jaws.
These incisors are rootless, possessing hard enamel on the front and softer dentin on the back, which allows them to self-sharpen through constant grinding. The absence of canine teeth creates a space called a diastema. Specialized masseter muscles power this dentition, attaching to the jaw and skull to maximize the mechanical advantage for gnawing. Although the earliest fossils were found in North America, the ultimate origin of Rodentia is believed to have been in Eurasia.
Tracing the Lineage to Modern Murids
After the emergence of Rodentia, the order diversified, leading to the suborder Myomorpha, which includes mouselike and ratlike rodents. Appearing in the Early Eocene, this group is distinguished by specific features of the jaw musculature and skull structure. Within Myomorpha, the path leads to the superfamily Muroidea, which contains Muridae, the largest mammalian family.
The family Muridae, containing the “true” mice and rats, originated in tropical Asia, possibly in the early Miocene. Its success is linked to rapid speciation events that produced a massive array of species across Eurasia, Africa, and Australia. Genetic and fossil evidence suggests the genus Mus, which contains the house mouse, was established six million years ago. Mus musculus is one of the most recent products of these ancient Asian radiations.
Global Spread and Adaptation
The house mouse’s global dispersal as a commensal species, living in close association with humans, is the final chapter of its evolution. Genetic studies suggest Mus musculus originated in Southwestern Asia, likely the Indian subcontinent or the Iranian plateau. The species began splitting into main subspecies, such as Mus musculus domesticus and Mus musculus musculus, between 110,000 and 500,000 years ago.
The house mouse became linked with human settlements around 12,000 years ago, coinciding with the rise of agriculture, which provided stable food and shelter. Following human migration and trade routes, the mice spread rapidly across the globe, particularly since the Neolithic period. The Western European subspecies (M. m. domesticus) was transported across the Atlantic by European colonizers. This relationship has driven rapid adaptation, allowing mice to thrive in diverse, human-dominated environments through parallel genetic changes in traits like metabolism and body size.