How mice became house mice

A new paper from Thomas Cucchi and coworkers in Scientific Reports probes the early history of the house mouse: “Tracking the Near Eastern origins and European dispersal of the western house mouse”.

A quick taxonomy of house mouse subspecies:

Although often overlooked compared with commensal rats (Rattus rattus, R. norvegicus and R. exulans), this elusive mammal has been a much more successful invasive rodent, becoming almost as ubiquitous as H. sapiens. Originating in the Indo-Pakistan subcontinent and neighbouring Afghanistan and Iran, house mice differentiated during the Pleistocene climatic oscillations into three main Mus musculus subspecies (M. m. domesticus, M. m. musculus and M. m. castaneus). All these subspecies are human commensals, facilitating their long-distance colonization and ultimately their cosmopolitan range.

The authors frame their work as ultimately an inquiry into the domestication and spread of cats:

The earliest and most striking evidence of cat domestication comes from 9,500 cal BP in Pre-Pottery Neolithic (PPN) Cyprus. Its introduction onto the island is thought to be tied to the control of the proliferation of the house mouse populations, present on the island since the Early PPNB26. The appearance of the domestic cat in western European archaeological contexts during the Iron Age, around 3,000 years ago, is synchronous with the strong evidence for the house mouse biological invasion of western Europe. This co-dispersal of cats and house mice has also been mentioned in literary sources, describing the deliberate transport of domestic cats on ships to control rodent pests, inducing its worldwide distribution. This co-phylogeography supports the premise that understanding the house mouse’s origin and dispersal can lead to insights pertaining to the origin of domestic cats and their subsequent dispersal.

Honestly I think that the process by which species become commensal with people is even more interesting than domestication. Humans exert intentional control over domestication. Commensal animals adapt to human-created environments largely on their own with little or no intentional human selection. Many would argue that cats are commensal rather than domesticated, and that may well have been true for much of the early history of domestic cats. Global house mouse (Mus musculus) populations exist in human-created habitats and are specialists within them.

The paper is mostly a straightforward review of first appearance dates and range expansion of the house mouse across the Levant and southeastern Europe. It’s not a full history. The authors have done work to understand which mice were inhabiting pre-agricultural sedentary populations of the Levant, followed by the spread of those mice into the eastern Mediterranean more broadly.

Most interesting, the mice adapted to human settlements before people started keeping granaries:

The earliest commensal populations of M. m. domesticus found in Natufian sedentary settlements (14,500 cal BP) confirm that the impact of sedentism on ecosystems and the ecology of organisms (i.e. reduction of predation and competition pressures, climatic buffer etc) was the catalyst for the commensal relationship between mice and humans rather than the emergence of agriculture systems with large-scale grain storage, which emerged two millennia later. Nevertheless, M. m. domesticus was identified only in the largest, long-term Natufian settlements such as ‘Ain Mallaha in the Southern Levant and Mureybet in the Northern Levant between 14,500 and 12,000 BP. In smaller and shorter term Natufian sites in the Southern Levant, only the native mouse Mus macedonicus was identified. This pattern suggests that dense human occupation in large open air settlements was the prerequisite for M. m. domesticus to eventually outcompete other potential anthropophilous rodent like M. macedonicus from the Natufian ecological niche.

That suggests that the protection that human settlements provided from other nonhuman predators may have been more important than human-accumulated food resources that mattered to mice. Sure, there was plenty of trash to eat around human settlements even without large-scale grain storage. But a reduction in predation from raptors and small carnivores created a very attractive environment for a small rodent.