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The common house mouse is as iconic and as recognizable as a dog, cat or a horse. However, we know surprisingly little about its origins. New research has revealed that not only have these pests been around humans for much longer than previously thought, they also had to fight off a competing pest species.

The longest standing theory used to be that mice came into contact with humans after we discovered agriculture, because they would have access to our storages where they would find plenty of food. However, this is now disputed, and the contending theory is that wild mice began intermingling with humans from the very first moment that hunter-gatherers started building more permanent structures.

New evidence shows that this occurred about 15,000 years ago in the Levant, which is 3,000 years before humanity started using agriculture. It was around this time that the Natufian people transitioned from nomadic hunter-gatherers to a more sedentary type of organization, attracting two species of mice, the species that would become today the house mouse and another species known as Mus macedonicus. The two species competed for centuries until the house mouse eventually won out.

The scientists reached this conclusion using a new technique known as geometric morphometrics. This technique allowed the researchers to identify these ancient mouse fossils. They also studied tribes of people living in similar social organizations today, such as the tribes found in Tanzania and southern Kenya

Mice became a separate species about 100,000 years ago. They had to scout the landscape, looking for grains, insects and fruits. The species that would become the common house mouse of today was likely extremely rare, locked into brutal competition with other mice. However, all this changed as the human settlement started to play a role in the environment 15,000 years ago.

Initially, the relationship between humans and mice was commensal, meaning that one species benefited while the other was not affected neither positively, nor negatively. It was not until the introduction of agricultural activity that mice became a pest.

However, becoming the highly adapted house mouse that we know today was not easy for this species. The Natufian people were semi-nomadic, leaving settlements behind at various intervals, an activity which would have scattered the mice into the wild. On top of that, the species had to compete with short tail mice for dominance over the settlements.

Right as the semi-nomadic stage of the Natufian people came to an end, the house mouse comprised 80% of the total mouse population in the area. What made this particular mouse species so well suited to live with humans boils down to a couple of factors. The first would be the longer tail, which allowed these micr to escape capture and better navigate the human settlement. They were also better adapted to deal with the added stress of living among humans. Researchers also believed that they were less picky eaters, choosing the larger quantity but lower quality (for the mice at least) of food found in the settlements.

Since then, the mice spread from the Levant to Europe, in a process that likely took thousands of years, and from Europe they reached every other continent in the world in the last few centuries. Today, you will find mice wherever you find humans, but the relationship between the two species, while still mostly parasitic, is starting to pay off for humans thanks to laboratory mice, which have helped make tremendous strides in the scientific and medical fields.