The history of human migration patterns contains plenty of mysteries. How did early people find their routes to new places like Europe and Southeast Asia? When did populations establish on remote islands? How did modern humans and Neanderthals interact? However, we tend to assume that it is only people who have rich and varied histories. A new study serves to remind us that many species have joined the circuitous path to current settlement patterns.

House mice, Mus musculus domesticus, have some interesting stories of their own. The past is coming to light through the study of mitochondrial DNA. It seems that some mice across Ireland, Scotland, and Wales can look to Norway for their ancestry. It’s likely that these mice were introduced by Vikings in the 11th and 12th centuries.

While there were mice already present in the British Isles, the Scandinavian relatives thrived as settlements grew in more remote areas. House mice populations are dependent on food sources, provided by grain gathered for human consumption. Vikings may have established the first northern settlements populous enough to support these mice. The remaining, non-Viking, mice share more genetic characteristics with German mice. Waves of human migration may have brought mouse passengers from different locations as early as the Iron Age (7th century BCE to 5th century CE).

In fact, the house mouse is thought to have originated in central Asia but is now found worldwide. It is one of the most widespread and successful mammals, able to thrive opportunistically along with humans. Not only do mice live around homes, buildings, and other human structures, but they can also thrive in fields, rock crevices, and underground burrows.

Mitochondrial DNA (mtDNA) is separate from other genetic material. While most DNA is found chromosomes in a cell’s nucleus, mtDNA is in a cell’s mitochondria (structures responsible for cellular respiration, where energy is produced from sugar). The information in mtDNA is typically related to mitochondrial function and protein synthesis. It is crucial to basic processes, and, in humans, there are medical conditions related to mtDNA mutations. These include certain cancers, different neuropathies, retinitis pigmentosa, and other disorders.

Another interesting aspect of mtDNA is that, unlike chromosomal DNA, it is inherited from the mother only. This is true in most animals, plants, and fungi. As a result of this lopsided inheritance, mtDNA changes very little from mother to offspring and can be used to track ancestry back for hundreds of generations.

There are other historical mysteries that could be solved through mouse genetics. For example, Viking settlements across the North Atlantic - including Iceland, the Hebrides, and Canada - could  be verified by looking at mitochondrial DNA variability in mouse populations.

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