Four-legged stowaways hitched a ride aboard the wooden 10th- and 11th-century Viking ships that braved the northern seas. The probably numerous passengers aboard hailed from Mus musculus domesticus, the small, fleet-of-foot rodent otherwise known simply as the house mouse.
Opportunistic hangers-on have accompanied human migrations throughout history. From the louse to the mouse, scientists have started using detailed DNA evidence from these species to see how these animals have spread along with our own settlements. A new study, published online March 18 in BMC Evolutionary Biology, shows that Norwegian Vikings brought mice along in their conquests, some of whose descendants persist to this day in the far-flung destinations visited.
"We can match the pattern of human populations to that of the house mice," Eleanor Jones, of the University of York and Uppsala University and a co-author of the study, said in a prepared statement. "Human settlement history of the last 1,000 years is reflected in the genetic sequence of mouse mitochondiral DNA."
She and her colleagues collected genetic evidence from mouse bones uncovered in archeological digs at Viking settlements in Iceland and Greenland, settlements that date back to the 10th century. The researchers then compared the ancient DNA with samples of modern mouse DNA collected from the same regions.
Perhaps 11th-centry Vikings don't sound like the most domestic of settlers, but they took with them the trappings of home, which included semi-stable dwellings that at least made a house good enough for a mouse.
The mice also might have tagged along with the Vikings during their relatively short foray to Newfoundland around the year 1000. But if they did, then "like the Vikings, their presence was fleeting," noted Jeremy Searle, another co-author and a professor at Cornell University, in a prepared statement. And that is not terribly surprising. Local indigenous tribes lived in the area at the time, but their more spare, nomadic life style might have been inadequate for the more domestic mouse. Modern-day Newfoundland is by no means mouse-less, of course. The current house mouse found there descended primarily from a British mouse lineage that arrived in the 15th century.
Closer to the Viking's homeland, Iceland's house mouse, like its human population, exhibits scant genetic diversity, suggesting the presence of small initial founding events: the rodents who came with the Vikings rarely had their genetic pool supplemented by later arrivals to the island.
Greenland also boasts a mouse populace whose fortunes rose and fell with their human shipmates. The house mouse seems to have arrived, languished and then was reestablished from a different homeland, likely Denmark.
As genetic sequencing technology improves to let us peer back farther into the past, scientists will continue to follow the DNA crumbs, which, in the case of house mice, will likely lead us to our own hearths.