Most people are all too familiar with house mice. We know them as the eaters of crumbs, gnawers of cords, and leavers of droppings. They create the pitter-patters we hear in the night and the messes we find in the morning.
Conventional wisdom has said that mice and people began living together when humans learned to farm. But new research published today in the Proceedings of the National Academy of Sciences suggests that our relationship with these rodents may be even more ancient.
By studying the fluctuations of house mouse fossils found in archaeological sites in the eastern Mediterranean, scientists have revealed that Mus musculus domesticus first cozied up to humans around 15,000 years ago.
That would be about 3,000 years before the advent of agriculture.
The findings offer an unusual glimpse into a murky period of human development, since the abundance of house mice teeth seems to track with our nomadic ancestors’ early experiments in settling down.
That makes the new study “a nice example of how house mouse research can be helpful for studying our own history,” says Miloš Macholán, an evolutionary biologist and co-author of The Evolution of the House Mouse.
For example, scientists studying the transition from the hunter-gatherer lifestyle to agriculture may now be able to fill in gaps in the archaeological record by looking for the presence and proportions of mice molars, he says.
“I’d say it’s important to understand that mice have been accompanying us for a very long time,” says study leader Lior Weissbrod, a zooarchaeologist at the University of Haifa in Israel. “We’ve been changing them and they’ve been changing us in ways that are not immediately apparent.”
A Tale of Two Mice
The new study examines the rise of the house mouse in the Levant, an area that today encompasses parts of Israel, Lebanon, and Syria. Here, researchers previously found archeological sites left by the Natufian culture of hunter-gatherers roughly 15,000 years ago.
By examining fossil teeth found at these sites, the team discovered that the house mouse’s story is deeply intertwined with that of another closely related mouse species named Mus macedonicus. More commonly called the short-tailed mouse, this rodent is considered to be more wild and less tolerant of humans.
As the Natufian hunter-gatherers started to become more sedentary, likely as a result of favorable climate conditions, the team found a rise in the amount of house mouse molars in and around human settlements.
Weissbrod says the critters were probably attracted to the small caches of wild grains the humans had to store to survive without constantly moving from place to place. (Also read "New Clues on How and When Wolves Became Dogs.")
What was a boon for house mice, though, seems to have been a detriment to the meeker short-tailed mice. As house mouse molars start to pile up during periods of prolonged human habitation, short-tailed mice molars all but disappear.
However, when the climate shifted again and the region became cold and dry, the Natufians reverted to their original way of life, only staying in one place as long as the resources nearby could support them. During these spells, the researchers found that the more independent short-tailed mice become dominant once again.
A Modern Analog
The link between such human settlements and house mouse fluctuations became even clearer when the team compared their fossil results to mouse populations around today’s hunter-gatherers.
The Maasai of southern Kenya still practice a semi-mobile lifestyle, herding cattle to different areas depending on the season. Like the ancient Natufians, the modern Maasai live in proximity to two closely-related mouse species, Acomys wilsoni and Acomys ignitus.
Weissbrod and his colleagues set up rodent traps in and around Maasai settlements. While populations of the two rodents were nearly equal in these areas, the traps inside Maasai homes caught far more A. ignitus (87 percent) than A. wilsoni (13 percent).
This was astonishing, says Weissbrod, because they observed almost the exact same ratio between house mice (80 percent) and short-tailed mice (20 percent) from the Jordan Valley site of Ain Mallaha, a Natufian settlement that dates to between 12,000 and 13,000 years old—placing it in between the time periods of nomadic life and the earliest farmers.
“This then gave us the key that we needed to make sense of varying mouse proportions in all of our other samples from both earlier and later periods,” says Weissbrod.
The findings are “very cool and exciting,” says Keith Dobney, a bioarchaeologist at the University of Liverpool, because they provide a “new, detailed window on the past.”
Not only does the research show that the house mouse out-competed another mouse species by developing a one-sided relationship with humans, the authors have also tracked the fits and starts that eventually led to a sedentary lifestyle for hunter-gatherers in the Levant, simply by following the rodent’s rise and fall.
The relationship between humans and mice is still continuing to evolve, of course. Some people keep the docile domesticated mice as pets, and there’s an argument to be made that we owe the little squeakers our thanks for their enormous role in biomedical research.
Whether you feel ambivalence, ire, or gratitude, it seems our relationships with mice are as complex as they are ancient.