If you ever get a house, “eventually you get a mouse”—or so Ogden Nash once wrote. And science seems to be catching up with poetry. The standard thinking until now has been that the house mouse, Mus musculus, only began its intimate relationship with humans at the dawn of agriculture, roughly 11,500 years ago. In effect, you had to have a farm, not just a house, before mice moved in to raid the stored grain.
It turns out, however, that the house alone—a hut even—was enough to do the trick, according to a new study published Monday in Proceedings of the National Academy of Sciences. M. musculus began to hang around with humans, the study’s authors wrote, at least 15,000 years ago, during the so-called Natufian era in the Middle East, when late-stage hunter–gatherers were just beginning to adopt a more settled way of life. It was an on-again, off-again relationship at first, with both species occupying the same settlements for a season or a two at a time. But for the mouse—already becoming the house mouse—that early connection became the springboard to world conquest as one of humanity’s closest companions.
Even though the new study is limited to mice, co-author Fiona Marshall of Washington University in Saint Louis speculates house cats might also have begun their relationship with humans in the preagricultural period. (Cats tend to follow mice, as Ogden Nash noted, “in a trice.”) The study also relies on evidence from an archaeological dig at Ain Mallaha in northern Israel that is already well known for the earliest archaeological evidence of dog domestication: In a 15,000-year-old grave there, a woman buried in a loose fetal position rests her hand against the body of a small puppy.
The authors describe the preagricultural shift to a more settled way of life as “a turning point in human and environmental history” with “a profound, long-lasting and unpredictable influence on the human niche”—and the mice, cats, dogs and other familiar species that came to cohabit it.
To examine the mouse connection in detail, the researchers took a new look at seemingly insignificant specimens—mouse teeth that had been sitting on the shelf in a natural history museum for decades. The pioneering Israeli archaeozoologist Eitan Tchernov excavated many of them beginning in the 1950s, and he saw enough evidence even then to theorize about the unexpected abundance of house mice in hunter–gatherer settlements. “But he didn’t have the radiocarbon dates we have now,” says co-author Lior Weissbrod, an archaeozoologist at the University of Haifa. “The understanding of the timing of the Natufian really changed with carbon 14 dating and the switch to accelerator mass spectrometry” as a technique for accurately dating small samples, beginning in the 1980s.
The new study also had the advantage of high-precision digital photography and computer-assisted analysis to make side-by-side comparisons of 372 mouse teeth, from a 200,000-year span at five sites around Israel. That enabled the co-authors to distinguish easily, by the shape of the teeth, between the familiar, long-tailed M. musculus and its short-tailed cousin Mus macedonius. During periods of human occupation, the researchers found, musculus moved into human settlements, probably attracted by food waste and small stores of foraged barley, wild wheat and nuts.
Something about musculus made it better suited than M. macedonius to thrive in the dark corners of human habitations. A longer tail, for instance, might have made it more agile for climbing and for escape. In any case, the abundance of musculus specimens during periods of human occupation, the co-authors wrote, indicates musculus effectively outcompeted macedonius. But during periods when humans resumed their nomadic ways, macedonius took over again around their abandoned settlements.
The results are of interest, Weissbrod says, partly because “human intentionality,” which complicates the question of how cats or dogs became domesticated, does not really come into play with mice. “When we’re looking at mice and at shifting proportions of two mouse species over time, we are looking purely at ecology, the effects of settlements on mice, and not at human intentions.”
As a reality check on ancient ecology, the study also includes evidence about changing populations of two closely related mouse species in modern Kenya. On the southern border there, a Maasai community is now making the shift from a herding way of life to periods of increasing settlement, much as the Natufians did 15,000 years ago. And again, a long-tailed mouse, this time Acomys ignitus, appears to thrive in human habitations, outcompeting its short-tailed neighbor, Acomys wilsoni. The Maasai do not store large quantities of grain, says Weissbrod, who conducted that part of the study, and they expressed no strong feelings about the mice that had begun to live among them. Intentionality only turned up, he notes, among neighbors who farm and store grain, and tend to talk about mice, predictably, in terms of how to get rid of them.
The connection between mice and preagricultural humans “is certainly for me a new finding and interesting,” says Jeremy Searle, a Cornell University evolutionary biologist who has written extensively about domestication of both cats and mice but did not participate in the new study. “We have tended to think that house mice have been associated with humans only when there are large quantities of stored grain from farming.” He calls the study “genuinely a new approach.”
“I really love the fact that something like the house mouse—not a big keystone species, not high profile, not charismatic—is giving us a wonderful window on some of the more momentous events in human history,” adds the Smithsonian National Museum of Natural History’s Melinda Zeder, who also was not part of the work. “What this is showing,” says Zeder, an influential thinker on commensalism and domestication, is that the increasingly settled character of human communities “really has definite impacts on the natural world”—and not just in a negative way. “It’s building what one might call an anthropogenic niche, and it’s creating a host of opportunities.” For mice, of course, but also for archaeologists who “see this whole range of mesocarnivores affiliating with these human environments. The number of wild cat and fox bones increases dramatically as well as things like weasels, badgers, martens, polecats,” Zeder says. Until recently people tended to think about domestication as a matter of human mastery over nature, she adds. “But as we understand the process of domestication more, we see it in terms of these mutualisms, these ecological systems that people are part of,” with humans and other species each looking to its own advantage, sometimes to the benefit of both.
The new study fits this more mutual way of thinking about domestication, with preagricultural settlements like Ain Mallaha as the stage on which species—mice, cats, dogs and also humans in effect “tried out” for life with one another. We are still ambivalent about some of the resulting associations. Ogden Nash, for instance, thought cats were ultimately more annoying than mice. But for many of us, it was the beginning of some of our most beautiful friendships.