When did humans settle down? The house mouse may have the answer

Sometime about 10,000 years ago, the earliest farmers put down their roots—literally and figuratively. Agriculture opened the door to (theoretically) stable food supplies, and it let hunter-gatherers build permanent dwellings that eventually morphed into complex societies in many parts of the world. But how that transition played out is a contentiously debated topic. Now, a new study shows that our path to domesticity zig-zagged between periods of sedentary life and a roaming hunter-gatherer lifestyle. The evidence? The presence—and absence—of the common house mouse.

“It’s remarkable, using a lowly house mouse to monitor a major milestone in human history,” says Melinda Zeder, curator of Old World archaeology at the Smithsonian National Museum of Natural History in Washington, D.C., who wasn’t involved with the study. “It’s really a masterful way of monitoring sedentism.”

To explore the transition to agriculture, scientists have looked to the Natufians, an ancient hunter-gatherer society that flourished from about 12,500 to 9500 B.C.E. in a part of the Middle East called the Levant, which includes pieces of modern-day Cyprus, Syria, Israel, Jordan, Lebanon, and Palestine. The Natufians were among the first people known to domesticate animals—dogs and hogs—and may have been the first to transition to farming. As they moved from seasonally collecting acorns and hunting gazelle to farming wheat and barley, many researchers think they went through an intermediary phase: a semisedentary period in which they built stone dwellings but still hunted for sustenance and moved on when resources became scarce. But evidence of exactly when and how humans became sedentary has been hard to come by.

So Thomas Cucchi, an archaeologist at the University of Aberdeen in the United Kingdom, decided to turn to the creatures living alongside humans at the time, specifically house mice (Mus domesticus), which live almost exclusively in or near houses and planted fields. He teamed up with Lior Weissbrod, a fellow archaeologist at the University of Haifa in Israel, who was analyzing wild and domesticated mice living today in Kenya.

Cucchi, Weissbrod, and colleagues looked at hundreds of mouse molars from five different cave and open-air sites across the Levant. They found a zig-zagging pattern over time. Some 200,000 years ago, before the Natufians came on the scene, 100% of the molars belonged to wild Macedonian mice (Mus macedonicus). By the Early Natufian, 15,000 years ago, all the molars came from house mice. That likely meant the Natufians were becoming more sedentary, building semipermanent structures and discarding food waste that the domestic mice were better at exploiting. Curiously, about 13,000 years ago, the advantage swung back to the wild mice, coinciding with archaeological evidence that the Natufians were building smaller structures and using them less often. About 1000 years later, the house mouse came back to prominence, making up 80% of the molars. By the Early Neolithic, about 10,000 B.C.E.—the dawn of the agricultural age—this domestic species again accounted for all the mouse molars at the sites.

“These settlements were allowing the house mouse to completely exclude its competitors,” Weissbrod says. “The only way to create this effect would be for the Natufians to be staying in one place for quite some time.” The data suggest the Natufian hunter-gatherers alternated between nomadic and sedentary lifestyles for thousands of years before settling into agriculture, the researchers report today in the Proceedings of the National Academy of Sciences.

To be sure their pattern wasn’t a random archaeological accident, Weissbrod and Cucchi turned to two species of modern mice, the relatively domestic fiery spiny mouse (Acomys ignitus) and the comparatively wilder Wilson’s spiny mouse (A. wilsoni) that today live in the same region as the seminomadic Maasai people in Kenya and northern Tanzania. Traditionally most Maasai hunt, gather wild fruits and vegetables, and raise cattle, but do little farming, making their way of life a fair surrogate for that of the preagricultural Natufians, Weissbrod says, although it should be noted that the Maasai are a fully modern people no more closely related to early hunter-gatherers than are any other people on Earth. The researchers found that the longer the Maasai occupied an area, the more the tamer A. ignitus outcompeted the wilder A. wilsoni.

This pattern convinced the researchers that their conclusions about the Natufians were likely true. Weissbrod says archaeological evidence of competition between domesticated and wild species could be a powerful new tool to identify when other cultures around the world began settling down.

The new study is valuable, says anthropologist Lisa Maher of the University of California, Berkeley, who studies hunter-gatherer societies, but it also highlights how little we know about what drove ancient people toward a sedentary lifestyle. It also supports the idea that sedentism isn’t a necessary precursor to agriculture. “It does seem clear that sedentism and agriculture are separate things, each with their own timeline and trajectory of development,” she wrote to Science in an email.

Beyond what the study says about their living habits, it demonstrates just how much early humans influenced life around them, Zeder adds. “Humans are masters at creating niches. Our shaping of our environment is as old as our history.”