University of Haifa
Got a mouse in the house? Blame yourself. Not your housekeeping, but your species. People never intended to live a mouse-friendly lifestyle. But as we adopted a settled life, some animals settled in, too, a new study shows. The success of some ancient mice followed the ups and downs of the earliest human settlements, new data show. When these communities of people thrived, certain mice did, too.
For their new study, scientists compared ancient mouse teeth with those of modern rodents that hang out near people who are only semi-settled. When humans make permanent homes, one mouse species moves in. When those people move on, another mouse species takes over.
These findings show that human settlements started long before people began to grow crops. And that suggests that the vermin were thriving off of our homes, not off of our stored food, the scientists conclude.
Between 15,000 and 11,000 years ago (a time called the Natufian period), people began to form small stone settlements in what is now Israel and Jordan. These communities were not yet farming or storing grain. People lived in a single place for a season or two. After moving on, they’d later come back to that place fairly often. By creating such a home base, those early settlers changed the ecosystem. Local plants and animals took advantage of new chances to grow and thrive.
Lior Weissbrod is an archaeologist in Israel at the University of Haifa. He looks for clues to the history of relationships between animals and people. He has always been interested in animal remains. But mouse teeth weren’t his first choice, he admits. “[At] the site I was going to work on, the remains of larger animals were already studied,” he says. “I was left with the small mammals.”
Small mammals have really tiny teeth. The largest mouse molars are only about 1 millimeter (0.04 inch) long. To collect them, Weissbrod spent a lot of time sifting dirt through a sieve with a very fine mesh. He collected 372 mouse teeth from the dirt at five archaeological sites in what is now Israel and Jordan. Those remains are 11,000 to 200,000 years old.
He gave the teeth to his colleague Thomas Cucchi. He’s an archaeologist at the National Museum of Natural History in Paris, France. Cucchi developed a technique to classify the mouse teeth by species. He did this based on tiny differences in their shape.
The human settlements Weissbrod studied had contained only a few homes each. But this small change for people was important to the tiny rodents. Based on the mouse teeth, it was clear that before people came along, the mouse species Mus macedonicus (Maeh-seh-DON-ih-kus) scurried through the undergrowth. After people and their stone buildings arrived, another species dominated — Mus domesticus (Doh-MES-tih-kus). When people left these settlements for about 1,000 years some 12,000 years ago, the reverse occurred: M. domesticus left and M. macedonicus returned.
The two species probably competed with each other when humans were absent, Weissbrod now suspects. But when people were around, M. domesticus took advantage of people being around. These mice may have had more flexible diets. They could live off our trash. And they feared people less.
“Once you get humans into the picture and human settlements … there’s a creation of a new habitat,” he explains. And one species — M. domesticus — took advantage of it to out-compete others, he says.
Weissbrod and his colleagues published their findings March 27 in the Proceedings of the National Academy of Sciences.
Ancient vs. modern vermin
Ancient samples alone were not enough to make a strong connection between human settlements and which species won the rights to be called a house mouse. The scientists also needed to look at a modern living situation that resembled the lifestyle that was typical of ancient peoples. For this, Weissbrod’s group turned to the Maasai (Mah-SYE). These are a nomadic group of cattle herders in southern Kenya.
“Maasai are nothing like ancient hunter-gatherers,” he notes. “But we look at specific things that make them comparable.” Maasai herders tend to live in small groups. And these East Africans use those settlements over and over. “The Maasai aren’t sedentary. They are on the verge perhaps,” he explains. “So they move [often] but not to the extent of highly mobile nomadic groups. They move on a seasonal basis.”
Two mouse species belonging to the Acomys genus live around Maasai settlements. Acomys mice are often called spiny mice, though scientists think they are more closely related to gerbils. One species is more likely to live near to people, the other to prefer sites without humans. The mice are easy to distinguish. A. wilsoni (Wil-SO-nee) has a short tail. A. ignites (Ig-NY-tees) has a longer tail.
Archaeologists usually work with dry and dusty fossils. Live, wiggling spiny mice were a new challenge for Weissbrod. But he got over his disgust. He went to Kenya and scooped up 192 of these critters from both species.
Like their ancient kin, one modern mouse had a competitive advantage when people were present. A. ignites made up 87 percent of the mice caught hanging out with the Maasai. In the non-settled area, fewer than half belonged to this species.
Weissbrod, Cucchi and their colleagues combined all this information about ancient and modern mice and people. Their findings now show how house mice came to live alongside us — no grain or farming required.
“We can show with a high degree of certainty now that mice became attached to us 3,000 years before farming,” Weissbrod reports. “From that we learned hunter-gatherers were making the transition to sedentary lives before farming. They didn’t need the crops to make that transition.”
Melinda Zeder is an archaeologist at the Smithsonian Institution in Washington, D.C. She wasn’t involved in the study. Zeder finds the new study “wonderful.” It’s impressive that such a big finding could come from such small samples, she says. “Out of the mouths of mice, we’re getting a wonderful view of a pivotal time in history.”
Other species also have taken the opportunity to hang out with people, Zeder notes. Wolves and wild boar arrived and “auditioned themselves for a starring role as a domesticate.” A few of the friendlier ones began to interact more with people. Those people began to see the advantages of the animals. By choosing to breed certain animals with each other, humans were able to select traits they prized. From wolves came dogs, and from wild boar came today’s pigs.
But when humans weren’t paying attention, other species moved in and thrived without the help of human breeders. Mice aren’t the only vermin that have arrived to “domesticate themselves,” Weissbrod says. Sparrows, pigeons, rats and other species have taken advantage of our presence. People may not find them useful. But that won’t stop them from using us.
cattle Also known as bovines (because they’re members of the subfamily known as Bovinae), these are breeds of livestock raised as a source of milk and meat. Although the adult females are known as cows and the males as bulls, many people refer to them all, generally, as cows.
colleague Someone who works with another; a co-worker or team member.
diet The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health.
domesticate (n.) A wild plant or animal species that has been bred into a tame version, usually over many generations. (v.) The process of cross-breeding various animals to get prized traits. Such a domesticated animal is one that has been bred in captivity for food or as a pet. A domesticated plant is one usually farmed or used for landscaping. (n. domestication)
ecosystem A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.
fossil Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.
habitat The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.
hunter-gatherer A human cultural group that feeds itself through hunting, fishing and gathering wild produce (such as nuts, seeds, fruits, leaves, roots and other edible plant parts). They can be somewhat nomadic and do not rely on agriculture for their foods.
kin Family or relatives (sometimes even distant ones).
mammal A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.
nomad (adj. nomadic) The name for someone who has not settled into any community or fixed site, but instead lives by moving from place to place over the course of a year in search of food and shelter.
Proceedings of the National Academy of Sciences A prestigious journal publishing original scientific research, begun in 1914. The journal's content spans the biological, physical, and social sciences. Each of the more than 3,000 papers it publishes each year, now, are not only peer reviewed but also approved by a member of the U.S. National Academy of Sciences.
rodent A mammal of the order Rodentia, a group that includes mice, rats, squirrels, guinea pigs, hamsters and porcupines.
sedentary Not physically active; an adjective for activities done largely while sitting.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
transition The boundary where one thing (paragraphs, ecosystems, life stage, state of matter) changes into another. Some transitions are sharp or abrupt. Others slowly or gradually morph from one condition or environment to another.
vermin Pest animals that people find noxious or disgusting — such as flies, lice, bedbugs, roaches, mice and rats. Owing to their size, speed and ability to reproduce quickly, these animals can be hard to control. Many also can spread disease.
Journal: L. Weissbrod et al. Origins of house mice in ecological niches created by settled hunter-gatherers in the Levant 15,000 y ago. Proceedings of the National Academy of Sciences. Vol. 114, April 18, 2017, p. 4099. doi: 10.1073/pnas.1619137114.