‘Self-domesticating’ mice suggest some animals tamed themselves without human intervention

By Roni Dengler

From the floppy ears of dogs to the curly tails of pigs, domesticated animals sport a different look than their wild cousins—a look that scientists chalked up to human intervention. Now, a new study of wild mice shows that they, too, can develop signs of domestication—white fur patches and short snouts—with hardly any human influence. The work suggests that the mice are able to tame themselves, and that other animals like dogs may have done the same before they were fully domesticated by humans.

Much of what we know about how animals change appearance during domestication comes from a famous experiment in Siberia in the 1950s. Researchers found that when they took wild foxes and let only the tamest breed, the foxes began to develop doglike features such as curly tails, smaller heads, and floppy ears. Nearly 100 years earlier, Charles Darwin dubbed this suite of traits “domestication syndrome.” But could these traits arise without any human intervention? An experimental accident suggests they can.

The accident began in 2002 when scientists studying mouse behavior and disease transmission trapped a dozen wild mice in a barn in Illnau, Switzerland. The animals were free to come and go and nest and mate as they pleased. Their new digs were also safe from predators—the mouse doorways were too small to allow domestic cats, owls, and martens to enter. The barn also contained plenty of free food and water, provided by the researchers every few weeks. The mice that didn’t mind the visits stuck around and eventually blossomed to a steady population of 250–430 animals. Some even began to run over the researchers’ shoes instead of scurrying away. That’s a sign that these animals had lost their fear of humans, even without the researchers deliberately breeding the most human-friendly mice, as scientists had done with the foxes.

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