Raccoons Are Showing Early Signs of Domestication

Raccoons showing early signs of becoming domesticated

By Marina Wang Edited by Andrea Thompson

With dexterous child-like hands and cheeky “masks,” raccoons are North America’s ubiquitous backyard outlaws. In fact, these creatures are so comfortable in the human environment that a new study shows that raccoons living in urban areas are changing physically in response to living around humans – an early stage of domestication.

Studies show that the process of domestication is often mistakenly thought to have been initiated by humans – in which people capture wild animals and selectively breed them. But the study authors claim this process begins much earlier, when animals become acclimated to the human environment.

“One thing about us humans is that, wherever we go, we create a lot of waste,” says study co-author and University of Arkansas at Little Rock biologist Rafaela Lesch. Piles of human remains provide a bottomless reservoir for wildlife, and to access that bounty, animals must be brave enough to sift through human waste, but not so brave as to become a threat to people. “If you have an animal that lives in close proximity to humans, you have to be pretty well-behaved,” says Lesch. “That selection pressure is quite intense.”

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For example, proto-dogs may have dug up piles of human garbage, and cats were attracted to rats that gathered around garbage. Over time, individual animals whose fight-or-flight response was reduced could forage more successfully around humans and pass on their non-reactive behavior to their offspring.

Strangely, vulvalization has also long been associated with traits such as a small face, small head, floppy ears and white spots on the fur – a pattern noted by Charles Darwin in the 1800s. The occurrence of these characteristics is known as domestication syndrome, but scientists did not have a comprehensive theory until 2014 to explain how these characteristics were linked. That’s when a team of evolutionary biologists noticed that many of the physical traits that co-occur with domestication trace back to a key group of cells during embryonic development, called neural crest cells. In early development, these are formed along the back of the organism and move to different parts of the body, where they become important for the development of different types of cells. Biologists have hypothesized that mutations that hinder the proliferation and development of neural crest cells could subsequently lead to their shortened snouts, lack of cartilage in the ears, loss of pigmentation in the coat and reduced fear response – leading to better chances of survival in close proximity to humans.

Lesch says neural crest cells are the most prominent hypothesis that scientists have yet to explain domestication syndrome, but they are still gathering and evaluating evidence for or against it. One piece of the puzzle will be to see if domestication syndrome can be observed in real time with wild animals. For the new study, he and 16 undergraduate and graduate students collected nearly 20,000 photos of raccoons across the U.S. from the community science platform iNaturalist. The team found that raccoons living in urban environments had 3.5 percent shorter snouts than their rural relatives.

The findings fit with observations of urban foxes and rats and “indicate that once wild animals start spending time close to people, they become a little less fearful and perhaps even start showing physical signs of domestication syndrome,” says Adam Wilkins, a biologist at Humboldt University of Berlin, who first presented the neural crest cell explanation but was not involved in the new study.

Lesch would like to investigate further, perhaps trapping raccoons and comparing genetics or stress hormones between urban and rural animals. He and his colleagues can also test whether the patterns hold true for other species such as armadillos and opossums. “I would love to take the next steps to see if our trash pandas in our backyards are actually friendlier than pandas living in rural areas,” she says.

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