The National Museums Scotland has a collection of about 1,500 fox skulls, diligently labeled with their original locations in London and the surrounding countryside. And when researchers compared rural fox skulls to those from in the city itself, they found some key differences.
The results, published on June 3 in the Proceedings of the Royal Society B, show that while rural foxes remain adapted for speed and hunting small, scampering prey, urban foxes have different priorities. Their skulls reflect the different needs of a carnivore that scavenges in a city chock-full of human refuse, ripe for the taking by a cunning canine. Shorter, stronger snouts are better adapted for breaking open packaging and crunching leftover bones, and smaller brains are fine when their meals don’t run away, Virginia Morell reports for Science magazine.
Together, the characteristics resemble what Charles Darwin labeled “domestication syndrome,” a set of traits that accompany a wild animal’s transition to tameness and eventually domestication.
“What’s really fascinating here is that the foxes are doing this to themselves,” Kevin Parsons, an evolutionary biologist at the University of Glasgow, tells the BBC in a video. “This is the result of foxes that have decided to live near people, showing these traits that make them look more like domesticated animals.”
But, the researchers stress, the urban foxes are definitely not house pets. Instead, the differences illuminate the path that dogs and cats may have taken early in their paths toward human companionship.
The fox skulls were collected between 1971 and 1973, when the animals were being culled and London boroughs were responsible for handling their fox populations. According to London’s Natural History Museum, attempts to cull the urban foxes were unsuccessful because the populations are self-regulating, and when one animal was killed then another would take its territory within days. The city abandoned fox culls in the 1980s, although fox control measures were raised for discussion again in recent years.
The skulls served as a snapshot of a large fox population in the early 1970s. Parsons photographed 111 skulls—57 female and 54 male—from rural and urban areas and identified key features in the skulls’ shapes. He and his team found that a fox’s habitat has a noticeable effect on the shape of the skull. A rural fox’s long, tapered snout is ideal for agility, but an urban fox doesn’t need speed since its energy is better spent digging through a trash pile than hunting prey.
“They also have a smaller brain case, so they may have smaller brains in the urban environment,” Parsons tells the BBC. “So an evasive prey that’s scooting back and forth and trying to avoid capture is going to be much more mentally challenging for a fox than the stationary prey, the stationary food that an urban fox will come across.”
The changes in the urban fox skulls also line up with a long-running study into fox domestication in Russia. The study began in the 1960s, and after generations of breeding only the least aggressive, most human-friendly foxes, the animals have traits like curled tails, floppy ears, short snouts and barking. (A recent paper raised questions about whether the traits are actually associated with domestication, or if they’re a result of the original gene pool of 130 foxes in the study.)
But in regards to the new study, “I’m not so much surprised as delighted,” by the results, evolutionary biologist Lee Dugatkin of the University of Louisville, who wasn’t involved in the study, tells Science magazine. “This is a ‘natural experiment’ that is very much in line with what the Russian experiment has found.”
The foxes are nowhere near as domesticated as familiar animals like dogs or cats, but the study shows in a heavily human environment like a city is enough to nudge animals down a domesticated evolutionary path.
“[Foxes] never move any farther down the path to domestication,” than what is observed in the study, Melinda Zeder, emeritus archaeologist at the Smithsonian National Museum of Natural History, tells Science. “We don’t know why.”