Urban fox
New research suggests the bone structure of foxes living in cities can change systematically over the course of a few decades. According scientists from the University of Glasgow, this may be evidence of genetic evolution on a timescale observable by humans.
Kevin Parsons, who led the project, said his first inspiration for the study came from observing foxes near his bus station when he moved to the United Kingdom. The foxes would walk right by his feet and look up at him. He had never seen foxes so comfortable around people.
When the National Museum of Scotland got a donation of 1,500 fox skulls, Parsons got a chance to study how city life changes foxes. He said he knew there might be interesting results because of his background in urban ecology. Parsons said the study was a small commitment on his part because it didn’t require extra funding.
“I thought, why not take a look?” he said.
The skulls, which were from a cull in the early 70s, were labeled, so Parsons and his team knew exactly where each fox was killed. Foxes have only been in English cities since the 1930s.
Analysis of the skulls showed that foxes caught in London had shorter snouts and smaller brain cases than foxes from the countryside. There were also fewer differences between male and female foxes in the city.
The new study was published in Proceedings of the Royal Society B.
The changes observed in urban foxes are similar to changes Russian scientists discovered during a project to domesticate foxes, said Parsons. The scientists bred foxes with friendlier personalities and foxes with more aggressive personalities. Generations later, friendlier foxes had shorter snouts and smaller brain cases compared to the more aggressive ones.
Why these changes happen is not clear. Parsons said the fox personality traits and skull shape might be connected in development. If calmer foxes do better around humans and are more successful in cities, the different skull shapes could come along with that selection pressure.
He said the change to a shorter snout follows the long-term evolutionary trajectory of foxes compared to their ancient ancestors.
It is also possible that the skull shape has some advantages in the city. Parsons said a shorter snout allows for a more powerful bite while a longer snout gives foxes a faster bite. Biting faster might be more important when hunting in the country while biting hard might be good for fighting over food scraps in the city.
Arkhat Abzhanov, a natural sciences professor at Imperial College London, said that evolution of dramatic variation can occur quickly in mammals like domesticated dogs.
But he said it is possible that the change in skulls shape isn’t just genetic.
Skull and jawbones in developing mammals can change based on diet, Abzhanov said. For example, hyenas fed soft diets in zoos have more slender and pup-like skulls when compared to hyenas that grew up in the wild and cracked zebra bones for lunch. He said the study’s findings are interesting, but he is curious about the proportion of the difference that is due to genetics versus being raised in different environments.
