A grey squirrel on Oct. 18, 2021.
Credit: Avi SinghMost Penn students know that black squirrels are a common sight on campus now, but the unofficial fixtures of campus culture were likely introduced to Penn over 200 years ago.
“Black squirrels” — a term which can refer to any squirrel with fur that ranges from dark gray to jet black — result from specific genetic mutations. According to Sarah Tomke, a postdoctoral researcher at the Wildlife Futures Program at the School of Veterinary Medicine, squirrels were introduced to Philadelphia around the mid-1800s, making it likely that black squirrels were also brought to Penn’s campus around a similar time.
“Black squirrels are just a different color morph of the common gray squirrel,” Tomke said. “That’s caused by a genetic mutation in a very specific gene that controls how much melanin each cell expresses.”
This mutation, Tomke added, can also manifest itself as a version of genetic inheritance known as incomplete dominance, a condition in which a squirrel possesses both a version of the genetic mutation and the normal variant, resulting in brown fur rather than gray or black.
Tomke is currently involved in a phylogenetics research project on fox squirrels to determine the extent to which certain subspecies are related to one another. It is these fox squirrels, Tomke suggested, that may have been the origin of this genetic mutation found in black squirrels.
“A mutation like that is actually really rare to happen spontaneously,” she said. “Previous research found that this mutation probably came from fox squirrels a long time ago when gray squirrels and fox squirrels would hybridize with each other, and that mutation actually passed from fox squirrels into gray squirrels.”
Today, black squirrels have become a staple of Penn’s campus culture. Jessica Peterson, manager of the Common Press at the Fisher Fine Arts Library, highlighted how the black squirrel came to achieve mascot status not just at the Common Press but throughout campus.
“Everyone who works at Fisher is aware that in our tours and orientations when we start as employees, people point out there’s like a group of black squirrels that occupy the area by the ADA entrance and the Shakespeare Garden that’s in front of Fisher,” Peterson said. “So I just started adopting it, including it in our newsletters, and we have little buttons.”
Peterson added that events at the Common Press — such as their recent open studio “Black Squirrel Pattern Postcard Printing” event — are a testament to how students and staff around campus have become engaged with the campus squirrels on a regular basis.
“Like in that event, some people from Wharton came, and they give [stuffed] squirrels away as prizes in their behavioral labs,” she said. “So they brought us a [stuffed] squirrel. And then someone from the law school came and was like, ‘I have a whole blog about the black squirrels in front of the law school.’”
“It feels like a real community-building thing that’s kind of below the radar of the official dialog of the University,” she concluded. “It’s a unifying thing.”
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