It’s become an all-too familiar image from the coronavirus scare of 2020—aisles of empty store shelves bereft of products like hand sanitizer, cans of soup and face masks. Oh yes, and toilet paper.

It’s that last item that has struck many as most puzzling. The symptoms of Covid-19, a respiratory illness, don’t suggest a need for vast quantities of toilet paper, while toilet paper manufacturers themselves say there have been no disruptions to their supply chains. So why has panicked buying and hoarding been so widespread, not just in Canada but in every country impacted by the virus?

Put simply, our human brains.