The Sixth Extinction: An Unnatural History by Elizabeth Kolbert:
That evening in Moffat, once everyone had had enough of tea and graptolites, we went out to the pub on the ground floor of the world’s narrowest hotel. After a pint or two, the conversation turned to another one of Zalasiewicz’s favorite subjects: giant rats. Rats have followed humans to just about every corner of the globe, and it is Zalasiewicz’s professional opinion that one day they will take over the earth.
“Some number will probably stay rat-sized and rat-shaped,” he told me. “But others may well shrink or expand. Particularly if there’s been epidemic extinction and ecospace opens up, rats may be best placed to take advantage of that. And we know that change in size can take place fairly quickly.” I recalled a rat I once watched drag a pizza crust along the tracks at an Upper West Side subway station. I imagined it waddling through a deserted tunnel blown up to the size of a Doberman.