A scientist at the University of Leicester says rats may evolve to be the size of sheep as they fill ecological niches vacated by bigger animals that go extinct.
"Animals will evolve, over time, into whatever designs will enable them to survive and to produce offspring," according to geologist Dr Jan Zalasiewicz. (HeraldScotland.com)
Not impressed? How about the size of cows? That could happen (DailyMail.co.uk). It's happened before:
"For instance, in the Cretaceous Period, when the dinosaurs lived, there were mammals, but these were very small, rat and mouse-sized, because dinosaurs occupied the larger ecological niches.
"Only once the dinosaurs were out of the way did these tiny mammals evolve into many different forms, including some very large and impressive ones: brontotheriums, horses, mastodons, mammoths, rhinoceri and more.
"Given enough time, rats could probably grow to be at least as large as the capybara, the world's largest rodent, that lives today, that can reach 80 kilos (176 pounds).
"If the ecospace was sufficiently empty, then they could get larger still."
Zalasiewicz points out that humans have helped spread rats all around the world.
"They are now on many, if not most, islands around the world - and once there, have proved extraordinarily hard to eradicate. They're often there for good, essentially. Once there, they have out-competed many native species and at times have driven them to extinction."
Fortunately, gigantism -- when a small creature steps into an ecological niche left by a larger species -- doesn't happen overnight. It took 50 million years for the blue whale to evolve from an animal the size of a wolf.
Rats, like other animals, won't just evolve size-wize, Zalasiewicz says.
"There will be future thin rats, future fat rats, slow and heavy rats, fast and ferocious rats, probably future aquatic rats - the list goes on. Other animals will likely follow the same pattern, such as domestic cats, rabbits, goats and more."