Researchers have found that rats could evolve, over time, into super-sized rodents that are bigger than sheep and weigh as much as a person.
Geologist Dr Jan Zalasiewicz, from the University of Leicester, said that given enough time, rats could probably grow to be at least as large as the capybara, the world's largest rodent, which can reach at least 12.5 stone, the Daily Express reported.
Zalasiewicz asserted that if the ecospace was sufficiently empty, then they could get larger still.
Zalasiewicz explained that animals will evolve, over time, into whatever designs will enable them to survive and to produce offspring.
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, Zalasiewicz said.
Zalasiewicz said that only when the dinosaurs were out of the way did these tiny mammals evolve into many different forms, including some very large ones.
The largest rodent known to roam earth is the extinct Josephoartegasia monesi, which was larger than a bull and weighed over a tonne.
Dr Zalasiewicz also said that there are 'rat islands' all across the world, where rats are the dominant species, and once they are established they are "extraordinarily hard to eradicate".
