Rats the size of DOGS might roam Earth one day, scientist claims – and they could evolve to be ‘whales’ of the future

RATS could one day be the size of dogs - and the building blocks for the "whales of the future", a scientist has claimed.

Super-size rodents will be commonplace in a few million years.

The average size of a rat in the 21st Century is between 6cm to 9cm.

But people are already noticing that they are growing in size.

This is because the evolutionary process for rats has been sped up by their short lifespan and quick breeding process.

“After a mass extinction, in the recovery period after tens of millions of years, all kinds of new designs appear from whatever is left," Jan Zalasiewicz, a geologist and professor at the University of Leicester, told The Sun.

“When you think back to when the dinosaurs died out 66million years ago, then the mammals, which had been very small… essentially rat like creatures, they evolved within 33milllion years to give you the mammoths, the whales, all kinds of organisms essentially from rat-sized ancestors.”

The Blue Whale - a sea beast which can grow up to 30metres in length - has an ancestor that was the size of a dog, paddling at the edge of the sea about 50million years ago.

But you can trace its genealogy all the way back to a rat-like creature, according to Zalasiewicz.

The length of a medium-size dog is about 45cm.

Now Earth is facing another mass extinction, due in part to wildlife eradication, climate change and industrial livestock production.

Animals used for food - like cows, sheep and pigs - now account for more than half of mammals on the entire planet in terms of weight, a study published earlier this year by the Proceedings of the National Academy of Sciences revealed.

According to Our World in Data, the size of most other animal populations has collapsed by nearly 70% on average since 1970.

Populations of larger animals, such as rhinos, elephants, leopards and gorillas, have been hit harder than others.

But rats are "well placed" to become the ancestors of whatever comes next, Zalasiewicz explained.

Animals have to adapt to a changing world or die out, added Zalasiewicz.

With sea levels continuing to rise, “rats may develop into the seals and the whales of the future", he said.

“Some forms [of evolution] can take place quite quickly," he continued, adding that this could be why reports of 'super rats' are increasing.

Zalasiewicz said: "Rats are doing well because they can adapt themselves to living off the cast offs of people in towns or cities.

"Just as humans have gotten bigger and better fed since the Middle Ages."

Rats can swim too - albeit not across oceans.

But their comfortability with water is what puts them in a good position to survive in a rapidly changing environment and grow to new sizes.

"If we kill off most of the big impressive animals on Earth, we’ll be left with a world of tiny, small and medium-sized animals," said Zalasiewicz.

"So when the pressure is off, there'll be the opportunity [for rats] to grow larger again."

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