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Could global warming turn us all into hobbits?

A study of prehistoric horses has found that rising temperatures tend to make mammals shrink. Does that apply to humans too? 

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A new study has found that, as the planet heated rapidly some 56 million years ago, Sifrhippus, the earliest known horse, shrunk to about three-quarters of its size. If this tendency is true for humans, we could be approaching the stature of Frodo and Sam shown here in 'The Lord of the Rings: The Two Towers.'

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It's been long known that the Earth's rising surface temperatures portend mass extinction, prolonged droughts, extreme weather, and rising seas. Now we can add a new worry: Humanity could be transformed into a race of hobbits.

New research reveals the extent to which global temperatures can influence the evolution of the size of mammals. Hot weather tends to make them smaller, and cold weather tends to make them grow.

About 56 million years ago, our planet underwent a major temperature swing. Nobody knows what initially caused it – conjectures include volcanic activity, a comet impact, a sudden release of methane from the ocean, and natural variations in the Earth's orbit – but we know that, over a period of about 175,000 years, temperatures increased 9 to 18 degrees Fahrenheit, and then suddenly dropped. 

During this time, an equine creature roamed the forests in what is now Wyoming's Bighorn BasinSifrhippus sandrae, the earliest known horse, doesn't look much like today's horses. For one thing, it weighed only 12 pounds or so and was roughly the size of a small dog. 

And it was destined to get even smaller. A study of Sifrhippus molars unearthed in Wyoming and kept at the Florida Museum of Natural History at the University of Florida in Gainesville found that the animals shrunk to about eight pounds over the first 130,000 years of warming, and then shot back up to 15 pounds during the next 45,000 years as the planet cooled again.

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