London: Global warming could make humans shorter; warn scientists who claim to have found evidence that it caused the world's first horses to shrunk nearly 50 million years ago.
In fact, a team from the universities of Florida and Nebraska says it has found a link between the Earth heating up and the size of mammals -- horses, in this case, the last time the world heated up.
The scientists used fossils to follow the evolution of horses from their earliest appearance 56 million years ago.
As temperatures went up their size went down, and vice versa; at one point they were as small as a house cat, said Dr Jonathan Bloch, curator of the Florida Museum of Natural History, was quoted by the 'Daily Mail' as saying.
The scientists say that the current warming could have the same effect on mammals -- and could even make humans smaller.
"Horses started out small, about the size of a small dog like a miniature schnauzer. What's surprising is that after they first appeared, they then became even smaller and then dramatically increased in size, and that exactly corresponds to the global warming event, followed by cooling.
"It had been known that mammals were small during that time and that it was warm, but we hadn't understood that temperature specifically was driving the evolution of body size," Dr Bloch said in the 'Science' journal.
The earliest known horse is known as Sifruhippus and appeared during a period known as the Paleocene-Eocene Thermal Maximum. This was a time of warming lasting 175,000 years, in which increased carbon monoxide saw temperatures gradually rise by between 10 and 20 degrees.
Studying fossils collected in Wyoming's Bighorn Basin, the researchers traced the evolution of Sifrhippus from a 12-pound animal that shrank during a 130,000-year period to 8.5 pounds -- the size of a small house cat -- then increased to about 15 pounds during the next 45,000 years.
Dr Ross Secord, from Nebraska university, said: "This is the highest-resolution terrestrial record of its kind from anywhere in the world and it shows how climate changed in Wyoming at that time."
The findings raise questions about how animals may respond to climate change in the future, he said.
He added: "We're seeing about a third of the mammals getting smaller and some of them getting a lot smaller, by as much as half of their original body size."