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.

科学家警告说，全球变暖可能会使人类变矮。科学家宣称已经找到证据：近5000万年前全球变暖就曾让世界上最早的马个头变小。

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 vice¹ versa; at one point they were as small as a house cat, said Dr Jonathan Bloch, curator（馆长，监护人） 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（雪纳瑞狗） . 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.