Evolution: How the rhino got his woolly NOWADAYS, elephants and rhinoceroses are tropical species. Until recently, though, they wandered as far north as the Arctic Ocean. The last woolly rhino died about 8,000 years ago. Woolly mammoths lasted another 3,500 years, succumbing only when human beings arrived in their Siberian refuges. What no one has known, however, is when and where these animals evolved the eponymous coats that allowed them to range in such high latitudes. The best guess was that they grew them gradually, as ice began to grip the world 2.6m years ago. But in the case of the woolly rhino Xiaoming Wang, of the Natural History Museum of Los Angeles County, and Deng Tao, of the Institute of Vertebrate Palaeontology and Palaeoanthropology in Beijing, disagree. They think woolly rhinos arrived in the ice-age tundra fully formed, and suspect other beasts may have done so, too. In their view it was not global climate change that forced rhinos to sport shaggy coats, but rather a trip on a geological elevator. They believe the change happened when the beasts were uplifted by plate tectonics to become inhabitants of the world's penthouse suite: the plateau of Tibet. The two researchers" evidence, as they explained to a joint meeting of the Geological Societies of China and America, held recently in Chengdu, the capital of Sichuan province, is the partial skeleton (a skull, a jawbone and a couple of vertebrae) of a primitive species of woolly rhinoceros. This specimen, found in the Zanda Basin of south-western Tibet, dates from 3.7m years ago - well before the ice ages got going. It is smaller than an ice-age woolly rhino, but recognisably similar. In particular, though its horn has been lost, the place where it was attached to its skull is flanked by the sort of crest associated with the flat horns of the ice-age woolly rhino. These rhinos probably used their horns to scrape away snow that covered their food. At the moment the Zanda basin is 4,000 metres above sea level. But fossil snails found near the rhino suggest that when it was alive the area was as much as 5,500 metres up. It must therefore have subsided after having been thrown up during the collision of India with Asia, which created Tibet. Such altitude would have produced just the sort of selective pressure needed for woolly coats, flat horns and other adaptations to the cold to evolve. This done, the ice ages would have made the rest of the world a friendly place. Rhinos are an ancient lineage. The woolly rhino's closest living ancestor, as proved by looking at the genes of frozen specimens, is the Sumatran rhino. The line these two belong to split from those leading to the other four modern rhino species some 26m years ago, when Tibet was lower than it is now, so the hypothesis of Dr Wang and Dr Deng is plausible. And if it were true for rhinos, it might be true for other ice-age species. No ancestral mammoth has yet been found in Tibet, though elephants were abundant in both southern Asia and much of China until people arrived (they are rare in both now). But Dr Wang and Dr Deng have made one potentially pertinent discovery. When they compared the DNA of Tibetan yaks with that of American bison, they found the two species are closely related. Bison are the largest surviving representatives of the ice-age megafauna. Perhaps these icons of the old American West also started life half a world away in the fastnesses of Tibet.